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Charlesworth B. The fitness consequences of genetic divergence between polymorphic gene arrangements. Genetics 2024; 226:iyad218. [PMID: 38147527 PMCID: PMC11090464 DOI: 10.1093/genetics/iyad218] [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: 10/15/2023] [Revised: 12/15/2023] [Accepted: 12/20/2023] [Indexed: 12/28/2023] Open
Abstract
Inversions restrict recombination when heterozygous with standard arrangements, but often have few noticeable phenotypic effects. Nevertheless, there are several examples of inversions that can be maintained polymorphic by strong selection under laboratory conditions. A long-standing model for the source of such selection is divergence between arrangements with respect to recessive or partially recessive deleterious mutations, resulting in a selective advantage to heterokaryotypic individuals over homokaryotypes. This paper uses a combination of analytical and numerical methods to investigate this model, for the simple case of an autosomal inversion with multiple independent nucleotide sites subject to mildly deleterious mutations. A complete lack of recombination in heterokaryotypes is assumed, as well as constancy of the frequency of the inversion over space and time. It is shown that a significantly higher mutational load will develop for the less frequent arrangement. A selective advantage to heterokaryotypes is only expected when the two alternative arrangements are nearly equal in frequency, so that their mutational loads are very similar in size. The effects of some Drosophila pseudoobscura polymorphic inversions on fitness traits seem to be too large to be explained by this process, although it may contribute to some of the observed effects. Several population genomic statistics can provide evidence for signatures of a reduced efficacy of selection associated with the rarer of two arrangements, but there is currently little published data that are relevant to the theoretical predictions.
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Affiliation(s)
- Brian Charlesworth
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK
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2
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Berdan EL, Barton NH, Butlin R, Charlesworth B, Faria R, Fragata I, Gilbert KJ, Jay P, Kapun M, Lotterhos KE, Mérot C, Durmaz Mitchell E, Pascual M, Peichel CL, Rafajlović M, Westram AM, Schaeffer SW, Johannesson K, Flatt T. How chromosomal inversions reorient the evolutionary process. J Evol Biol 2023; 36:1761-1782. [PMID: 37942504 DOI: 10.1111/jeb.14242] [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: 05/05/2023] [Revised: 09/13/2023] [Accepted: 10/05/2023] [Indexed: 11/10/2023]
Abstract
Inversions are structural mutations that reverse the sequence of a chromosome segment and reduce the effective rate of recombination in the heterozygous state. They play a major role in adaptation, as well as in other evolutionary processes such as speciation. Although inversions have been studied since the 1920s, they remain difficult to investigate because the reduced recombination conferred by them strengthens the effects of drift and hitchhiking, which in turn can obscure signatures of selection. Nonetheless, numerous inversions have been found to be under selection. Given recent advances in population genetic theory and empirical study, here we review how different mechanisms of selection affect the evolution of inversions. A key difference between inversions and other mutations, such as single nucleotide variants, is that the fitness of an inversion may be affected by a larger number of frequently interacting processes. This considerably complicates the analysis of the causes underlying the evolution of inversions. We discuss the extent to which these mechanisms can be disentangled, and by which approach.
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Affiliation(s)
- Emma L Berdan
- Bioinformatics Core, Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, USA
- Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Nicholas H Barton
- Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria
| | - Roger Butlin
- Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
- Ecology and Evolutionary Biology, School of Bioscience, The University of Sheffield, Sheffield, UK
| | - Brian Charlesworth
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
| | - Rui Faria
- CIBIO-InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal
- BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO, Vairão, Portugal
| | - Inês Fragata
- CHANGE - Global Change and Sustainability Institute/Animal Biology Department, cE3c - Center for Ecology, Evolution and Environmental Changes, Faculty of Sciences, University of Lisbon, Lisbon, Portugal
| | | | - Paul Jay
- Center for GeoGenetics, University of Copenhagen, Copenhagen, Denmark
| | - Martin Kapun
- Center for Anatomy and Cell Biology, Medical University of Vienna, Vienna, Austria
- Central Research Laboratories, Natural History Museum of Vienna, Vienna, Austria
| | - Katie E Lotterhos
- Department of Marine and Environmental Sciences, Northeastern University, Boston, Massachusetts, USA
| | - Claire Mérot
- UMR 6553 Ecobio, Université de Rennes, OSUR, CNRS, Rennes, France
| | - Esra Durmaz Mitchell
- Department of Biology, University of Fribourg, Fribourg, Switzerland
- Functional Genomics & Metabolism Research Unit, Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
| | - Marta Pascual
- Departament de Genètica, Microbiologia i Estadística, Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Barcelona, Spain
| | - Catherine L Peichel
- Division of Evolutionary Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
| | - Marina Rafajlović
- Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
- Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden
| | - Anja M Westram
- Institute of Science and Technology Austria (ISTA), Klosterneuburg, Austria
- Faculty of Biosciences and Aquaculture, Nord University, Bodø, Norway
| | - Stephen W Schaeffer
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania, USA
| | - Kerstin Johannesson
- Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden
- Tjärnö Marine Laboratory, Department of Marine Sciences, University of Gothenburg, Strömstad, Sweden
| | - Thomas Flatt
- Department of Biology, University of Fribourg, Fribourg, Switzerland
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3
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Soto TY, Rojas-Gutierrez JD, Oakley CG. Can heterosis and inbreeding depression explain the maintenance of outcrossing in a cleistogamous perennial? AMERICAN JOURNAL OF BOTANY 2023; 110:e16240. [PMID: 37672596 DOI: 10.1002/ajb2.16240] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 08/17/2023] [Accepted: 08/18/2023] [Indexed: 09/08/2023]
Abstract
PREMISE What maintains mixed mating is an evolutionary enigma. Cleistogamy-the production of both potentially outcrossing chasmogamous and obligately selfing cleistogamous flowers on the same individual plant-is an excellent system to study the costs of selfing. Inbreeding depression can prevent the evolution of greater selfing within populations, and heterosis in crosses between populations may further tip the balance in favor of outcrossing. Few empirical estimates of inbreeding depression and heterosis in the same system exist for cleistogamous species. METHODS We investigate the potential costs of selfing by quantifying inbreeding depression and heterosis in three populations of the cleistogamous perennial Ruellia humilis Nutt (Acanthaceae). We performed three types of hand-pollinations-self, outcross-within, and outcross-between populations-and measured seed number, germination, total flower production, and estimated cumulative fitness for the resulting progeny in a greenhouse experiment. RESULTS We found moderate inbreeding depression for cumulative fitness (<30%) in two populations, but outbreeding depression for crosses within a third population (-26%). For between-population crosses, there was weak to modest heterosis (11-47%) in two of the population combinations, but modest to strong outbreeding depression (-21 to -71%) in the other four combinations. CONCLUSIONS Neither inbreeding depression nor heterosis was of sufficient magnitude to explain the continued production of chasmogamous flowers given the relative energetic advantage of cleistogamous flowers previously estimated for these populations. Outbreeding depression either within or between populations makes the maintenance of chasmogamous flowers even harder to explain. More information is needed on the genetic basis of cleistogamy to resolve this conundrum.
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Affiliation(s)
- Tatyana Y Soto
- Department of Botany and Plant Pathology and the Center for Plant Biology, Purdue University, West Lafayette, IN, USA
| | - Juan Diego Rojas-Gutierrez
- Department of Botany and Plant Pathology and the Center for Plant Biology, Purdue University, West Lafayette, IN, USA
| | - Christopher G Oakley
- Department of Botany and Plant Pathology and the Center for Plant Biology, Purdue University, West Lafayette, IN, USA
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Kapun M, Mitchell ED, Kawecki TJ, Schmidt P, Flatt T. An Ancestral Balanced Inversion Polymorphism Confers Global Adaptation. Mol Biol Evol 2023; 40:msad118. [PMID: 37220650 PMCID: PMC10234209 DOI: 10.1093/molbev/msad118] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 04/17/2023] [Accepted: 05/19/2023] [Indexed: 05/25/2023] Open
Abstract
Since the pioneering work of Dobzhansky in the 1930s and 1940s, many chromosomal inversions have been identified, but how they contribute to adaptation remains poorly understood. In Drosophila melanogaster, the widespread inversion polymorphism In(3R)Payne underpins latitudinal clines in fitness traits on multiple continents. Here, we use single-individual whole-genome sequencing, transcriptomics, and published sequencing data to study the population genomics of this inversion on four continents: in its ancestral African range and in derived populations in Europe, North America, and Australia. Our results confirm that this inversion originated in sub-Saharan Africa and subsequently became cosmopolitan; we observe marked monophyletic divergence of inverted and noninverted karyotypes, with some substructure among inverted chromosomes between continents. Despite divergent evolution of this inversion since its out-of-Africa migration, derived non-African populations exhibit similar patterns of long-range linkage disequilibrium between the inversion breakpoints and major peaks of divergence in its center, consistent with balancing selection and suggesting that the inversion harbors alleles that are maintained by selection on several continents. Using RNA-sequencing, we identify overlap between inversion-linked single-nucleotide polymorphisms and loci that are differentially expressed between inverted and noninverted chromosomes. Expression levels are higher for inverted chromosomes at low temperature, suggesting loss of buffering or compensatory plasticity and consistent with higher inversion frequency in warm climates. Our results suggest that this ancestrally tropical balanced polymorphism spread around the world and became latitudinally assorted along similar but independent climatic gradients, always being frequent in subtropical/tropical areas but rare or absent in temperate climates.
