1
|
Daigle A, Johri P. Hill-Robertson interference may bias the inference of fitness effects of new mutations in highly selfing species. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.06.579142. [PMID: 38370745 PMCID: PMC10871249 DOI: 10.1101/2024.02.06.579142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
The accurate estimation of the distribution of fitness effects (DFE) of new mutations is critical for population genetic inference but remains a challenging task. While various methods have been developed for DFE inference using the site frequency spectrum of putatively neutral and selected sites, their applicability in species with diverse life history traits and complex demographic scenarios is not well understood. Selfing is common among eukaryotic species and can lead to decreased effective recombination rates, increasing the effects of selection at linked sites, including interference between selected alleles. We employ forward simulations to investigate the limitations of current DFE estimation approaches in the presence of selfing and other model violations, such as linkage, departures from semidominance, population structure, and uneven sampling. We find that distortions of the site frequency spectrum due to Hill-Robertson interference in highly selfing populations lead to mis-inference of the deleterious DFE of new mutations. Specifically, while accounting for the decrease in the effective population size due to linked effects of selection allows an accurate estimation of selection coefficients in moderately selfing populations, this correction is unable to accurately estimate selection coefficients in highly selfing populations when interference between selected alleles is pervasive. In addition, the presence of cryptic population structure with low rates of migration and uneven sampling across subpopulations leads to the false inference of a deleterious DFE skewed towards effectively neutral/mildly deleterious mutations. Finally, the proportion of adaptive substitutions estimated at high rates of selfing is substantially overestimated. Our observations apply broadly to species and genomic regions with little/no recombination and where interference might be pervasive.
Collapse
|
2
|
Kyriazis CC, Serieys LE, Bishop JM, Drouilly M, Viljoen S, Wayne RK, Lohmueller KE. The influence of gene flow on population viability in an isolated urban caracal population. Mol Ecol 2024; 33:e17346. [PMID: 38581173 PMCID: PMC11035096 DOI: 10.1111/mec.17346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 01/23/2024] [Accepted: 03/26/2024] [Indexed: 04/08/2024]
Abstract
Wildlife populations are becoming increasingly fragmented by anthropogenic development. Small and isolated populations often face an elevated risk of extinction, in part due to inbreeding depression. Here, we examine the genomic consequences of urbanization in a caracal (Caracal caracal) population that has become isolated in the Cape Peninsula region of the City of Cape Town, South Africa, and is thought to number ~50 individuals. We document low levels of migration into the population over the past ~75 years, with an estimated rate of 1.3 effective migrants per generation. As a consequence of this isolation and small population size, levels of inbreeding are elevated in the contemporary Cape Peninsula population (mean FROH = 0.20). Inbreeding primarily manifests as long runs of homozygosity >10 Mb, consistent with the effects of isolation due to the rapid recent growth of Cape Town. To explore how reduced migration and elevated inbreeding may impact future population dynamics, we parameterized an eco-evolutionary simulation model. We find that if migration rates do not change in the future, the population is expected to decline, though with a low projected risk of extinction. However, if migration rates decline or anthropogenic mortality rates increase, the potential risk of extinction is greatly elevated. To avert a population decline, we suggest that translocating migrants into the Cape Peninsula to initiate a genetic rescue may be warranted in the near future. Our analysis highlights the utility of genomic datasets coupled with computational simulation models for investigating the influence of gene flow on population viability.
Collapse
Affiliation(s)
- Christopher C. Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA
| | - Laurel E.K. Serieys
- Panthera, 8 W 40th St, 18th Floor, New York, NY 10018, USA
- Institute for Communities and Wildlife in Africa, Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, South Africa
| | - Jacqueline M. Bishop
- Institute for Communities and Wildlife in Africa, Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, South Africa
| | - Marine Drouilly
- Panthera, 8 W 40th St, 18th Floor, New York, NY 10018, USA
- Institute for Communities and Wildlife in Africa, Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, South Africa
- Centre for Social Science Research, University of Cape Town, Rondebosch, 7701, South Africa
| | - Storme Viljoen
- Institute for Communities and Wildlife in Africa, Department of Biological Sciences, University of Cape Town, Rondebosch, 7701, South Africa
| | - Robert K. Wayne
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA
| | - Kirk E. Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, CA 90095, USA
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
| |
Collapse
|
3
|
Dabi A, Schrider DR. Population size rescaling significantly biases outcomes of forward-in-time population genetic simulations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.04.07.588318. [PMID: 38645049 PMCID: PMC11030438 DOI: 10.1101/2024.04.07.588318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/23/2024]
Abstract
Simulations are an essential tool in all areas of population genetic research, used in tasks such as the validation of theoretical analysis and the study of complex evolutionary models. Forward-in-time simulations are especially flexible, allowing for various types of natural selection, complex genetic architectures, and non-Wright-Fisher dynamics. However, their intense computational requirements can be prohibitive to simulating large populations and genomes. A popular method to alleviate this burden is to scale down the population size by some scaling factor while scaling up the mutation rate, selection coefficients, and recombination rate by the same factor. However, this rescaling approach may in some cases bias simulation results. To investigate the manner and degree to which rescaling impacts simulation outcomes, we carried out simulations with different demographic histories and distributions of fitness effects using several values of the rescaling factor, Q , and compared the deviation of key outcomes (fixation times, fixation probabilities, allele frequencies, and linkage disequilibrium) between the scaled and unscaled simulations. Our results indicate that scaling introduces substantial biases to each of these measured outcomes, even at small values of Q . Moreover, the nature of these effects depends on the evolutionary model and scaling factor being examined. While increasing the scaling factor tends to increase the observed biases, this relationship is not always straightforward, thus it may be difficult to know the impact of scaling on simulation outcomes a priori. However, it appears that for most models, only a small number of replicates was needed to accurately quantify the bias produced by rescaling for a given Q . In summary, while rescaling forward-in-time simulations may be necessary in many cases, researchers should be aware of the rescaling effect's impact on simulation outcomes and consider investigating its magnitude in smaller scale simulations of the desired model(s) before selecting an appropriate value of Q .
Collapse
Affiliation(s)
- Amjad Dabi
- Department of Genetics, University of North Carolina, Chapel Hill, North Carolina, USA
| | - Daniel R. Schrider
- Department of Genetics, University of North Carolina, Chapel Hill, North Carolina, USA
| |
Collapse
|
4
|
Rodrigues MF, Kern AD, Ralph PL. Shared evolutionary processes shape landscapes of genomic variation in the great apes. Genetics 2024; 226:iyae006. [PMID: 38242701 PMCID: PMC10990428 DOI: 10.1093/genetics/iyae006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 10/26/2023] [Accepted: 01/03/2024] [Indexed: 01/21/2024] Open
Abstract
For at least the past 5 decades, population genetics, as a field, has worked to describe the precise balance of forces that shape patterns of variation in genomes. The problem is challenging because modeling the interactions between evolutionary processes is difficult, and different processes can impact genetic variation in similar ways. In this paper, we describe how diversity and divergence between closely related species change with time, using correlations between landscapes of genetic variation as a tool to understand the interplay between evolutionary processes. We find strong correlations between landscapes of diversity and divergence in a well-sampled set of great ape genomes, and explore how various processes such as incomplete lineage sorting, mutation rate variation, GC-biased gene conversion and selection contribute to these correlations. Through highly realistic, chromosome-scale, forward-in-time simulations, we show that the landscapes of diversity and divergence in the great apes are too well correlated to be explained via strictly neutral processes alone. Our best fitting simulation includes both deleterious and beneficial mutations in functional portions of the genome, in which 9% of fixations within those regions is driven by positive selection. This study provides a framework for modeling genetic variation in closely related species, an approach which can shed light on the complex balance of forces that have shaped genetic variation.
Collapse
Affiliation(s)
- Murillo F Rodrigues
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA
- Department of Biology, University of Oregon, Eugene, OR 97403, USA
| | - Andrew D Kern
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA
- Department of Biology, University of Oregon, Eugene, OR 97403, USA
| | - Peter L Ralph
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403, USA
- Department of Biology, University of Oregon, Eugene, OR 97403, USA
- Department of Mathematics, University of Oregon, Eugene, OR 97403, USA
| |
Collapse
|
5
|
Harris M, Kim BY, Garud N. Enrichment of hard sweeps on the X chromosome compared to autosomes in six Drosophila species. Genetics 2024; 226:iyae019. [PMID: 38366786 PMCID: PMC10990427 DOI: 10.1093/genetics/iyae019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 01/17/2024] [Accepted: 01/18/2024] [Indexed: 02/18/2024] Open
Abstract
The X chromosome, being hemizygous in males, is exposed one-third of the time increasing the visibility of new mutations to natural selection, potentially leading to different evolutionary dynamics than autosomes. Recently, we found an enrichment of hard selective sweeps over soft selective sweeps on the X chromosome relative to the autosomes in a North American population of Drosophila melanogaster. To understand whether this enrichment is a universal feature of evolution on the X chromosome, we analyze diversity patterns across 6 commonly studied Drosophila species. We find an increased proportion of regions with steep reductions in diversity and elevated homozygosity on the X chromosome compared to autosomes. To assess if these signatures are consistent with positive selection, we simulate a wide variety of evolutionary scenarios spanning variations in demography, mutation rate, recombination rate, background selection, hard sweeps, and soft sweeps and find that the diversity patterns observed on the X are most consistent with hard sweeps. Our findings highlight the importance of sex chromosomes in driving evolutionary processes and suggest that hard sweeps have played a significant role in shaping diversity patterns on the X chromosome across multiple Drosophila species.
Collapse
Affiliation(s)
- Mariana Harris
- Department of Computational Medicine, University of California Los Angeles, Los Angeles, CA 90095, USA
| | - Bernard Y Kim
- Department of Biology, Stanford University, Stanford, CA 94305, USA
| | - Nandita Garud
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
- Department of Human Genetics, University of California Los Angeles, Los Angeles, CA 90095, USA
| |
Collapse
|
6
|
Kreger J, Mooney JA, Shibata D, MacLean AL. Developmental hematopoietic stem cell variation explains clonal hematopoiesis later in life. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.02.583106. [PMID: 38496542 PMCID: PMC10942294 DOI: 10.1101/2024.03.02.583106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Clonal hematopoiesis becomes increasingly common with age, but its cause is enigmatic because driver mutations are often absent. Serial observations infer weak selection indicating variants are acquired much earlier in life with unexplained initial growth spurts. Here we use fluctuating CpG methylation as a lineage marker to track stem cell clonal dynamics of hematopoiesis. We show, via the shared prenatal circulation of monozygotic twins, that weak selection conferred by stem cell variation created before birth can reliably yield clonal hematopoiesis later in life. Theory indicates weak selection will lead to dominance given enough time and large enough population sizes. Human hematopoiesis satisfies both these conditions. Stochastic loss of weakly selected variants is naturally prevented by the expansion of stem cell lineages during development. The dominance of stem cell clones created before birth is supported by blood fluctuating CpG methylation patterns that exhibit low correlation between unrelated individuals but are highly correlated between many elderly monozygotic twins. Therefore, clonal hematopoiesis driven by weak selection in later life appears to reflect variation created before birth.
Collapse
Affiliation(s)
- Jesse Kreger
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
| | - Jazlyn A. Mooney
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
| | - Darryl Shibata
- Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Adam L. MacLean
- Department of Quantitative and Computational Biology, University of Southern California, Los Angeles, CA, USA
| |
Collapse
|
7
|
Kyriazis CC, Lohmueller KE. Constraining models of dominance for nonsynonymous mutations in the human genome. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.25.582010. [PMID: 38463985 PMCID: PMC10925099 DOI: 10.1101/2024.02.25.582010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Dominance is a fundamental parameter in genetics, determining the dynamics of natural selection on deleterious and beneficial mutations, the patterns of genetic variation in natural populations, and the severity of inbreeding depression in a population. Despite this importance, dominance parameters remain poorly known, particularly in humans or other non-model organisms. A key reason for this lack of information about dominance is that it is extremely challenging to disentangle the selection coefficient (s) of a mutation from its dominance coefficient (h). Here, we explore dominance and selection parameters in humans by fitting models to the site frequency spectrum (SFS) for nonsynonymous mutations. When assuming a single dominance coefficient for all nonsynonymous mutations, we find that numerous h values can fit the data, so long as h is greater than ~0.15. Moreover, we also observe that theoretically-predicted models with a negative relationship between h and s can also fit the data well, including models with h=0.05 for strongly deleterious mutations. Finally, we use our estimated dominance and selection parameters to inform simulations revisiting the question of whether the out-of-Africa bottleneck has led to differences in genetic load between African and non-African human populations. These simulations suggest that the relative burden of genetic load in non-African populations depends on the dominance model assumed, with slight increases for more weakly recessive models and slight decreases shown for more strongly recessive models. Moreover, these results also demonstrate that models of partially recessive nonsynonymous mutations can explain the observed severity of inbreeding depression in humans, bridging the gap between molecular population genetics and direct measures of fitness in humans. Our work represents a comprehensive assessment of dominance and deleterious variation in humans, with implications for parameterizing models of deleterious variation in humans and other mammalian species.