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Affiliation(s)
- Martin Kapun
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
- Department of Biology, University of Fribourg, Fribourg, Switzerland
- Division of Cell and Developmental Biology, Medical University of Vienna, Vienna, Austria
- Natural History Museum Vienna, Zentrale Forschungslaboratorien, Vienna, Austria
| | - Esra Durmaz Mitchell
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
- Department of Biology, University of Fribourg, Fribourg, Switzerland
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Tadeusz J Kawecki
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Paul Schmidt
- Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Thomas Flatt
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
- Department of Biology, University of Fribourg, Fribourg, Switzerland
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De Kort H, Legrand S, Honnay O, Buckley J. Transposable elements maintain genome-wide heterozygosity in inbred populations. Nat Commun 2022; 13:7022. [PMID: 36396660 PMCID: PMC9672359 DOI: 10.1038/s41467-022-34795-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Accepted: 11/08/2022] [Indexed: 11/18/2022] Open
Abstract
Elevated levels of inbreeding increase the risk of inbreeding depression and extinction, yet many inbred species are widespread, suggesting that inbreeding has little impact on evolutionary potential. Here, we explore the potential for transposable elements (TEs) to maintain genetic variation in functional genomic regions under extreme inbreeding. Capitalizing on the mixed mating system of Arabidopsis lyrata, we assess genome-wide heterozygosity and signatures of selection at single nucleotide polymorphisms near transposable elements across an inbreeding gradient. Under intense inbreeding, we find systematically elevated heterozygosity downstream of several TE superfamilies, associated with signatures of balancing selection. In addition, we demonstrate increased heterozygosity in stress-responsive genes that consistently occur downstream of TEs. We finally reveal that TE superfamilies are associated with specific signatures of selection that are reproducible across independent evolutionary lineages of A. lyrata. Together, our study provides an important hypothesis for the success of self-fertilizing species.
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Affiliation(s)
- Hanne De Kort
- grid.5596.f0000 0001 0668 7884Plant Conservation and Population Biology, University of Leuven, Kasteelpark Arenberg 31-2435, BE-3001 Leuven, Belgium
| | - Sylvain Legrand
- grid.503422.20000 0001 2242 6780Univ. Lille, CNRS, UMR 8198 - Evo-Eco-Paleo, F-59000 Lille, France
| | - Olivier Honnay
- grid.5596.f0000 0001 0668 7884Plant Conservation and Population Biology, University of Leuven, Kasteelpark Arenberg 31-2435, BE-3001 Leuven, Belgium
| | - James Buckley
- grid.11201.330000 0001 2219 0747School of Biological and Marine Sciences, University of Plymouth, Plymouth, PL1 2BT UK
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Sandner TM, Gemeinholzer B, Lemmer J, Matthies D, Ensslin A. Continuous inbreeding affects genetic variation, phenology, and reproductive strategy in ex situ cultivated Digitalis lutea. AMERICAN JOURNAL OF BOTANY 2022; 109:1545-1559. [PMID: 36164840 DOI: 10.1002/ajb2.16075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 08/31/2022] [Accepted: 08/31/2022] [Indexed: 06/16/2023]
Abstract
PREMISE Ex situ cultivation is important for plant conservation, but cultivation in small populations may result in genetic changes by drift, inbreeding, or unconscious selection. Repeated inbreeding potentially influences not only plant fitness, but also floral traits and interactions with pollinators, which has not yet been studied in an ex situ context. METHODS We studied the molecular genetic variation of Digitalis lutea from a botanic garden population cultivated for 30 years, a frozen seed bank conserving the original genetic structure, and two current wild populations including the source population. In a common garden, we studied the effects of experimental inbreeding and between-population crosses on performance, reproductive traits, and flower visitation of plants from the garden and a wild population. RESULTS Significant genetic differentiation was found between the garden population and the wild population from which the seeds had originally been gathered. After experimental selfing, inbreeding depression was only found for germination and leaf size of plants from the wild population, indicating a history of inbreeding in the smaller garden population. Moreover, garden plants flowered earlier and had floral traits related to selfing, whereas wild plants had traits related to attracting pollinators. Bumblebees visited more flowers of outbred than inbred plants and of wild than garden plants. CONCLUSIONS Our case study suggests that high levels of inbreeding during ex situ cultivation can influence reproductive traits and thus interactions with pollinators. Together with the effects of genetic erosion and unconscious selection, these changes may affect the success of reintroductions into natural habitats.