Collapse
Affiliation(s)
| | - Kirk E. Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, USA
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, USA
- Department of Human Genetics, David Geffen School of Medicine, Los Angeles, USA
| |
Collapse
|
8
|
Zurita AMI, Kyriazis CC, Lohmueller KE. The impact of non-neutral synonymous mutations when inferring selection on non-synonymous mutations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.07.579314. [PMID: 38370782 PMCID: PMC10871344 DOI: 10.1101/2024.02.07.579314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
The distribution of fitness effects (DFE) describes the proportions of new mutations that have different effects on reproductive fitness. Accurate measurements of the DFE are important because the DFE is a fundamental parameter in evolutionary genetics and has implications for our understanding of other phenomena like complex disease or inbreeding depression. Current computational methods to infer the DFE for nonsynonymous mutations from natural variation first estimate demographic parameters from synonymous variants to control for the effects of demography and background selection. Then, conditional on these parameters, the DFE is then inferred for nonsynonymous mutations. This approach relies on the assumption that synonymous variants are neutrally evolving. However, some evidence points toward synonymous mutations having measurable effects on fitness. To test whether selection on synonymous mutations affects inference of the DFE of nonsynonymous mutations, we simulated several possible models of selection on synonymous mutations using SLiM and attempted to recover the DFE of nonsynonymous mutations using Fit∂a∂i, a common method for DFE inference. Our results show that the presence of selection on synonymous variants leads to incorrect inferences of recent population growth. Furthermore, under certain parameter combinations, inferences of the DFE can have an inflated proportion of highly deleterious nonsynonymous mutations. However, this bias can be eliminated if the correct demographic parameters are used for DFE inference instead of the biased ones inferred from synonymous variants. Our work demonstrates how unmodeled selection on synonymous mutations may affect downstream inferences of the DFE.
Collapse
Affiliation(s)
- Aina Martinez I Zurita
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, USA
| | - Christopher C Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, USA
| | - Kirk E Lohmueller
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, USA
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, USA
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, USA
| |
Collapse
|
9
|
Ray DD, Flagel L, Schrider DR. IntroUNET: Identifying introgressed alleles via semantic segmentation. PLoS Genet 2024; 20:e1010657. [PMID: 38377104 PMCID: PMC10906877 DOI: 10.1371/journal.pgen.1010657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 03/01/2024] [Accepted: 01/29/2024] [Indexed: 02/22/2024] Open
Abstract
A growing body of evidence suggests that gene flow between closely related species is a widespread phenomenon. Alleles that introgress from one species into a close relative are typically neutral or deleterious, but sometimes confer a significant fitness advantage. Given the potential relevance to speciation and adaptation, numerous methods have therefore been devised to identify regions of the genome that have experienced introgression. Recently, supervised machine learning approaches have been shown to be highly effective for detecting introgression. One especially promising approach is to treat population genetic inference as an image classification problem, and feed an image representation of a population genetic alignment as input to a deep neural network that distinguishes among evolutionary models (i.e. introgression or no introgression). However, if we wish to investigate the full extent and fitness effects of introgression, merely identifying genomic regions in a population genetic alignment that harbor introgressed loci is insufficient-ideally we would be able to infer precisely which individuals have introgressed material and at which positions in the genome. Here we adapt a deep learning algorithm for semantic segmentation, the task of correctly identifying the type of object to which each individual pixel in an image belongs, to the task of identifying introgressed alleles. Our trained neural network is thus able to infer, for each individual in a two-population alignment, which of those individual's alleles were introgressed from the other population. We use simulated data to show that this approach is highly accurate, and that it can be readily extended to identify alleles that are introgressed from an unsampled "ghost" population, performing comparably to a supervised learning method tailored specifically to that task. Finally, we apply this method to data from Drosophila, showing that it is able to accurately recover introgressed haplotypes from real data. This analysis reveals that introgressed alleles are typically confined to lower frequencies within genic regions, suggestive of purifying selection, but are found at much higher frequencies in a region previously shown to be affected by adaptive introgression. Our method's success in recovering introgressed haplotypes in challenging real-world scenarios underscores the utility of deep learning approaches for making richer evolutionary inferences from genomic data.
Collapse
Affiliation(s)
- Dylan D. Ray
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Lex Flagel
- Division of Data Science, Gencove Inc., New York, New York, United States of America
- Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, Minnesota, United States of America
| | - Daniel R. Schrider
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| |
Collapse
|
10
|
Lucas-Sánchez M, Abdeli A, Bekada A, Calafell F, Benhassine T, Comas D. The Impact of Recent Demography on Functional Genetic Variation in North African Human Groups. Mol Biol Evol 2024; 41:msad283. [PMID: 38152862 PMCID: PMC10783648 DOI: 10.1093/molbev/msad283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 11/22/2023] [Accepted: 12/19/2023] [Indexed: 12/29/2023] Open
Abstract
The strategic location of North Africa has made the region the core of a wide range of human demographic events, including migrations, bottlenecks, and admixture processes. This has led to a complex and heterogeneous genetic and cultural landscape, which remains poorly studied compared to other world regions. Whole-exome sequencing is particularly relevant to determine the effects of these demographic events on current-day North Africans' genomes, since it allows to focus on those parts of the genome that are more likely to have direct biomedical consequences. Whole-exome sequencing can also be used to assess the effect of recent demography in functional genetic variation and the efficacy of natural selection, a long-lasting debate. In the present work, we use newly generated whole-exome sequencing and genome-wide array genotypes to investigate the effect of demography in functional variation in 7 North African populations, considering both cultural and demographic differences and with a special focus on Amazigh (plur. Imazighen) groups. We detect genetic differences among populations related to their degree of isolation and the presence of bottlenecks in their recent history. We find differences in the functional part of the genome that suggest a relaxation of purifying selection in the more isolated groups, allowing for an increase of putatively damaging variation. Our results also show a shift in mutational load coinciding with major demographic events in the region and reveal differences within and between cultural and geographic groups.
Collapse
Affiliation(s)
- Marcel Lucas-Sánchez
- Departament de Medicina i Ciències de la Vida, Institut de Biologia Evolutiva (CSIC-UPF), Universitat Pompeu Fabra, Barcelona, Spain
| | - Amine Abdeli
- Faculté des Sciences Biologiques, Laboratoire de Biologie Cellulaire et Moléculaire, Université des Sciences et de la Technologie Houari Boumediene, Alger, Algeria
| | - Asmahan Bekada
- Département de Biotechnologie, Faculté des Sciences de la Nature et de la Vie, Université Oran 1 (Ahmad Ben Bella), Oran, Algeria
| | - Francesc Calafell
- Departament de Medicina i Ciències de la Vida, Institut de Biologia Evolutiva (CSIC-UPF), Universitat Pompeu Fabra, Barcelona, Spain
| | - Traki Benhassine
- Faculté des Sciences Biologiques, Laboratoire de Biologie Cellulaire et Moléculaire, Université des Sciences et de la Technologie Houari Boumediene, Alger, Algeria
| | - David Comas
- Departament de Medicina i Ciències de la Vida, Institut de Biologia Evolutiva (CSIC-UPF), Universitat Pompeu Fabra, Barcelona, Spain
| |
Collapse
|
11
|
Harris M, Kim B, Garud N. Enrichment of hard sweeps on the X chromosome compared to autosomes in six Drosophila species. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.06.21.545888. [PMID: 38106201 PMCID: PMC10723260 DOI: 10.1101/2023.06.21.545888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
The X chromosome, being hemizygous in males, is exposed one third of the time increasing the visibility of new mutations to natural selection, potentially leading to different evolutionary dynamics than autosomes. Recently, we found an enrichment of hard selective sweeps over soft selective sweeps on the X chromosome relative to the autosomes in a North American population of Drosophila melanogaster. To understand whether this enrichment is a universal feature of evolution on the X chromosome, we analyze diversity patterns across six commonly studied Drosophila species. We find an increased proportion of regions with steep reductions in diversity and elevated homozygosity on the X chromosome compared to autosomes. To assess if these signatures are consistent with positive selection, we simulate a wide variety of evolutionary scenarios spanning variations in demography, mutation rate, recombination rate, background selection, hard sweeps, and soft sweeps, and find that the diversity patterns observed on the X are most consistent with hard sweeps. Our findings highlight the importance of sex chromosomes in driving evolutionary processes and suggest that hard sweeps have played a significant role in shaping diversity patterns on the X chromosome across multiple Drosophila species.
Collapse
Affiliation(s)
- Mariana Harris
- Department of Computational Medicine, University of California Los Angeles, Los Angeles California, United States of America
| | - Bernard Kim
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Nandita Garud
- Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles California, United States of America
- Department of Human Genetics, University of California, Los Angeles, California, United States of America
| |
Collapse
|
12
|
Kyriazis CC, Robinson JA, Lohmueller KE. Using Computational Simulations to Model Deleterious Variation and Genetic Load in Natural Populations. Am Nat 2023; 202:737-752. [PMID: 38033186 PMCID: PMC10897732 DOI: 10.1086/726736] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023]
Abstract
AbstractDeleterious genetic variation is abundant in wild populations, and understanding the ecological and conservation implications of such variation is an area of active research. Genomic methods are increasingly used to quantify the impacts of deleterious variation in natural populations; however, these approaches remain limited by an inability to accurately predict the selective and dominance effects of mutations. Computational simulations of deleterious variation offer a complementary tool that can help overcome these limitations, although such approaches have yet to be widely employed. In this perspective article, we aim to encourage ecological and conservation genomics researchers to adopt greater use of computational simulations to aid in deepening our understanding of deleterious variation in natural populations. We first provide an overview of the components of a simulation of deleterious variation, describing the key parameters involved in such models. Next, we discuss several approaches for validating simulation models. Finally, we compare and validate several recently proposed deleterious mutation models, demonstrating that models based on estimates of selection parameters from experimental systems are biased toward highly deleterious mutations. We describe a new model that is supported by multiple orthogonal lines of evidence and provide example scripts for implementing this model (https://github.com/ckyriazis/simulations_review).
Collapse
|
13
|
Mani S, Tlusty T. Gene birth in a model of non-genic adaptation. BMC Biol 2023; 21:257. [PMID: 37957718 PMCID: PMC10644530 DOI: 10.1186/s12915-023-01745-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Accepted: 10/24/2023] [Indexed: 11/15/2023] Open
Abstract
BACKGROUND Over evolutionary timescales, genomic loci can switch between functional and non-functional states through processes such as pseudogenization and de novo gene birth. Particularly, de novo gene birth is a widespread process, and many examples continue to be discovered across diverse evolutionary lineages. However, the general mechanisms that lead to functionalization are poorly understood, and estimated rates of de novo gene birth remain contentious. Here, we address this problem within a model that takes into account mutations and structural variation, allowing us to estimate the likelihood of emergence of new functions at non-functional loci. RESULTS Assuming biologically reasonable mutation rates and mutational effects, we find that functionalization of non-genic loci requires the realization of strict conditions. This is in line with the observation that most de novo genes are localized to the vicinity of established genes. Our model also provides an explanation for the empirical observation that emerging proto-genes are often lost despite showing signs of adaptation. CONCLUSIONS Our work elucidates the properties of non-genic loci that make them fertile for adaptation, and our results offer mechanistic insights into the process of de novo gene birth.
Collapse
Affiliation(s)
- Somya Mani
- Center for Soft and Living Matter, Institute for Basic Science, Ulsan 44919, Republic of Korea.
| | - Tsvi Tlusty
- Center for Soft and Living Matter, Institute for Basic Science, Ulsan 44919, Republic of Korea
- Departments of Physics and Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan 44919, Republic of Korea
| |
Collapse
|
14
|
Mah JC, Lohmueller KE, Garud N. Inference of the demographic histories and selective effects of human gut commensal microbiota over the course of human history. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.09.566454. [PMID: 38014007 PMCID: PMC10680615 DOI: 10.1101/2023.11.09.566454] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Despite the importance of gut commensal microbiota to human health, there is little knowledge about their evolutionary histories, including their population demographic histories and their distributions of fitness effects (DFE) of new mutations. Here, we infer the demographic histories and DFEs of 27 of the most highly prevalent and abundant commensal gut microbial species in North Americans over timescales exceeding human generations using a collection of lineages inferred from a panel of healthy hosts. We find overall reductions in genetic variation among commensal gut microbes sampled from a Western population relative to an African rural population. Additionally, some species in North American microbiomes display contractions in population size and others expansions, potentially occurring at several key historical moments in human history. DFEs across species vary from highly to mildly deleterious, with accessory genes experiencing more drift compared to core genes. Within genera, DFEs tend to be more congruent, reflective of underlying phylogenetic relationships. Taken together, these findings suggest that human commensal gut microbes have distinct evolutionary histories, possibly reflecting the unique roles of individual members of the microbiome.
Collapse
|
15
|
James J, Kastally C, Budde KB, González-Martínez SC, Milesi P, Pyhäjärvi T, Lascoux M. Between but Not Within-Species Variation in the Distribution of Fitness Effects. Mol Biol Evol 2023; 40:msad228. [PMID: 37832225 PMCID: PMC10630145 DOI: 10.1093/molbev/msad228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 09/04/2023] [Accepted: 09/25/2023] [Indexed: 10/15/2023] Open
Abstract
New mutations provide the raw material for evolution and adaptation. The distribution of fitness effects (DFE) describes the spectrum of effects of new mutations that can occur along a genome, and is, therefore, of vital interest in evolutionary biology. Recent work has uncovered striking similarities in the DFE between closely related species, prompting us to ask whether there is variation in the DFE among populations of the same species, or among species with different degrees of divergence, that is whether there is variation in the DFE at different levels of evolution. Using exome capture data from six tree species sampled across Europe we characterized the DFE for multiple species, and for each species, multiple populations, and investigated the factors potentially influencing the DFE, such as demography, population divergence, and genetic background. We find statistical support for the presence of variation in the DFE at the species level, even among relatively closely related species. However, we find very little difference at the population level, suggesting that differences in the DFE are primarily driven by deep features of species biology, and those evolutionarily recent events, such as demographic changes and local adaptation, have little impact.
Collapse
Affiliation(s)
- Jennifer James
- Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
- Swedish Collegium of Advanced Study, Uppsala University, Uppsala, Sweden
| | - Chedly Kastally
- Department of Forest Sciences, University of Helsinki, Helsinki, Finland
- Viikki Plant Science Centre, University of Helsinki, Helsinki, Finland
| | - Katharina B Budde
- Department of Forest Genetics and Forest Tree Breeding, Georg-August-University Goettingen, Goettingen, Germany
- Center of Biodiversity and Sustainable Land Use (CBL), University of Goettingen, Goettingen, Germany
| | - Santiago C González-Martínez
- National Research Institute for Agriculture, Food and the Environment (INRAE), University of Bordeaux, BIOGECO, Cestas, France
| | - Pascal Milesi
- Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
- Science for Life Laboratory (SciLifeLab), Uppsala University, Uppsala, Sweden
| | - Tanja Pyhäjärvi
- Department of Forest Sciences, University of Helsinki, Helsinki, Finland
- Viikki Plant Science Centre, University of Helsinki, Helsinki, Finland
| | - Martin Lascoux
- Department of Ecology and Genetics, Uppsala University, Uppsala, Sweden
| |
Collapse
|
16
|
Rodrigues MF, Kern AD, Ralph PL. Shared evolutionary processes shape landscapes of genomic variation in the great apes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.07.527547. [PMID: 36798346 PMCID: PMC9934647 DOI: 10.1101/2023.02.07.527547] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
For at least the past five decades population genetics, as a field, has worked to describe the precise balance of forces that shape patterns of variation in genomes. The problem is challenging because modelling the interactions between evolutionary processes is difficult, and different processes can impact genetic variation in similar ways. In this paper, we describe how diversity and divergence between closely related species change with time, using correlations between landscapes of genetic variation as a tool to understand the interplay between evolutionary processes. We find strong correlations between landscapes of diversity and divergence in a well sampled set of great ape genomes, and explore how various processes such as incomplete lineage sorting, mutation rate variation, GC-biased gene conversion and selection contribute to these correlations. Through highly realistic, chromosome-scale, forward-in-time simulations we show that the landscapes of diversity and divergence in the great apes are too well correlated to be explained via strictly neutral processes alone. Our best fitting simulation includes both deleterious and beneficial mutations in functional portions of the genome, in which 9% of fixations within those regions is driven by positive selection. This study provides a framework for modelling genetic variation in closely related species, an approach which can shed light on the complex balance of forces that have shaped genetic variation.
Collapse
Affiliation(s)
- Murillo F. Rodrigues
- Institute of Ecology and Evolution, University of Oregon
- Department of Biology, University of Oregon
| | - Andrew D. Kern
- Institute of Ecology and Evolution, University of Oregon
- Department of Biology, University of Oregon
| | - Peter L. Ralph
- Institute of Ecology and Evolution, University of Oregon
- Department of Biology, University of Oregon
- Department of Mathematics, University of Oregon
| |
Collapse
|
17
|
Dussex N, Tørresen OK, van der Valk T, Le Moullec M, Veiberg V, Tooming-Klunderud A, Skage M, Garmann-Aarhus B, Wood J, Rasmussen JA, Pedersen ÅØ, Martin SL, Røed KH, Jakobsen KS, Dalén L, Hansen BB, Martin MD. Adaptation to the High-Arctic island environment despite long-term reduced genetic variation in Svalbard reindeer. iScience 2023; 26:107811. [PMID: 37744038 PMCID: PMC10514459 DOI: 10.1016/j.isci.2023.107811] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 07/24/2023] [Accepted: 08/30/2023] [Indexed: 09/26/2023] Open
Abstract
Typically much smaller in number than their mainland counterparts, island populations are ideal systems to investigate genetic threats to small populations. The Svalbard reindeer (Rangifer tarandus platyrhynchus) is an endemic subspecies that colonized the Svalbard archipelago ca. 6,000-8,000 years ago and now shows numerous physiological and morphological adaptations to its arctic habitat. Here, we report a de-novo chromosome-level assembly for Svalbard reindeer and analyze 133 reindeer genomes spanning Svalbard and most of the species' Holarctic range, to examine the genomic consequences of long-term isolation and small population size in this insular subspecies. Empirical data, demographic reconstructions, and forward simulations show that long-term isolation and high inbreeding levels may have facilitated the reduction of highly deleterious-and to a lesser extent, moderately deleterious-variation. Our study indicates that long-term reduced genetic diversity did not preclude local adaptation to the High Arctic, suggesting that even severely bottlenecked populations can retain evolutionary potential.
Collapse
Affiliation(s)
- Nicolas Dussex
- Department of Natural History, University Museum, Norwegian University of Science and Technology (NTNU), Erling Skakkes gate 47A, Trondheim, Norway
| | - Ole K. Tørresen
- Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
| | - Tom van der Valk
- Centre for PalaeoGenetics, Svante Arrhenius väg 20C, SE 106 91 Stockholm, Sweden
- Department of Bioinformatics and Genetics, Swedish Museum of Natural History, SE 104 05 Stockholm, Sweden
| | - Mathilde Le Moullec
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology (NTNU), NO 7491 Trondheim, Norway
| | - Vebjørn Veiberg
- Department of Terrestrial Ecology, Norwegian Institute for Nature Research (NINA), NO 7034 Trondheim, Trondheim, Norway
| | - Ave Tooming-Klunderud
- Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
| | - Morten Skage
- Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
| | - Benedicte Garmann-Aarhus
- Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
- Natural History Museum, University of Oslo, NO 0318 Oslo, Norway
| | - Jonathan Wood
- Tree of Life, Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton CB10 1SA Cambridge, UK
| | - Jacob A. Rasmussen
- Department of Natural History, University Museum, Norwegian University of Science and Technology (NTNU), Erling Skakkes gate 47A, Trondheim, Norway
- Globe Institute, University of Copenhagen, 2100 Copenhagen, Denmark
| | | | - Sarah L.F. Martin
- Department of Natural History, University Museum, Norwegian University of Science and Technology (NTNU), Erling Skakkes gate 47A, Trondheim, Norway
| | - Knut H. Røed
- Department of Preclinical Sciences and Pathology, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway
| | - Kjetill S. Jakobsen
- Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, N-0316 Oslo, Norway
| | - Love Dalén
- Centre for PalaeoGenetics, Svante Arrhenius väg 20C, SE 106 91 Stockholm, Sweden
- Department of Bioinformatics and Genetics, Swedish Museum of Natural History, SE 104 05 Stockholm, Sweden
- Department of Zoology, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Brage B. Hansen
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology (NTNU), NO 7491 Trondheim, Norway
- Department of Terrestrial Ecology, Norwegian Institute for Nature Research (NINA), NO 7034 Trondheim, Trondheim, Norway
| | - Michael D. Martin
- Department of Natural History, University Museum, Norwegian University of Science and Technology (NTNU), Erling Skakkes gate 47A, Trondheim, Norway
- Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology (NTNU), NO 7491 Trondheim, Norway
| |
Collapse
|
18
|
Pivirotto AM, Platt A, Patel R, Kumar S, Hey J. Analyses of allele age and fitness impact reveal human beneficial alleles to be older than neutral controls. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.09.561569. [PMID: 37873438 PMCID: PMC10592680 DOI: 10.1101/2023.10.09.561569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
A classic population genetic prediction is that alleles experiencing directional selection should swiftly traverse allele frequency space, leaving detectable reductions in genetic variation in linked regions. However, despite this expectation, identifying clear footprints of beneficial allele passage has proven to be surprisingly challenging. We addressed the basic premise underlying this expectation by estimating the ages of large numbers of beneficial and deleterious alleles in a human population genomic data set. Deleterious alleles were found to be young, on average, given their allele frequency. However, beneficial alleles were older on average than non-coding, non-regulatory alleles of the same frequency. This finding is not consistent with directional selection and instead indicates some type of balancing selection. Among derived beneficial alleles, those fixed in the population show higher local recombination rates than those still segregating, consistent with a model in which new beneficial alleles experience an initial period of balancing selection due to linkage disequilibrium with deleterious recessive alleles. Alleles that ultimately fix following a period of balancing selection will leave a modest 'soft' sweep impact on the local variation, consistent with the overall paucity of species-wide 'hard' sweeps in human genomes.
Collapse
Affiliation(s)
| | - Alexander Platt
- Temple University, Department of Biology, Philadelphia PA 19122, USA
- University of Pennsylvania, Department of Genetics, Philadelphia PA 19104, USA
| | - Ravi Patel
- Temple University, Department of Biology, Philadelphia PA 19122, USA
- Institute for Genomics and Evolutionary Medicine, Temple University, PA 19122, USA
| | - Sudhir Kumar
- Temple University, Department of Biology, Philadelphia PA 19122, USA
- Institute for Genomics and Evolutionary Medicine, Temple University, PA 19122, USA
| | - Jody Hey
- Temple University, Department of Biology, Philadelphia PA 19122, USA
| |
Collapse
|
19
|
Nigenda-Morales SF, Lin M, Nuñez-Valencia PG, Kyriazis CC, Beichman AC, Robinson JA, Ragsdale AP, Urbán R J, Archer FI, Viloria-Gómora L, Pérez-Álvarez MJ, Poulin E, Lohmueller KE, Moreno-Estrada A, Wayne RK. The genomic footprint of whaling and isolation in fin whale populations. Nat Commun 2023; 14:5465. [PMID: 37699896 PMCID: PMC10497599 DOI: 10.1038/s41467-023-40052-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 07/10/2023] [Indexed: 09/14/2023] Open
Abstract
Twentieth century industrial whaling pushed several species to the brink of extinction, with fin whales being the most impacted. However, a small, resident population in the Gulf of California was not targeted by whaling. Here, we analyzed 50 whole-genomes from the Eastern North Pacific (ENP) and Gulf of California (GOC) fin whale populations to investigate their demographic history and the genomic effects of natural and human-induced bottlenecks. We show that the two populations diverged ~16,000 years ago, after which the ENP population expanded and then suffered a 99% reduction in effective size during the whaling period. In contrast, the GOC population remained small and isolated, receiving less than one migrant per generation. However, this low level of migration has been crucial for maintaining its viability. Our study exposes the severity of whaling, emphasizes the importance of migration, and demonstrates the use of genome-based analyses and simulations to inform conservation strategies.
Collapse
Affiliation(s)
- Sergio F Nigenda-Morales
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav), Irapuato, Guanajuato, 36824, Mexico.