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Affiliation(s)
- Tobias M Sandner
- Plant Ecology, Department of Biology, Philipps-Universität Marburg, Marburg, Germany
| | | | | | - Diethart Matthies
- Plant Ecology, Department of Biology, Philipps-Universität Marburg, Marburg, Germany
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7
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Whiteford S, van’t Hof AE, Krishna R, Marubbi T, Widdison S, Saccheri IJ, Guest M, Morrison NI, Darby AC. Recovering individual haplotypes and a contiguous genome assembly from pooled long-read sequencing of the diamondback moth (Lepidoptera: Plutellidae). G3 (BETHESDA, MD.) 2022; 12:jkac210. [PMID: 35980174 PMCID: PMC9526047 DOI: 10.1093/g3journal/jkac210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 07/25/2022] [Indexed: 06/15/2023]
Abstract
The assembly of divergent haplotypes using noisy long-read data presents a challenge to the reconstruction of haploid genome assemblies, due to overlapping distributions of technical sequencing error, intralocus genetic variation, and interlocus similarity within these data. Here, we present a comparative analysis of assembly algorithms representing overlap-layout-consensus, repeat graph, and de Bruijn graph methods. We examine how postprocessing strategies attempting to reduce redundant heterozygosity interact with the choice of initial assembly algorithm and ultimately produce a series of chromosome-level assemblies for an agricultural pest, the diamondback moth, Plutella xylostella (L.). We compare evaluation methods and show that BUSCO analyses may overestimate haplotig removal processing in long-read draft genomes, in comparison to a k-mer method. We discuss the trade-offs inherent in assembly algorithm and curation choices and suggest that "best practice" is research question dependent. We demonstrate a link between allelic divergence and allele-derived contig redundancy in final genome assemblies and document the patterns of coding and noncoding diversity between redundant sequences. We also document a link between an excess of nonsynonymous polymorphism and haplotigs that are unresolved by assembly or postassembly algorithms. Finally, we discuss how this phenomenon may have relevance for the usage of noisy long-read genome assemblies in comparative genomics.
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Affiliation(s)
- Samuel Whiteford
- Corresponding author: Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK.
| | - Arjen E van’t Hof
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Ritesh Krishna
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
- IBM Research UK, STFC Daresbury Laboratory, Warrington WA4 4AD, UK
| | | | - Stephanie Widdison
- General Bioinformatics, Jealott's Hill International Research Centre, Bracknell RG42 6EY, UK
| | - Ilik J Saccheri
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
| | - Marcus Guest
- Syngenta, Jealott's Hill International Research Centre, Bracknell, RG42 6EY, UK
| | | | - Alistair C Darby
- Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK
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Achakkagari SR, Kyriakidou M, Gardner KM, De Koeyer D, De Jong H, Strömvik MV, Tai HH. Genome sequencing of adapted diploid potato clones. FRONTIERS IN PLANT SCIENCE 2022; 13:954933. [PMID: 36003817 PMCID: PMC9394749 DOI: 10.3389/fpls.2022.954933] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Cultivated potato is a vegetatively propagated crop, and most varieties are autotetraploid with high levels of heterozygosity. Reducing the ploidy and breeding potato at the diploid level can increase efficiency for genetic improvement including greater ease of introgression of diploid wild relatives and more efficient use of genomics and markers in selection. More recently, selfing of diploids for generation of inbred lines for F1 hybrid breeding has had a lot of attention in potato. The current study provides genomics resources for nine legacy non-inbred adapted diploid potato clones developed at Agriculture and Agri-Food Canada. De novo genome sequence assembly using 10× Genomics and Illumina sequencing technologies show the genome sizes ranged from 712 to 948 Mbp. Structural variation was identified by comparison to two references, the potato DMv6.1 genome and the phased RHv3 genome, and a k-mer based analysis of sequence reads showed the genome heterozygosity range of 1 to 9.04% between clones. A genome-wide approach was taken to scan 5 Mb bins to visualize patterns of heterozygous deleterious alleles. These were found dispersed throughout the genome including regions overlapping segregation distortions. Novel variants of the StCDF1 gene conferring earliness of tuberization were found among these clones, which all produce tubers under long days. The genomes will be useful tools for genome design for potato breeding.