- Department of Biological Sciences, California State University San Marcos, San Marcos, CA, 92096, USA.
| | - Meixi Lin
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
- Department of Plant Biology, Carnegie Institution for Science, Stanford, CA, 94305, USA.
| | - Paulina G Nuñez-Valencia
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav), Irapuato, Guanajuato, 36824, Mexico
- Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Christopher C Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Annabel C Beichman
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195, USA
| | - Jacqueline A Robinson
- Institute for Human Genetics, University of California, San Francisco (UCSF), San Francisco, CA, 94143, USA
| | - Aaron P Ragsdale
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav), Irapuato, Guanajuato, 36824, Mexico
- Department of Integrative Biology, University of Wisconsin, Madison, WI, 53706, USA
| | - Jorge Urbán R
- Departamento de Ciencias Marinas y Costeras, Universidad Autónoma de Baja California Sur (UABCS), La Paz, Baja California Sur, Mexico
| | - Frederick I Archer
- Marine Mammal and Turtle Division, Southwest Fisheries Science Center, La Jolla, CA, 92037, USA
| | - Lorena Viloria-Gómora
- Departamento de Ciencias Marinas y Costeras, Universidad Autónoma de Baja California Sur (UABCS), La Paz, Baja California Sur, Mexico
| | - María José Pérez-Álvarez
- Escuela de Medicina Veterinaria, Facultad de Medicina y Ciencias de la Salud, Universidad Mayor, Santiago, Chile
- Millennium Institute Biodiversity of Antarctic and Subantarctic Ecosystems (BASE), Universidad de Chile, Santiago, Chile
| | - Elie Poulin
- Millennium Institute Biodiversity of Antarctic and Subantarctic Ecosystems (BASE), Universidad de Chile, Santiago, Chile
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, CA, 90095, USA.
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
| | - Andrés Moreno-Estrada
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav), Irapuato, Guanajuato, 36824, Mexico.
| | - Robert K Wayne
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| |
Collapse
|
20
|
Charmouh AP, Bocedi G, Hartfield M. Inferring the distributions of fitness effects and proportions of strongly deleterious mutations. G3 (BETHESDA, MD.) 2023; 13:jkad140. [PMID: 37337692 PMCID: PMC10468728 DOI: 10.1093/g3journal/jkad140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 06/05/2023] [Accepted: 06/05/2023] [Indexed: 06/21/2023]
Abstract
The distribution of fitness effects is a key property in evolutionary genetics as it has implications for several evolutionary phenomena including the evolution of sex and mating systems, the rate of adaptive evolution, and the prevalence of deleterious mutations. Despite the distribution of fitness effects being extensively studied, the effects of strongly deleterious mutations are difficult to infer since such mutations are unlikely to be present in a sample of haplotypes, so genetic data may contain very little information about them. Recent work has attempted to correct for this issue by expanding the classic gamma-distributed model to explicitly account for strongly deleterious mutations. Here, we use simulations to investigate one such method, adding a parameter (plth) to capture the proportion of strongly deleterious mutations. We show that plth can improve the model fit when applied to individual species but underestimates the true proportion of strongly deleterious mutations. The parameter can also artificially maximize the likelihood when used to jointly infer a distribution of fitness effects from multiple species. As plth and related parameters are used in current inference algorithms, our results are relevant with respect to avoiding model artifacts and improving future tools for inferring the distribution of fitness effects.
Collapse
Affiliation(s)
- Anders P Charmouh
- School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3FX, UK
- Bioinformatics Research Centre Aarhus University, University City 81, building 1872, 3rd floor. DK-8000 Aarhus C, Denmark
| | - Greta Bocedi
- School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3FX, UK
| | - Matthew Hartfield
- Institute of Ecology and Evolution, The University of Edinburgh, Edinburgh EH9 3FL, UK
| |
Collapse
|
21
|
Cervantes S, Kesälahti R, Kumpula TA, Mattila TM, Helanterä H, Pyhäjärvi T. Strong Purifying Selection in Haploid Tissue-Specific Genes of Scots Pine Supports the Masking Theory. Mol Biol Evol 2023; 40:msad183. [PMID: 37565532 PMCID: PMC10457172 DOI: 10.1093/molbev/msad183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 06/16/2023] [Accepted: 08/10/2023] [Indexed: 08/12/2023] Open
Abstract
The masking theory states that genes expressed in a haploid stage will be under more efficient selection. In contrast, selection will be less efficient in genes expressed in a diploid stage, where the fitness effects of recessive deleterious or beneficial mutations can be hidden from selection in heterozygous form. This difference can influence several evolutionary processes such as the maintenance of genetic variation, adaptation rate, and genetic load. Masking theory expectations have been confirmed in single-cell haploid and diploid organisms. However, in multicellular organisms, such as plants, the effects of haploid selection are not clear-cut. In plants, the great majority of studies indicating haploid selection have been carried out using male haploid tissues in angiosperms. Hence, evidence in these systems is confounded with the effects of sexual selection and intraspecific competition. Evidence from other plant groups is scarce, and results show no support for the masking theory. Here, we have used a gymnosperm Scots pine megagametophyte, a maternally derived seed haploid tissue, and four diploid tissues to test the strength of purifying selection on a set of genes with tissue-specific expression. By using targeted resequencing data of those genes, we obtained estimates of genetic diversity, the site frequency spectrum of 0-fold and 4-fold sites, and inferred the distribution of fitness effects of new mutations in haploid and diploid tissue-specific genes. Our results show that purifying selection is stronger for tissue-specific genes expressed in the haploid megagametophyte tissue and that this signal of strong selection is not an artifact driven by high expression levels.
Collapse
Affiliation(s)
- Sandra Cervantes
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
- Biocenter Oulu, University of Oulu, Oulu, Finland
| | - Robert Kesälahti
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Timo A Kumpula
- Biocenter Oulu, University of Oulu, Oulu, Finland
- Laboratory of Cancer Genetics and Tumor Biology, Research Unit of Translational Medicine, University of Oulu, Oulu, Finland
| | - Tiina M Mattila
- Human Evolution, Department of Organismal Biology, Uppsala University, Uppsala, Sweden
| | - Heikki Helanterä
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Tanja Pyhäjärvi
- Department of Forest Sciences, University of Helsinki, Helsinki, Finland
| |
Collapse
|
22
|
Wade EE, Kyriazis CC, Cavassim MIA, Lohmueller KE. Quantifying the fraction of new mutations that are recessive lethal. Evolution 2023; 77:1539-1549. [PMID: 37074880 PMCID: PMC10309970 DOI: 10.1093/evolut/qpad061] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 03/21/2023] [Accepted: 04/14/2023] [Indexed: 04/20/2023]
Abstract
The presence and impact of recessive lethal mutations have been widely documented in diploid outcrossing species. However, precise estimates of the proportion of new mutations that are recessive lethal remain limited. Here, we evaluate the performance of Fit∂a∂i, a commonly used method for inferring the distribution of fitness effects (DFE), in the presence of lethal mutations. Using simulations, we demonstrate that in both additive and recessive cases, inference of the deleterious nonlethal portion of the DFE is minimally affected by a small proportion (<10%) of lethal mutations. Additionally, we demonstrate that while Fit∂a∂i cannot estimate the fraction of recessive lethal mutations, Fit∂a∂i can accurately infer the fraction of additive lethal mutations. Finally, as an alternative approach to estimate the proportion of mutations that are recessive lethal, we employ models of mutation-selection-drift balance using existing genomic parameters and estimates of segregating recessive lethals for humans and Drosophila melanogaster. In both species, the segregating recessive lethal load can be explained by a very small fraction (<1%) of new nonsynonymous mutations being recessive lethal. Our results refute recent assertions of a much higher proportion of mutations being recessive lethal (4%-5%), while highlighting the need for additional information on the joint distribution of selection and dominance coefficients.
Collapse
Affiliation(s)
- Emma E Wade
- Department of Ecology and Evolutionary Biology, University of California–Los Angeles, Los Angeles, CA, United States
- Department of Computer Science and Engineering, Mississippi State University, Starkville, MS, United States
| | - Christopher C Kyriazis
- Department of Ecology and Evolutionary Biology, University of California–Los Angeles, Los Angeles, CA, United States
| | - Maria Izabel A Cavassim
- Department of Ecology and Evolutionary Biology, University of California–Los Angeles, Los Angeles, CA, United States
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, University of California–Los Angeles, Los Angeles, CA, United States
- Interdepartmental Program in Bioinformatics, University of California–Los Angeles, Los Angeles, CA, United States
- Department of Human Genetics, David Geffen School of Medicine, University of California–Los Angeles, Los Angeles, CA, United States
| |
Collapse
|
23
|
Roberts M, Josephs EB. Weaker selection on genes with treatment-specific expression consistent with a limit on plasticity evolution in Arabidopsis thaliana. Genetics 2023; 224:iyad074. [PMID: 37094602 PMCID: PMC10484170 DOI: 10.1093/genetics/iyad074] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 03/06/2023] [Accepted: 04/07/2023] [Indexed: 04/26/2023] Open
Abstract
Differential gene expression between environments often underlies phenotypic plasticity. However, environment-specific expression patterns are hypothesized to relax selection on genes, and thus limit plasticity evolution. We collated over 27 terabases of RNA-sequencing data on Arabidopsis thaliana from over 300 peer-reviewed studies and 200 treatment conditions to investigate this hypothesis. Consistent with relaxed selection, genes with more treatment-specific expression have higher levels of nucleotide diversity and divergence at nonsynonymous sites but lack stronger signals of positive selection. This result persisted even after controlling for expression level, gene length, GC content, the tissue specificity of expression, and technical variation between studies. Overall, our investigation supports the existence of a hypothesized trade-off between the environment specificity of a gene's expression and the strength of selection on said gene in A. thaliana. Future studies should leverage multiple genome-scale datasets to tease apart the contributions of many variables in limiting plasticity evolution.
Collapse
Affiliation(s)
- Miles Roberts
- Genetics and Genome Sciences Program, Michigan State University, East Lansing, MI 48824, USA
| | - Emily B Josephs
- Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
- Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI 48824, USA
| |
Collapse
|
24
|
Johri P, Pfeifer SP, Jensen JD. Developing an evolutionary baseline model for humans: jointly inferring purifying selection with population history. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.11.536488. [PMID: 37090533 PMCID: PMC10120674 DOI: 10.1101/2023.04.11.536488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/25/2023]
Abstract
Building evolutionarily appropriate baseline models for natural populations is not only important for answering fundamental questions in population genetics - including quantifying the relative contributions of adaptive vs. non-adaptive processes - but it is also essential for identifying candidate loci experiencing relatively rare and episodic forms of selection ( e.g., positive or balancing selection). Here, a baseline model was developed for a human population of West African ancestry, the Yoruba, comprising processes constantly operating on the genome ( i.e. , purifying and background selection, population size changes, recombination rate heterogeneity, and gene conversion). Specifically, to perform joint inference of selective effects with demography, an approximate Bayesian approach was employed that utilizes the decay of background selection effects around functional elements, taking into account genomic architecture. This approach inferred a recent 6-fold population growth together with a distribution of fitness effects that is skewed towards effectively neutral mutations. Importantly, these results further suggest that, while strong and/or frequent recurrent positive selection is inconsistent with observed data, weak to moderate positive selection is consistent but unidentifiable if rare.
Collapse
|
25
|
Kyriazis CC, Robinson JA, Nigenda-Morales SF, Beichman AC, Rojas-Bracho L, Robertson KM, Fontaine MC, Wayne RK, Taylor BL, Lohmueller KE, Morin PA. Models based on best-available information support a low inbreeding load and potential for recovery in the vaquita. Heredity (Edinb) 2023; 130:183-187. [PMID: 36941409 PMCID: PMC10076335 DOI: 10.1038/s41437-023-00608-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 03/01/2023] [Accepted: 03/02/2023] [Indexed: 03/23/2023] Open
Affiliation(s)
- Christopher C Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Jacqueline A Robinson
- Institute for Human Genetics, University of California, San Francisco, San Francisco, CA, USA.
| | - Sergio F Nigenda-Morales
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav); Irapuato, Guanajuato, Mexico
| | - Annabel C Beichman
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | | | - Kelly M Robertson
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, CA, USA
| | - Michael C Fontaine
- MIVEGEC, Université de Montpellier, CNRS, IRD, Montpellier, France
- Centre de Recherche en Écologie et Évolution de la Santé (CREES), Montpellier, France
- Groningen Institute for Evolutionary Life Sciences (GELIFES), University of Groningen, Groningen, The Netherlands
| | - Robert K Wayne
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, USA
| | - Barbara L Taylor
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, CA, USA
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, USA.
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA.
| | - Phillip A Morin
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA, La Jolla, CA, USA.
| |
Collapse
|
26
|
Hewett AM, Stoffel MA, Peters L, Johnston SE, Pemberton JM. Selection, recombination and population history effects on runs of homozygosity (ROH) in wild red deer (Cervus elaphus). Heredity (Edinb) 2023; 130:242-250. [PMID: 36801920 PMCID: PMC10076382 DOI: 10.1038/s41437-023-00602-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Revised: 02/07/2023] [Accepted: 02/07/2023] [Indexed: 02/19/2023] Open
Abstract
The distribution of runs of homozygosity (ROH) may be shaped by a number of interacting processes such as selection, recombination and population history, but little is known about the importance of these mechanisms in shaping ROH in wild populations. We combined an empirical dataset of >3000 red deer genotyped at >35,000 genome-wide autosomal SNPs and evolutionary simulations to investigate the influence of each of these factors on ROH. We assessed ROH in a focal and comparison population to investigate the effect of population history. We investigated the role of recombination using both a physical map and a genetic linkage map to search for ROH. We found differences in ROH distribution between both populations and map types indicating that population history and local recombination rate have an effect on ROH. Finally, we ran forward genetic simulations with varying population histories, recombination rates and levels of selection, allowing us to further interpret our empirical data. These simulations showed that population history has a greater effect on ROH distribution than either recombination or selection. We further show that selection can cause genomic regions where ROH is common, only when the effective population size (Ne) is large or selection is particularly strong. In populations having undergone a population bottleneck, genetic drift can outweigh the effect of selection. Overall, we conclude that in this population, genetic drift resulting from a historical population bottleneck is most likely to have resulted in the observed ROH distribution, with selection possibly playing a minor role.
Collapse
Affiliation(s)
- Anna M Hewett
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK.
| | - Martin A Stoffel
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK
| | - Lucy Peters
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK
- GenPhySE, Université de Toulouse, INRAE, ENVT, 31326, Castanet-Tolosan, France
| | - Susan E Johnston
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK
| | - Josephine M Pemberton
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3FL, UK
| |
Collapse
|
27
|
Non-synonymous variation and protein structure of candidate genes associated with selection in farm and wild populations of turbot (Scophthalmus maximus). Sci Rep 2023; 13:3019. [PMID: 36810752 PMCID: PMC9944912 DOI: 10.1038/s41598-023-29826-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 02/10/2023] [Indexed: 02/24/2023] Open
Abstract
Non-synonymous variation (NSV) of protein coding genes represents raw material for selection to improve adaptation to the diverse environmental scenarios in wild and livestock populations. Many aquatic species face variations in temperature, salinity and biological factors throughout their distribution range that is reflected by the presence of allelic clines or local adaptation. The turbot (Scophthalmus maximus) is a flatfish of great commercial value with a flourishing aquaculture which has promoted the development of genomic resources. In this study, we developed the first atlas of NSVs in the turbot genome by resequencing 10 individuals from Northeast Atlantic Ocean. More than 50,000 NSVs where detected in the ~ 21,500 coding genes of the turbot genome, and we selected 18 NSVs to be genotyped using a single Mass ARRAY multiplex on 13 wild populations and three turbot farms. We detected signals of divergent selection on several genes related to growth, circadian rhythms, osmoregulation and oxygen binding in the different scenarios evaluated. Furthermore, we explored the impact of NSVs identified on the 3D structure and functional relationship of the correspondent proteins. In summary, our study provides a strategy to identify NSVs in species with consistently annotated and assembled genomes to ascertain their role in adaptation.
Collapse
|
28
|
Robinson J, Kyriazis CC, Yuan SC, Lohmueller KE. Deleterious Variation in Natural Populations and Implications for Conservation Genetics. Annu Rev Anim Biosci 2023; 11:93-114. [PMID: 36332644 PMCID: PMC9933137 DOI: 10.1146/annurev-animal-080522-093311] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Deleterious mutations decrease reproductive fitness and are ubiquitous in genomes. Given that many organisms face ongoing threats of extinction, there is interest in elucidating the impact of deleterious variation on extinction risk and optimizing management strategies accounting for such mutations. Quantifying deleterious variation and understanding the effects of population history on deleterious variation are complex endeavors because we do not know the strength of selection acting on each mutation. Further, the effect of demographic history on deleterious mutations depends on the strength of selection against the mutation and the degree of dominance. Here we clarify how deleterious variation can be quantified and studied in natural populations. We then discuss how different demographic factors, such as small population size, nonequilibrium population size changes, inbreeding, and gene flow, affect deleterious variation. Lastly, we provide guidance on studying deleterious variation in nonmodel populations of conservation concern.
Collapse
Affiliation(s)
- Jacqueline Robinson
- Institute for Human Genetics, University of California, San Francisco, California, USA;
| | - Christopher C Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, USA; , ,
| | - Stella C Yuan
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, USA; , ,
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, USA; , , .,Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California, USA
| |
Collapse
|
29
|
Kyriazis CC, Beichman AC, Brzeski KE, Hoy SR, Peterson RO, Vucetich JA, Vucetich LM, Lohmueller KE, Wayne RK. Genomic Underpinnings of Population Persistence in Isle Royale Moose. Mol Biol Evol 2023; 40:7024794. [PMID: 36729989 PMCID: PMC9927576 DOI: 10.1093/molbev/msad021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 01/20/2023] [Accepted: 01/25/2023] [Indexed: 02/03/2023] Open
Abstract
Island ecosystems provide natural laboratories to assess the impacts of isolation on population persistence. However, most studies of persistence have focused on a single species, without comparisons to other organisms they interact with in the ecosystem. The case study of moose and gray wolves on Isle Royale allows for a direct contrast of genetic variation in isolated populations that have experienced dramatically differing population trajectories over the past decade. Whereas the Isle Royale wolf population recently declined nearly to extinction due to severe inbreeding depression, the moose population has thrived and continues to persist, despite having low genetic diversity and being isolated for ∼120 years. Here, we examine the patterns of genomic variation underlying the continued persistence of the Isle Royale moose population. We document high levels of inbreeding in the population, roughly as high as the wolf population at the time of its decline. However, inbreeding in the moose population manifests in the form of intermediate-length runs of homozygosity suggestive of historical inbreeding and purging, contrasting with the long runs of homozygosity observed in the smaller wolf population. Using simulations, we confirm that substantial purging has likely occurred in the moose population. However, we also document notable increases in genetic load, which could eventually threaten population viability over the long term. Overall, our results demonstrate a complex relationship between inbreeding, genetic diversity, and population viability that highlights the use of genomic datasets and computational simulation tools for understanding the factors enabling persistence in isolated populations.
Collapse
Affiliation(s)
| | | | - Kristin E Brzeski
- College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
| | - Sarah R Hoy
- College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
| | - Rolf O Peterson
- College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
| | - John A Vucetich
- College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
| | - Leah M Vucetich
- College of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI
| | | | | |
Collapse
|
30
|
Zhang X, Kim B, Singh A, Sankararaman S, Durvasula A, Lohmueller KE. MaLAdapt Reveals Novel Targets of Adaptive Introgression From Neanderthals and Denisovans in Worldwide Human Populations. Mol Biol Evol 2023; 40:msad001. [PMID: 36617238 PMCID: PMC9887621 DOI: 10.1093/molbev/msad001] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 12/25/2022] [Accepted: 12/28/2022] [Indexed: 01/09/2023] Open
Abstract
Adaptive introgression (AI) facilitates local adaptation in a wide range of species. Many state-of-the-art methods detect AI with ad-hoc approaches that identify summary statistic outliers or intersect scans for positive selection with scans for introgressed genomic regions. Although widely used, approaches intersecting outliers are vulnerable to a high false-negative rate as the power of different methods varies, especially for complex introgression events. Moreover, population genetic processes unrelated to AI, such as background selection or heterosis, may create similar genomic signals to AI, compromising the reliability of methods that rely on neutral null distributions. In recent years, machine learning (ML) methods have been increasingly applied to population genetic questions. Here, we present a ML-based method called MaLAdapt for identifying AI loci from genome-wide sequencing data. Using an Extra-Trees Classifier algorithm, our method combines information from a large number of biologically meaningful summary statistics to capture a powerful composite signature of AI across the genome. In contrast to existing methods, MaLAdapt is especially well-powered to detect AI with mild beneficial effects, including selection on standing archaic variation, and is robust to non-AI selective sweeps, heterosis from deleterious mutations, and demographic misspecification. Furthermore, MaLAdapt outperforms existing methods for detecting AI based on the analysis of simulated data and the validation of empirical signals through visual inspection of haplotype patterns. We apply MaLAdapt to the 1000 Genomes Project human genomic data and discover novel AI candidate regions in non-African populations, including genes that are enriched in functionally important biological pathways regulating metabolism and immune responses.
Collapse
Affiliation(s)
- Xinjun Zhang
- Department of Ecology and Evolutionary Biology, UCLA, Los Angeles, CA
| | - Bernard Kim
- Department of Biology, Stanford University, Palo Alto, CA
| | - Armaan Singh
- Department of Computer Science, UCLA, Los Angeles, CA
| | - Sriram Sankararaman
- Department of Computer Science, UCLA, Los Angeles, CA
- Department of Computational Medicine, UCLA, Los Angeles, CA
- Department of Human Genetics, David Geffen School of Medicine, UCLA, Los Angeles, CA
| | - Arun Durvasula
- Department of Genetics, Harvard Medical School, Boston, MA
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, UCLA, Los Angeles, CA
- Department of Human Genetics, David Geffen School of Medicine, UCLA, Los Angeles, CA
| |
Collapse
|
31
|
Angst P, Ameline C, Haag CR, Ben-Ami F, Ebert D, Fields PD. Genetic Drift Shapes the Evolution of a Highly Dynamic Metapopulation. Mol Biol Evol 2022; 39:6874788. [PMID: 36472514 PMCID: PMC9778854 DOI: 10.1093/molbev/msac264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 11/28/2022] [Accepted: 12/01/2022] [Indexed: 12/12/2022] Open
Abstract
The dynamics of extinction and (re)colonization in habitat patches are characterizing features of dynamic metapopulations, causing them to evolve differently than large, stable populations. The propagule model, which assumes genetic bottlenecks during colonization, posits that newly founded subpopulations have low genetic diversity and are genetically highly differentiated from each other. Immigration may then increase diversity and decrease differentiation between subpopulations. Thus, older and/or less isolated subpopulations are expected to have higher genetic diversity and less genetic differentiation. We tested this theory using whole-genome pool-sequencing to characterize nucleotide diversity and differentiation in 60 subpopulations of a natural metapopulation of the cyclical parthenogen Daphnia magna. For comparison, we characterized diversity in a single, large, and stable D. magna population. We found reduced (synonymous) genomic diversity, a proxy for effective population size, weak purifying selection, and low rates of adaptive evolution in the metapopulation compared with the large, stable population. These differences suggest that genetic bottlenecks during colonization reduce effective population sizes, which leads to strong genetic drift and reduced selection efficacy in the metapopulation. Consistent with the propagule model, we found lower diversity and increased differentiation in younger and also in more isolated subpopulations. Our study sheds light on the genomic consequences of extinction-(re)colonization dynamics to an unprecedented degree, giving strong support for the propagule model. We demonstrate that the metapopulation evolves differently from a large, stable population and that evolution is largely driven by genetic drift.
Collapse
Affiliation(s)
| | - Camille Ameline
- Department of Environmental Sciences, Zoology, University of Basel, Basel 4051, Switzerland,Evolutionary Biology, Instituto Gulbenkian de Ciência, Oeiras 2780-156, Portugal
| | - Christoph R Haag
- CEFE, Université de Montpellier, CNRS, EPHE, IRD, Montpellier 34293, France,Tvärminne Zoological Station, University of Helsinki, Hanko 10900, Finland
| | - Frida Ben-Ami
- Tvärminne Zoological Station, University of Helsinki, Hanko 10900, Finland,George S. Wise Faculty of Life Sciences, School of Zoology, Tel Aviv University, Tel Aviv 69978, Israel
| | - Dieter Ebert
- Department of Environmental Sciences, Zoology, University of Basel, Basel 4051, Switzerland,Tvärminne Zoological Station, University of Helsinki, Hanko 10900, Finland
| | - Peter D Fields
- Department of Environmental Sciences, Zoology, University of Basel, Basel 4051, Switzerland,Tvärminne Zoological Station, University of Helsinki, Hanko 10900, Finland
| |
Collapse
|
32
|
Lye Z, Choi JY, Purugganan MD. Deleterious mutations and the rare allele burden on rice gene expression. Mol Biol Evol 2022; 39:6693943. [PMID: 36073358 PMCID: PMC9512150 DOI: 10.1093/molbev/msac193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Deleterious genetic variation is maintained in populations at low frequencies. Under a model of stabilizing selection, rare (and presumably deleterious) genetic variants are associated with increase or decrease in gene expression from some intermediate optimum. We investigate this phenomenon in a population of largely Oryza sativa ssp. indica rice landraces under normal unstressed wet and stressful drought field conditions. We include single nucleotide polymorphisms, insertion/deletion mutations, and structural variants in our analysis and find a stronger association between rare variants and gene expression outliers under the stress condition. We also show an association of the strength of this rare variant effect with linkage, gene expression levels, network connectivity, local recombination rate, and fitness consequence scores, consistent with the stabilizing selection model of gene expression.