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Affiliation(s)
| | - Maria Kyriakidou
- Department of Plant Science, McGill University, Sainte-Anne-de-Bellevue, QC, Canada
| | - Kyle M. Gardner
- Fredericton Research and Development Centre, Agriculture and Agri-Food Canada, Fredericton, NB, Canada
| | - David De Koeyer
- Fredericton Research and Development Centre, Agriculture and Agri-Food Canada, Fredericton, NB, Canada
| | - Hielke De Jong
- Fredericton Research and Development Centre, Agriculture and Agri-Food Canada, Fredericton, NB, Canada
| | - Martina V. Strömvik
- Department of Plant Science, McGill University, Sainte-Anne-de-Bellevue, QC, Canada
| | - Helen H. Tai
- Fredericton Research and Development Centre, Agriculture and Agri-Food Canada, Fredericton, NB, Canada
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9
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Stetsenko R, Roze D. The evolution of recombination in self-fertilizing organisms. Genetics 2022; 222:6656355. [PMID: 35929790 PMCID: PMC9434187 DOI: 10.1093/genetics/iyac114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Cytological data from flowering plants suggest that the evolution of recombination rates is affected by the mating system of organisms, as higher chiasma frequencies are often observed in self-fertilizing species compared with their outcrossing relatives. Understanding the evolutionary cause of this effect is of particular interest, as it may shed light on the selective forces favoring recombination in natural populations. While previous models showed that inbreeding may have important effects on selection for recombination, existing analytical treatments are restricted to the case of loosely linked loci and weak selfing rates, and ignore the stochastic effect of genetic interference (Hill-Robertson effect), known to be an important component of selection for recombination in randomly mating populations. In this article, we derive general expressions quantifying the stochastic and deterministic components of selection acting on a mutation affecting the genetic map length of a whole chromosome along which deleterious mutations occur, valid for arbitrary selfing rates. The results show that selfing generally increases selection for recombination caused by interference among mutations as long as selection against deleterious alleles is sufficiently weak. While interference is often the main driver of selection for recombination under tight linkage or high selfing rates, deterministic effects can play a stronger role under intermediate selfing rates and high recombination, selecting against recombination in the absence of epistasis, but favoring recombination when epistasis is negative. Individual-based simulation results indicate that our analytical model often provides accurate predictions for the strength of selection on recombination under partial selfing.
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Affiliation(s)
- Roman Stetsenko
- CNRS, IRL 3614 Evolutionary Biology and Ecology of Algae, 29688 Roscoff, France.,Sorbonne Université, Station Biologique de Roscoff, 29688 Roscoff, France
| | - Denis Roze
- CNRS, IRL 3614 Evolutionary Biology and Ecology of Algae, 29688 Roscoff, France.,Sorbonne Université, Station Biologique de Roscoff, 29688 Roscoff, France
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10
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Pérez‐Pereira N, López‐Cortegano E, García‐Dorado A, Caballero A. Prediction of fitness under different breeding designs in conservation programs. Anim Conserv 2022. [DOI: 10.1111/acv.12804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- N. Pérez‐Pereira
- Centro de Investigación Mariña Universidade de Vigo, Facultade de Bioloxía Vigo Spain
| | - E. López‐Cortegano
- Centro de Investigación Mariña Universidade de Vigo, Facultade de Bioloxía Vigo Spain
| | - A. García‐Dorado
- Departamento de Genética, Facultad de Ciencias Biológicas Universidad Complutense Madrid Spain
| | - A. Caballero
- Centro de Investigación Mariña Universidade de Vigo, Facultade de Bioloxía Vigo Spain
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11
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Charlesworth B. The effects of weak selection on neutral diversity at linked sites. Genetics 2022; 221:6527636. [PMID: 35150278 PMCID: PMC9071562 DOI: 10.1093/genetics/iyac027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 02/04/2022] [Indexed: 11/15/2022] Open
Abstract
The effects of selection on variability at linked sites have an important influence on levels and patterns of within-population variation across the genome. Most theoretical models of these effects have assumed that selection is sufficiently strong that allele frequency changes at the loci concerned are largely deterministic. These models have led to the conclusion that directional selection for selectively favorable mutations, or against recurrent deleterious mutations, reduces nucleotide site diversity at linked neutral sites. Recent work has shown, however, that fixations of weakly selected mutations, accompanied by significant stochastic changes in allele frequencies, can sometimes cause higher diversity at linked sites when compared with the effects of fixations of neutral mutations. This study extends this work by deriving approximate expressions for the mean conditional times to fixation and loss of mutations subject to selection, and analyzing the conditions under which selection increases rather than reduces these times. Simulations are used to examine the relations between diversity at a neutral site and the fixation and loss times of mutations at a linked site that is subject to selection. It is shown that the long-term level of neutral diversity can be increased over the purely neutral value by recurrent fixations and losses of linked, weakly selected dominant or partially dominant favorable mutations, or linked recessive or partially recessive deleterious mutations. The results are used to examine the conditions under which associative overdominance, as opposed to background selection, is likely to operate.