Collapse
Affiliation(s)
- Zoe Lye
- Center for Genomics and Systems Biology, New York University, New York, NY 10003
| | - Jae Young Choi
- Center for Genomics and Systems Biology, New York University, New York, NY 10003
| | - Michael D Purugganan
- Center for Genomics and Systems Biology, New York University, New York, NY 10003.,Center for Genomics and Systems Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| |
Collapse
|
33
|
Johri P, Gout JF, Doak TG, Lynch M. A Population-Genetic Lens into the Process of Gene Loss Following Whole-Genome Duplication. Mol Biol Evol 2022; 39:6594306. [PMID: 35639978 PMCID: PMC9206413 DOI: 10.1093/molbev/msac118] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Whole-genome duplications (WGDs) have occurred in many eukaryotic lineages. However, the underlying evolutionary forces and molecular mechanisms responsible for the long-term retention of gene duplicates created by WGDs are not well understood. We employ a population-genomic approach to understand the selective forces acting on paralogs and investigate ongoing duplicate-gene loss in multiple species of Paramecium that share an ancient WGD. We show that mutations that abolish protein function are more likely to be segregating in retained WGD paralogs than in single-copy genes, most likely because of ongoing nonfunctionalization post-WGD. This relaxation of purifying selection occurs in only one WGD paralog, accompanied by the gradual fixation of nonsynonymous mutations and reduction in levels of expression, and occurs over a long period of evolutionary time, “marking” one locus for future loss. Concordantly, the fitness effects of new nonsynonymous mutations and frameshift-causing indels are significantly more deleterious in the highly expressed copy compared with their paralogs with lower expression. Our results provide a novel mechanistic model of gene duplicate loss following WGDs, wherein selection acts on the sum of functional activity of both duplicate genes, allowing the two to wander in expression and functional space, until one duplicate locus eventually degenerates enough in functional efficiency or expression that its contribution to total activity is too insignificant to be retained by purifying selection. Retention of duplicates by such mechanisms predicts long times to duplicate-gene loss, which should not be falsely attributed to retention due to gain/change in function.
Collapse
Affiliation(s)
- Parul Johri
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Jean-Francois Gout
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS 39762, USA
| | - Thomas G Doak
- Department of Biology, Indiana University, Bloomington, IN 47405, USA.,National Center for Genome Analysis Support, Indiana University, Bloomington, IN 47405, USA
| | - Michael Lynch
- Center for Mechanisms of Evolution, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| |
Collapse
|
34
|
A natural mutator allele shapes mutation spectrum variation in mice. Nature 2022; 605:497-502. [PMID: 35545679 DOI: 10.1038/s41586-022-04701-5] [Citation(s) in RCA: 29] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 03/25/2022] [Indexed: 12/12/2022]
Abstract
Although germline mutation rates and spectra can vary within and between species, common genetic modifiers of the mutation rate have not been identified in nature1. Here we searched for loci that influence germline mutagenesis using a uniquely powerful resource: a panel of recombinant inbred mouse lines known as the BXD, descended from the laboratory strains C57BL/6J (B haplotype) and DBA/2J (D haplotype). Each BXD lineage has been maintained by brother-sister mating in the near absence of natural selection, accumulating de novo mutations for up to 50 years on a known genetic background that is a unique linear mosaic of B and D haplotypes2. We show that mice inheriting D haplotypes at a quantitative trait locus on chromosome 4 accumulate C>A germline mutations at a 50% higher rate than those inheriting B haplotypes, primarily owing to the activity of a C>A-dominated mutational signature known as SBS18. The B and D quantitative trait locus haplotypes encode different alleles of Mutyh, a DNA repair gene that underlies the heritable cancer predisposition syndrome that causes colorectal tumors with a high SBS18 mutation load3,4. Both B and D Mutyh alleles are present in wild populations of Mus musculus domesticus, providing evidence that common genetic variation modulates germline mutagenesis in a model mammalian species.
Collapse
|
35
|
Robinson JA, Kyriazis CC, Nigenda-Morales SF, Beichman AC, Rojas-Bracho L, Robertson KM, Fontaine MC, Wayne RK, Lohmueller KE, Taylor BL, Morin PA. The critically endangered vaquita is not doomed to extinction by inbreeding depression. Science 2022; 376:635-639. [PMID: 35511971 PMCID: PMC9881057 DOI: 10.1126/science.abm1742] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In cases of severe wildlife population decline, a key question is whether recovery efforts will be impeded by genetic factors, such as inbreeding depression. Decades of excess mortality from gillnet fishing have driven Mexico's vaquita porpoise (Phocoena sinus) to ~10 remaining individuals. We analyzed whole-genome sequences from 20 vaquitas and integrated genomic and demographic information into stochastic, individual-based simulations to quantify the species' recovery potential. Our analysis suggests that the vaquita's historical rarity has resulted in a low burden of segregating deleterious variation, reducing the risk of inbreeding depression. Similarly, genome-informed simulations suggest that the vaquita can recover if bycatch mortality is immediately halted. This study provides hope for vaquitas and other naturally rare endangered species and highlights the utility of genomics in predicting extinction risk.
Collapse
Affiliation(s)
- Jacqueline A. Robinson
- Institute for Human Genetics, University of California, San Francisco; San Francisco, CA, USA
| | - Christopher C. Kyriazis
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles; Los Angeles, CA, USA
| | - Sergio F. Nigenda-Morales
- Advanced Genomics Unit, National Laboratory of Genomics for Biodiversity (Langebio), Center for Research and Advanced Studies (Cinvestav); Irapuato, Guanajuato, Mexico
| | | | - Lorenzo Rojas-Bracho
- Comisión Nacional de Áreas Naturales Protegidas/SEMARNAT; Ensenada, Mexico
- PNUD-Sinergia en la Comisión Nacional de Áreas Naturales Protegidas, Ensenada, B.C., México
| | - Kelly M. Robertson
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA ; La Jolla, CA, USA
| | - Michael C. Fontaine
- MIVEGEC, Université de Montpellier, CNRS, IRD; Montpellier, France
- Centre de Recherche en Écologie et Évolution de la Santé (CREES); Montpellier, France
- Groningen Institute for Evolutionary Life Sciences (GELIFES), University of Groningen; Groningen, The Netherlands
| | - Robert K. Wayne
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles; Los Angeles, CA, USA
| | - Kirk E. Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles; Los Angeles, CA, USA
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles; Los Angeles, CA, USA
| | - Barbara L. Taylor
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA ; La Jolla, CA, USA
| | - Phillip A. Morin
- Southwest Fisheries Science Center, National Marine Fisheries Service, NOAA ; La Jolla, CA, USA
| |
Collapse
|
36
|
Fields PD, McTaggart S, Reisser CMO, Haag C, Palmer WH, Little TJ, Ebert D, Obbard DJ. Population-genomic analysis identifies a low rate of global adaptive fixation in the proteins of the cyclical parthenogen Daphnia magna. Mol Biol Evol 2022; 39:6542319. [PMID: 35244177 PMCID: PMC8963301 DOI: 10.1093/molbev/msac048] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Daphnia are well-established ecological and evolutionary models, and the interaction between D. magna and its microparasites is widely considered a paragon of the host-parasite coevolutionary process. Like other well-studied arthropods such as Drosophila melanogaster and Anopheles gambiae, D. magna is a small, widespread, and abundant species that is therefore expected to display a large long-term population size and high rates of adaptive protein evolution. However, unlike these other species, D. magna is cyclically asexual and lives in a highly structured environment (ponds and lakes) with moderate levels of dispersal, both of which are predicted to impact upon long-term effective population size and adaptive protein evolution. To investigate patterns of adaptive protein fixation, we produced the complete coding genomes of 36 D. magna clones sampled from across the European range (Western Palaearctic), along with draft sequences for the close relatives D. similis and D. lumholtzi, used as outgroups. We analyzed genome-wide patterns of adaptive fixation, with a particular focus on genes that have an a priori expectation of high rates, such as those likely to mediate immune responses, RNA interference against viruses and transposable elements, and those with a strongly male-biased expression pattern. We find that, as expected, D. magna displays high levels of diversity and that this is highly structured among populations. However, compared with Drosophila, we find that D. magna proteins appear to have a high proportion of weakly deleterious variants and do not show evidence of pervasive adaptive fixation across its entire range. This is true of the genome as a whole, and also of putative ‘arms race’ genes that often show elevated levels of adaptive substitution in other species. In addition to the likely impact of extensive, and previously documented, local adaptation, we speculate that these findings may reflect reduced efficacy of selection associated with cyclical asexual reproduction.
Collapse
Affiliation(s)
- Peter D Fields
- University of Basel, Department of Environmental Sciences, Zoology, Vesalgasse 1, Basel, CH-4051, Switzerland
| | - Seanna McTaggart
- Institute of Evolutionary Biology; School of Biological Sciences University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom
| | - Céline M O Reisser
- Centre d'Ecologie Fonctionnelle et Evolutive CEFE UMR 5175, Univ Montpellier, CNRS, EPHE, IRD, Univ Paul Valéry Montpellier 3, campus CNRS, 1919, route de Mende, 34293 Montpellier Cedex 5, France.,MARBEC, Univ Montpellier, CNRS, IFREMER, IRD, Montpellier, France
| | - Christoph Haag
- Centre d'Ecologie Fonctionnelle et Evolutive CEFE UMR 5175, Univ Montpellier, CNRS, EPHE, IRD, Univ Paul Valéry Montpellier 3, campus CNRS, 1919, route de Mende, 34293 Montpellier Cedex 5, France
| | - William H Palmer
- Institute of Evolutionary Biology; School of Biological Sciences University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom
| | - Tom J Little
- Institute of Evolutionary Biology; School of Biological Sciences University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom
| | - Dieter Ebert
- University of Basel, Department of Environmental Sciences, Zoology, Vesalgasse 1, Basel, CH-4051, Switzerland
| | - Darren J Obbard
- Institute of Evolutionary Biology; School of Biological Sciences University of Edinburgh, Edinburgh, EH9 3JT, United Kingdom
| |
Collapse
|
37
|
Vecchyo DOD, Lohmueller KE, Novembre J. Haplotype-based inference of the distribution of fitness effects. Genetics 2022; 220:6501446. [PMID: 35100400 PMCID: PMC8982047 DOI: 10.1093/genetics/iyac002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 12/18/2021] [Indexed: 11/13/2022] Open
Abstract
Abstract
Recent genome sequencing studies with large sample sizes in humans have discovered a vast quantity of low-frequency variants, providing an important source of information to analyze how selection is acting on human genetic variation. In order to estimate the strength of natural selection acting on low-frequency variants, we have developed a likelihood-based method that uses the lengths of pairwise identity-by-state between haplotypes carrying low-frequency variants. We show that in some non-equilibrium populations (such as those that have had recent population expansions) it is possible to distinguish between positive or negative selection acting on a set of variants. With our new framework, one can infer a fixed selection intensity acting on a set of variants at a particular frequency, or a distribution of selection coefficients for standing variants and new mutations. We show an application of our method to the UK10K phased haplotype dataset of individuals.
Collapse
Affiliation(s)
- Diego Ortega-Del Vecchyo
- Laboratorio Internacional de Investigación sobre el Genoma Humano, Universidad Nacional Autónoma de México, Juriquilla, Querétaro, 76230, México
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, Los Angeles, California, 90095, United States of America
| | - Kirk E Lohmueller
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, Los Angeles, California, 90095, United States of America
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, 90095, United States of America
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, 90095, United States of America
| | - John Novembre
- Department of Human Genetics, University of Chicago, Chicago, Illinois, 60637, United States of America
- Department of Ecology and Evolution, University of Chicago, Chicago, Illinois, 60637, United States of America
| |
Collapse
|
38
|
Xie HX, Liang XX, Chen ZQ, Li WM, Mi CR, Li M, Wu ZJ, Zhou XM, Du WG. Ancient demographics determine the effectiveness of genetic purging in endangered lizards. Mol Biol Evol 2021; 39:6468625. [PMID: 34919713 PMCID: PMC8788223 DOI: 10.1093/molbev/msab359] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The purging of deleterious alleles has been hypothesized to mitigate inbreeding depression, but its effectiveness in endangered species remains debatable. To understand how deleterious alleles are purged during population contractions, we analyzed genomes of the endangered Chinese crocodile lizard (Shinisaurus crocodilurus), which is the only surviving species of its family and currently isolated into small populations. Population genomic analyses revealed four genetically distinct conservation units and sharp declines in both effective population size and genetic diversity. By comparing the relative genetic load across populations and conducting genomic simulations, we discovered that seriously deleterious alleles were effectively purged during population contractions in this relict species, although inbreeding generally enhanced the genetic burden. However, despite with the initial purging, our simulations also predicted that seriously deleterious alleles will gradually accumulate under prolonged bottlenecking. Therefore, we emphasize the importance of maintaining a minimum population capacity and increasing the functional genetic diversity in conservation efforts to preserve populations of the crocodile lizard and other endangered species.
Collapse
Affiliation(s)
- Hong-Xin Xie
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xi-Xi Liang
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
| | - Zhi-Qiang Chen
- Novogene Bioinformatics Institute, Beijing, 100083, China
| | - Wei-Ming Li
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Chun-Rong Mi
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Ming Li
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
| | - Zheng-Jun Wu
- Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection, Ministry of Education (Guangxi Normal University, Guilin, 541004, China ).,Guangxi Key Laboratory of Rare and Endangered Animal Ecology, College of Life Science, Guangxi Normal University, Guilin, 541006, China
| | - Xu-Ming Zhou
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
| | - Wei-Guo Du
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
| |
Collapse
|
39
|
Khan A, Patel K, Shukla H, Viswanathan A, van der Valk T, Borthakur U, Nigam P, Zachariah A, Jhala YV, Kardos M, Ramakrishnan U. Genomic evidence for inbreeding depression and purging of deleterious genetic variation in Indian tigers. Proc Natl Acad Sci U S A 2021; 118:e2023018118. [PMID: 34848534 PMCID: PMC8670471 DOI: 10.1073/pnas.2023018118] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/11/2021] [Indexed: 01/03/2023] Open
Abstract
Increasing habitat fragmentation leads to wild populations becoming small, isolated, and threatened by inbreeding depression. However, small populations may be able to purge recessive deleterious alleles as they become expressed in homozygotes, thus reducing inbreeding depression and increasing population viability. We used whole-genome sequences from 57 tigers to estimate individual inbreeding and mutation load in a small-isolated and two large-connected populations in India. As expected, the small-isolated population had substantially higher average genomic inbreeding (FROH = 0.57) than the large-connected (FROH = 0.35 and FROH = 0.46) populations. The small-isolated population had the lowest loss-of-function mutation load, likely due to purging of highly deleterious recessive mutations. The large populations had lower missense mutation loads than the small-isolated population, but were not identical, possibly due to different demographic histories. While the number of the loss-of-function alleles in the small-isolated population was lower, these alleles were at higher frequencies and homozygosity than in the large populations. Together, our data and analyses provide evidence of 1) high mutation load, 2) purging, and 3) the highest predicted inbreeding depression, despite purging, in the small-isolated population. Frequency distributions of damaging and neutral alleles uncover genomic evidence that purifying selection has removed part of the mutation load across Indian tiger populations. These results provide genomic evidence for purifying selection in both small and large populations, but also suggest that the remaining deleterious alleles may have inbreeding-associated fitness costs. We suggest that genetic rescue from sources selected based on genome-wide differentiation could offset any possible impacts of inbreeding depression.
Collapse
Affiliation(s)
- Anubhab Khan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India;
| | - Kaushalkumar Patel
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Harsh Shukla
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Ashwin Viswanathan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
- Nature Conservation Foundation, Mysore 570017, India
| | | | | | - Parag Nigam
- Wildlife Institute of India, Dehradun 248001, India
| | | | | | - Marty Kardos
- Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, WA 98112;
| | - Uma Ramakrishnan
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India;
- Department of Biotechnology-Wellcome Trust India Alliance, Hyderabad 500034, India
| |
Collapse
|
40
|
Sohail M, Izarraras-Gomez A, Ortega-Del Vecchyo D. Populations, Traits, and Their Spatial Structure in Humans. Genome Biol Evol 2021; 13:evab272. [PMID: 34894236 PMCID: PMC8715524 DOI: 10.1093/gbe/evab272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/06/2021] [Indexed: 11/16/2022] Open
Abstract
The spatial distribution of genetic variants is jointly determined by geography, past demographic processes, natural selection, and its interplay with environmental variation. A fraction of these genetic variants are "causal alleles" that affect the manifestation of a complex trait. The effect exerted by these causal alleles on complex traits can be independent or dependent on the environment. Understanding the evolutionary processes that shape the spatial structure of causal alleles is key to comprehend the spatial distribution of complex traits. Natural selection, past population size changes, range expansions, consanguinity, assortative mating, archaic introgression, admixture, and the environment can alter the frequencies, effect sizes, and heterozygosities of causal alleles. This provides a genetic axis along which complex traits can vary. However, complex traits also vary along biogeographical and sociocultural axes which are often correlated with genetic axes in complex ways. The purpose of this review is to consider these genetic and environmental axes in concert and examine the ways they can help us decipher the variation in complex traits that is visible in humans today. This initiative necessarily implies a discussion of populations, traits, the ability to infer and interpret "genetic" components of complex traits, and how these have been impacted by adaptive events. In this review, we provide a history-aware discussion on these topics using both the recent and more distant past of our academic discipline and its relevant contexts.
Collapse
Affiliation(s)
- Mashaal Sohail
- Department of Human Genetics, University of Chicago, USA
- Centro de Ciencias Genómicas (CCG), Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Alan Izarraras-Gomez
- Laboratorio Internacional de Investigación sobre el Genoma Humano (LIIGH), Universidad Nacional Autónoma de México (UNAM), Juriquilla, Querétaro, México
| | - Diego Ortega-Del Vecchyo
- Laboratorio Internacional de Investigación sobre el Genoma Humano (LIIGH), Universidad Nacional Autónoma de México (UNAM), Juriquilla, Querétaro, México
| |
Collapse
|
41
|
Ruzicka F, Connallon T, Reuter M. Sex differences in deleterious mutational effects in Drosophila melanogaster: combining quantitative and population genetic insights. Genetics 2021; 219:6362879. [PMID: 34740242 DOI: 10.1093/genetics/iyab143] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2021] [Accepted: 08/25/2021] [Indexed: 11/14/2022] Open
Abstract
Fitness effects of deleterious mutations can differ between females and males due to: (i) sex differences in the strength of purifying selection; and (ii) sex differences in ploidy. Although sex differences in fitness effects have important broader implications (e.g., for the evolution of sex and lifespan), few studies have quantified their scope. Those that have belong to one of two distinct empirical traditions: (i) quantitative genetics, which focusses on multi-locus genetic variances in each sex, but is largely agnostic about their genetic basis; and (ii) molecular population genetics, which focusses on comparing autosomal and X-linked polymorphism, but is poorly suited for inferring contemporary sex differences. Here, we combine both traditions to present a comprehensive analysis of female and male adult reproductive fitness among 202 outbred, laboratory-adapted, hemiclonal genomes of Drosophila melanogaster. While we find no clear evidence for sex differences in the strength of purifying selection, sex differences in ploidy generate multiple signals of enhanced purifying selection for X-linked loci. These signals are present in quantitative genetic metrics-i.e., a disproportionate contribution of the X to male (but not female) fitness variation-and population genetic metrics-i.e., steeper regressions of an allele's average fitness effect on its frequency, and proportionally less nonsynonymous polymorphism on the X than autosomes. Fitting our data to models for both sets of metrics, we infer that deleterious alleles are partially recessive. Given the often-large gap between quantitative and population genetic estimates of evolutionary parameters, our study showcases the benefits of combining genomic and fitness data when estimating such parameters.
Collapse
Affiliation(s)
- Filip Ruzicka
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton 3800, VIC, Australia.,Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK
| | - Tim Connallon
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton 3800, VIC, Australia
| | - Max Reuter
- Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK.,Centre for Life's Origins and Evolution, University College London, London WC1E 6BT, UK
| |
Collapse
|
42
|
Connallon T, Olito C. Natural selection and the distribution of chromosomal inversion lengths. Mol Ecol 2021; 31:3627-3641. [PMID: 34297880 DOI: 10.1111/mec.16091] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 07/16/2021] [Accepted: 07/19/2021] [Indexed: 11/28/2022]
Abstract
Chromosomal inversions contribute substantially to genome evolution, yet the processes governing their evolutionary dynamics remain poorly understood. Theory suggests that a readily measurable property of inversions-their length-can potentially affect their evolutionary fates. Emerging data on the lengths of polymorphic and fixed inversions may therefore provide clues to the evolutionary processes promoting inversion establishment. However, formal predictions for the distribution of inversion lengths remain incomplete, making empirical patterns difficult to interpret. We model the relation between inversion length and establishment probability for four inversion types: (1) neutral, (2) underdominant, (3) directly beneficial, and (4) indirectly beneficial, with selection favouring the latter because they capture locally adapted alleles at migration-selection balance and suppress recombination between them. We also consider how deleterious mutations affect the lengths of established inversions. We show that length distributions of common polymorphic and fixed inversions systematically differ among inversion types. Small rearrangements contribute the most to genome evolution under neutral and underdominant scenarios of selection, with the lengths of neutral inversion substitutions increasing, and those of underdominant substitutions decreasing, with effective population size. Among directly beneficial inversions, small rearrangements are preferentially fixed, whereas intermediate-to-large inversions are maintained as balanced polymorphisms via associative overdominance. Finally, inversions established under the local adaptation scenario are predominantly intermediate-to-large. Such inversions remain polymorphic or approach fixation within the local populations where they are favoured. Our models clarify how inversion length distributions relate to processes of inversion establishment, providing a platform for testing how natural selection shapes the evolution of genome structure.
Collapse
Affiliation(s)
- Tim Connallon
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton, Victoria, Australia
| | - Colin Olito
- Department of Biology, Section for Evolutionary Ecology, Lund University, Lund, Sweden
| |
Collapse
|
43
|
Garcia JA, Lohmueller KE. Negative linkage disequilibrium between amino acid changing variants reveals interference among deleterious mutations in the human genome. PLoS Genet 2021; 17:e1009676. [PMID: 34319975 PMCID: PMC8351996 DOI: 10.1371/journal.pgen.1009676] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 08/09/2021] [Accepted: 06/22/2021] [Indexed: 11/18/2022] Open
Abstract
Evolutionary forces like Hill-Robertson interference and negative epistasis can lead to deleterious mutations being found on distinct haplotypes. However, the extent to which these forces depend on the selection and dominance coefficients of deleterious mutations and shape genome-wide patterns of linkage disequilibrium (LD) in natural populations with complex demographic histories has not been tested. In this study, we first used forward-in-time simulations to predict how negative selection impacts LD. Under models where deleterious mutations have additive effects on fitness, deleterious variants less than 10 kb apart tend to be carried on different haplotypes relative to pairs of synonymous SNPs. In contrast, for recessive mutations, there is no consistent ordering of how selection coefficients affect LD decay, due to the complex interplay of different evolutionary effects. We then examined empirical data of modern humans from the 1000 Genomes Project. LD between derived alleles at nonsynonymous SNPs is lower compared to pairs of derived synonymous variants, suggesting that nonsynonymous derived alleles tend to occur on different haplotypes more than synonymous variants. This result holds when controlling for potential confounding factors by matching SNPs for frequency in the sample (allele count), physical distance, magnitude of background selection, and genetic distance between pairs of variants. Lastly, we introduce a new statistic HR(j) which allows us to detect interference using unphased genotypes. Application of this approach to high-coverage human genome sequences confirms our finding that nonsynonymous derived alleles tend to be located on different haplotypes more often than are synonymous derived alleles. Our findings suggest that interference may play a pervasive role in shaping patterns of LD between deleterious variants in the human genome, and consequently influences genome-wide patterns of LD.
Collapse
Affiliation(s)
- Jesse A. Garcia
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, California, United States of America
| | - Kirk E. Lohmueller
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, California, United States of America
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California, United States of America
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| |
Collapse
|
44
|
Johri P, Charlesworth B, Howell EK, Lynch M, Jensen JD. Revisiting the Notion of Deleterious Sweeps. Genetics 2021; 219:6298596. [PMID: 34125884 PMCID: PMC9101445 DOI: 10.1093/genetics/iyab094] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 06/08/2021] [Indexed: 11/14/2022] Open
Abstract
It has previously been shown that, conditional on its fixation, the time to fixation of a semi-dominant deleterious autosomal mutation in a randomly mating population is the same as that of an advantageous mutation. This result implies that deleterious mutations could generate selective sweep-like effects. Although their fixation probabilities greatly differ, the much larger input of deleterious relative to beneficial mutations suggests that this phenomenon could be important. We here examine how the fixation of mildly deleterious mutations affects levels and patterns of polymorphism at linked sites - both in the presence and absence of interference amongst deleterious mutations - and how this class of sites may contribute to divergence between-populations and species. We find that, while deleterious fixations are unlikely to represent a significant proportion of outliers in polymorphism-based genomic scans within populations, minor shifts in the frequencies of deleterious mutations can influence the proportions of private variants and the value of FST after a recent population split. As sites subject to deleterious mutations are necessarily found in functional genomic regions, interpretations in terms of recurrent positive selection may require reconsideration.