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Affiliation(s)
- Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, United Kingdom
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12
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Adams PE, Crist AB, Young EM, Willis JH, Phillips PC, Fierst JL. Slow Recovery from Inbreeding Depression Generated by the Complex Genetic Architecture of Segregating Deleterious Mutations. Mol Biol Evol 2022; 39:msab330. [PMID: 34791426 PMCID: PMC8789292 DOI: 10.1093/molbev/msab330] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The deleterious effects of inbreeding have been of extreme importance to evolutionary biology, but it has been difficult to characterize the complex interactions between genetic constraints and selection that lead to fitness loss and recovery after inbreeding. Haploid organisms and selfing organisms like the nematode Caenorhabditis elegans are capable of rapid recovery from the fixation of novel deleterious mutation; however, the potential for recovery and genomic consequences of inbreeding in diploid, outcrossing organisms are not well understood. We sought to answer two questions: 1) Can a diploid, outcrossing population recover from inbreeding via standing genetic variation and new mutation? and 2) How does allelic diversity change during recovery? We inbred C. remanei, an outcrossing relative of C. elegans, through brother-sister mating for 30 generations followed by recovery at large population size. Inbreeding reduced fitness but, surprisingly, recovery from inbreeding at large populations sizes generated only very moderate fitness recovery after 300 generations. We found that 65% of ancestral single nucleotide polymorphisms (SNPs) were fixed in the inbred population, far fewer than the theoretical expectation of ∼99%. Under recovery, 36 SNPs across 30 genes involved in alimentary, muscular, nervous, and reproductive systems changed reproducibly across replicates, indicating that strong selection for fitness recovery does exist. Our results indicate that recovery from inbreeding depression via standing genetic variation and mutation is likely to be constrained by the large number of segregating deleterious variants present in natural populations, limiting the capacity for recovery of small populations.
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Affiliation(s)
- Paula E Adams
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
| | - Anna B Crist
- Department of Genomes and Genetics, Institut Pasteur, Paris, France
| | - Ellen M Young
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - John H Willis
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - Patrick C Phillips
- Institute of Ecology and Evolution, University of Oregon, Eugene, OR, USA
| | - Janna L Fierst
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
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Abstract
AbstractGenetic rescue is increasingly considered a promising and underused conservation strategy to reduce inbreeding depression and restore genetic diversity in endangered populations, but the empirical evidence supporting its application is limited to a few generations. Here we discuss on the light of theory the role of inbreeding depression arising from partially recessive deleterious mutations and of genetic purging as main determinants of the medium to long-term success of rescue programs. This role depends on two main predictions: (1) The inbreeding load hidden in populations with a long stable demography increases with the effective population size; and (2) After a population shrinks, purging tends to remove its (partially) recessive deleterious alleles, a process that is slower but more efficient for large populations than for small ones. We also carry out computer simulations to investigate the impact of genetic purging on the medium to long term success of genetic rescue programs. For some scenarios, it is found that hybrid vigor followed by purging will lead to sustained successful rescue. However, there may be specific situations where the recipient population is so small that it cannot purge the inbreeding load introduced by migrants, which would lead to increased fitness inbreeding depression and extinction risk in the medium to long term. In such cases, the risk is expected to be higher if migrants came from a large non-purged population with high inbreeding load, particularly after the accumulation of the stochastic effects ascribed to repeated occasional migration events. Therefore, under the specific deleterious recessive mutation model considered, we conclude that additional caution should be taken in rescue programs. Unless the endangered population harbors some distinctive genetic singularity whose conservation is a main concern, restoration by continuous stable gene flow should be considered, whenever feasible, as it reduces the extinction risk compared to repeated occasional migration and can also allow recolonization events.
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