Collapse
Affiliation(s)
- Parul Johri
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, United Kingdom
| | - Emma K Howell
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Michael Lynch
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States.,Center for Mechanisms of Evolution, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, United States
| | - Jeffrey D Jensen
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States
| |
Collapse
|
45
|
Huang X, Fortier AL, Coffman AJ, Struck TJ, Irby MN, James JE, León-Burguete JE, Ragsdale AP, Gutenkunst RN. Inferring genome-wide correlations of mutation fitness effects between populations. Mol Biol Evol 2021; 38:4588-4602. [PMID: 34043790 PMCID: PMC8476148 DOI: 10.1093/molbev/msab162] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The effect of a mutation on fitness may differ between populations depending on environmental and genetic context, but little is known about the factors that underlie such differences. To quantify genome-wide correlations in mutation fitness effects, we developed a novel concept called a joint distribution of fitness effects (DFE) between populations. We then proposed a new statistic w to measure the DFE correlation between populations. Using simulation, we showed that inferring the DFE correlation from the joint allele frequency spectrum is statistically precise and robust. Using population genomic data, we inferred DFE correlations of populations in humans, Drosophila melanogaster, and wild tomatoes. In these species, we found that the overall correlation of the joint DFE was inversely related to genetic differentiation. In humans and D. melanogaster, deleterious mutations had a lower DFE correlation than tolerated mutations, indicating a complex joint DFE. Altogether, the DFE correlation can be reliably inferred, and it offers extensive insight into the genetics of population divergence.
Collapse
|
46
|
Font-Porterias N, Caro-Consuegra R, Lucas-Sánchez M, Lopez M, Giménez A, Carballo-Mesa A, Bosch E, Calafell F, Quintana-Murci L, Comas D. The Counteracting Effects of Demography on Functional Genomic Variation: The Roma Paradigm. Mol Biol Evol 2021; 38:2804-2817. [PMID: 33713133 PMCID: PMC8233508 DOI: 10.1093/molbev/msab070] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Demographic history plays a major role in shaping the distribution of genomic variation. Yet the interaction between different demographic forces and their effects in the genomes is not fully resolved in human populations. Here, we focus on the Roma population, the largest transnational ethnic minority in Europe. They have a South Asian origin and their demographic history is characterized by recent dispersals, multiple founder events, and extensive gene flow from non-Roma groups. Through the analyses of new high-coverage whole exome sequences and genome-wide array data for 89 Iberian Roma individuals together with forward simulations, we show that founder effects have reduced their genetic diversity and proportion of rare variants, gene flow has counteracted the increase in mutational load, runs of homozygosity show ancestry-specific patterns of accumulation of deleterious homozygotes, and selection signals primarily derive from preadmixture adaptation in the Roma population sources. The present study shows how two demographic forces, bottlenecks and admixture, act in opposite directions and have long-term balancing effects on the Roma genomes. Understanding how demography and gene flow shape the genome of an admixed population provides an opportunity to elucidate how genomic variation is modeled in human populations.
Collapse
Affiliation(s)
- Neus Font-Porterias
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain
| | - Rocio Caro-Consuegra
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain
| | - Marcel Lucas-Sánchez
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain
| | - Marie Lopez
- Human Evolutionary Genetics Unit, Institut Pasteur, UMR2000, CNRS, Paris, France
| | - Aaron Giménez
- Facultat de Sociologia, Universitat Autònoma de Barcelona, Barcelona, Spain
| | | | - Elena Bosch
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain.,Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Reus, Spain
| | - Francesc Calafell
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain
| | - Lluís Quintana-Murci
- Human Evolutionary Genetics Unit, Institut Pasteur, UMR2000, CNRS, Paris, France.,Human Genomics and Evolution, Collège de France, Paris, France
| | - David Comas
- Departament de Ciències Experimentals i de la Salut, Institut de Biologia Evolutiva (UPF-CSIC), Universitat Pompeu Fabra, Barcelona, Spain
| |
Collapse
|
47
|
Teixeira JC, Huber CD. The inflated significance of neutral genetic diversity in conservation genetics. Proc Natl Acad Sci U S A 2021; 118:e2015096118. [PMID: 33608481 PMCID: PMC7958437 DOI: 10.1073/pnas.2015096118] [Citation(s) in RCA: 135] [Impact Index Per Article: 45.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The current rate of species extinction is rapidly approaching unprecedented highs, and life on Earth presently faces a sixth mass extinction event driven by anthropogenic activity, climate change, and ecological collapse. The field of conservation genetics aims at preserving species by using their levels of genetic diversity, usually measured as neutral genome-wide diversity, as a barometer for evaluating population health and extinction risk. A fundamental assumption is that higher levels of genetic diversity lead to an increase in fitness and long-term survival of a species. Here, we argue against the perceived importance of neutral genetic diversity for the conservation of wild populations and species. We demonstrate that no simple general relationship exists between neutral genetic diversity and the risk of species extinction. Instead, a better understanding of the properties of functional genetic diversity, demographic history, and ecological relationships is necessary for developing and implementing effective conservation genetic strategies.
Collapse
Affiliation(s)
- João C Teixeira
- School of Biological Sciences, The University of Adelaide, Adelaide, 5005 SA, Australia;
- Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, The University of Adelaide, Adelaide, 5005 SA, Australia
| | - Christian D Huber
- School of Biological Sciences, The University of Adelaide, Adelaide, 5005 SA, Australia;
| |
Collapse
|
48
|
Kyriazis CC, Wayne RK, Lohmueller KE. Strongly deleterious mutations are a primary determinant of extinction risk due to inbreeding depression. Evol Lett 2021; 5:33-47. [PMID: 33552534 PMCID: PMC7857301 DOI: 10.1002/evl3.209] [Citation(s) in RCA: 78] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 11/10/2020] [Accepted: 11/21/2020] [Indexed: 11/08/2022] Open
Abstract
Human-driven habitat fragmentation and loss have led to a proliferation of small and isolated plant and animal populations with high risk of extinction. One of the main threats to extinction in these populations is inbreeding depression, which is primarily caused by recessive deleterious mutations becoming homozygous due to inbreeding. The typical approach for managing these populations is to maintain high genetic diversity, increasingly by translocating individuals from large populations to initiate a "genetic rescue." However, the limitations of this approach have recently been highlighted by the demise of the gray wolf population on Isle Royale, which declined to the brink of extinction soon after the arrival of a migrant from the large mainland wolf population. Here, we use a novel population genetic simulation framework to investigate the role of genetic diversity, deleterious variation, and demographic history in mediating extinction risk due to inbreeding depression in small populations. We show that, under realistic models of dominance, large populations harbor high levels of recessive strongly deleterious variation due to these mutations being hidden from selection in the heterozygous state. As a result, when large populations contract, they experience a substantially elevated risk of extinction after these strongly deleterious mutations are exposed by inbreeding. Moreover, we demonstrate that, although genetic rescue is broadly effective as a means to reduce extinction risk, its effectiveness can be greatly increased by drawing migrants from small or moderate-sized source populations rather than large source populations due to smaller populations harboring lower levels of recessive strongly deleterious variation. Our findings challenge the traditional conservation paradigm that focuses on maximizing genetic diversity in small populations in favor of a view that emphasizes minimizing strongly deleterious variation. These insights have important implications for managing small and isolated populations in the increasingly fragmented landscape of the Anthropocene.
Collapse
Affiliation(s)
- Christopher C. Kyriazis
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaLos AngelesCalifornia90095
| | - Robert K. Wayne
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaLos AngelesCalifornia90095
| | - Kirk E. Lohmueller
- Department of Ecology and Evolutionary BiologyUniversity of CaliforniaLos AngelesCalifornia90095
- Interdepartmental Program in BioinformaticsUniversity of CaliforniaLos AngelesCalifornia90095
- Department of Human Genetics, David Geffen School of MedicineUniversity of CaliforniaLos AngelesCalifornia90095
| |
Collapse
|
49
|
Zhen Y, Huber CD, Davies RW, Lohmueller KE. Greater strength of selection and higher proportion of beneficial amino acid changing mutations in humans compared with mice and Drosophila melanogaster. Genome Res 2020; 31:110-120. [PMID: 33208456 PMCID: PMC7849390 DOI: 10.1101/gr.256636.119] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2019] [Accepted: 11/10/2020] [Indexed: 12/19/2022]
Abstract
Quantifying and comparing the amount of adaptive evolution among different species is key to understanding how evolution works. Previous studies have shown differences in adaptive evolution across species; however, their specific causes remain elusive. Here, we use improved modeling of weakly deleterious mutations and the demographic history of the outgroup species and ancestral population and estimate that at least 20% of nonsynonymous substitutions between humans and an outgroup species were fixed by positive selection. This estimate is much higher than previous estimates, which did not correct for the sizes of the outgroup species and ancestral population. Next, we jointly estimate the proportion and selection coefficient (p+ and s+, respectively) of newly arising beneficial nonsynonymous mutations in humans, mice, and Drosophila melanogaster by examining patterns of polymorphism and divergence. We develop a novel composite likelihood framework to test whether these parameters differ across species. Overall, we reject a model with the same p+ and s+ of beneficial mutations across species and estimate that humans have a higher p+s+ compared with that of D. melanogaster and mice. We show that this result cannot be caused by biased gene conversion or hypermutable CpG sites. We discuss possible biological explanations that could generate the observed differences in the amount of adaptive evolution across species.
Collapse
Affiliation(s)
- Ying Zhen
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA.,Zhejiang Provincial Laboratory of Life Sciences and Biomedicine, Key Laboratory of Structural Biology of Zhejiang Province, School of Life Sciences, Westlake University, Hangzhou, Zhejiang, 310024, China.,Institute of Biology, Westlake Institute for Advanced Study, Hangzhou, Zhejiang, 310024, China
| | - Christian D Huber
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA.,School of Biological Sciences, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Robert W Davies
- Program in Genetics and Genome Biology and The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, M5G 0A4, Canada.,Department of Statistics, University of Oxford, Oxford, OX1 3LB, United Kingdom
| | - Kirk E Lohmueller
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA.,Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
| |
Collapse
|
50
|
Kutschera VE, Poelstra JW, Botero-Castro F, Dussex N, Gemmell NJ, Hunt GR, Ritchie MG, Rutz C, Wiberg RAW, Wolf JBW. Purifying Selection in Corvids Is Less Efficient on Islands. Mol Biol Evol 2020; 37:469-474. [PMID: 31633794 PMCID: PMC6993847 DOI: 10.1093/molbev/msz233] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Theory predicts that deleterious mutations accumulate more readily in small populations. As a consequence, mutation load is expected to be elevated in species where life-history strategies and geographic or historical contingencies reduce the number of reproducing individuals. Yet, few studies have empirically tested this prediction using genome-wide data in a comparative framework. We collected whole-genome sequencing data for 147 individuals across seven crow species (Corvus spp.). For each species, we estimated the distribution of fitness effects of deleterious mutations and compared it with proxies of the effective population size Ne. Island species with comparatively smaller geographic range sizes had a significantly increased mutation load. These results support the view that small populations have an elevated risk of mutational meltdown, which may contribute to the higher extinction rates observed in island species.
Collapse
Affiliation(s)
- Verena E Kutschera
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.,Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | | | - Fidel Botero-Castro
- Division of Evolutionary Biology, Faculty of Biology, LMU Munich, Planegg-Martinsried, Germany
| | - Nicolas Dussex
- Department of Anatomy, University of Otago, Dunedin, New Zealand.,Department of Bioinformatics and Genetics, Swedish Museum of Natural History, Stockholm, Sweden
| | - Neil J Gemmell
- Department of Anatomy, University of Otago, Dunedin, New Zealand
| | | | - Michael G Ritchie
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, United Kingdom
| | - Christian Rutz
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, United Kingdom
| | - R Axel W Wiberg
- Centre for Biological Diversity, School of Biology, University of St Andrews, St Andrews, United Kingdom.,Department of Environmental Sciences, Evolutionary Biology, University of Basel, Basel, Switzerland
| | - Jochen B W Wolf
- Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.,Division of Evolutionary Biology, Faculty of Biology, LMU Munich, Planegg-Martinsried, Germany
| |
Collapse
|