1
|
Wang Y, Duchen P, Chávez A, Sree KS, Appenroth KJ, Zhao H, Höfer M, Huber M, Xu S. Population genomics and epigenomics of Spirodela polyrhiza provide insights into the evolution of facultative asexuality. Commun Biol 2024; 7:581. [PMID: 38755313 PMCID: PMC11099151 DOI: 10.1038/s42003-024-06266-7] [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: 08/01/2023] [Accepted: 04/30/2024] [Indexed: 05/18/2024] Open
Abstract
Many plants are facultatively asexual, balancing short-term benefits with long-term costs of asexuality. During range expansion, natural selection likely influences the genetic controls of asexuality in these organisms. However, evidence of natural selection driving asexuality is limited, and the evolutionary consequences of asexuality on the genomic and epigenomic diversity remain controversial. We analyzed population genomes and epigenomes of Spirodela polyrhiza, (L.) Schleid., a facultatively asexual plant that flowers rarely, revealing remarkably low genomic diversity and DNA methylation levels. Within species, demographic history and the frequency of asexual reproduction jointly determined intra-specific variations of genomic diversity and DNA methylation levels. Genome-wide scans revealed that genes associated with stress adaptations, flowering and embryogenesis were under positive selection. These data are consistent with the hypothesize that natural selection can shape the evolution of asexuality during habitat expansions, which alters genomic and epigenomic diversity levels.
Collapse
Affiliation(s)
- Yangzi Wang
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany
- Institute for Evolution and Biodiversity, University of Münster, 48161, Münster, Germany
| | - Pablo Duchen
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany
- Institute for Evolution and Biodiversity, University of Münster, 48161, Münster, Germany
| | - Alexandra Chávez
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany
- Institute for Evolution and Biodiversity, University of Münster, 48161, Münster, Germany
- Institute of Plant Biology and Biotechnology, University of Münster, 48161, Münster, Germany
| | - K Sowjanya Sree
- Department of Environmental Science, Central University of Kerala, Periya, 671320, India
| | - Klaus J Appenroth
- Matthias Schleiden Institute - Plant Physiology, Friedrich Schiller University of Jena, 07743, Jena, Germany
| | - Hai Zhao
- Chengdu Institute of Biology, Chinese Academy of Sciences, 6100641, Chengdu, China
| | - Martin Höfer
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany
- Institute for Evolution and Biodiversity, University of Münster, 48161, Münster, Germany
| | - Meret Huber
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany
- Institute of Plant Biology and Biotechnology, University of Münster, 48161, Münster, Germany
| | - Shuqing Xu
- Institute of Organismic and Molecular Evolution, University of Mainz, 55128, Mainz, Germany.
- Institute for Evolution and Biodiversity, University of Münster, 48161, Münster, Germany.
- Institute for Quantitative and Computational Biosciences, University of Mainz, 55218, Mainz, Germany.
| |
Collapse
|
2
|
Cole R, Holroyd N, Tracey A, Berriman M, Viney M. The parasitic nematode Strongyloides ratti exists predominantly as populations of long-lived asexual lineages. Nat Commun 2023; 14:6427. [PMID: 37833369 PMCID: PMC10575991 DOI: 10.1038/s41467-023-42250-1] [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: 02/21/2022] [Accepted: 10/05/2023] [Indexed: 10/15/2023] Open
Abstract
Nematodes are important parasites of people and animals, and in natural ecosystems they are a major ecological force. Strongyloides ratti is a common parasitic nematode of wild rats and we have investigated its population genetics using single-worm, whole-genome sequencing. We find that S. ratti populations in the UK consist of mixtures of mainly asexual lineages that are widely dispersed across a host population. These parasite lineages are likely very old and may have originated in Asia from where rats originated. Genes that underly the parasitic phase of the parasite's life cycle are hyperdiverse compared with the rest of the genome, and this may allow the parasites to maximise their fitness in a diverse host population. These patterns of parasitic nematode population genetics have not been found before and may also apply to Strongyloides spp. that infect people, which will affect how we should approach their control.
Collapse
Affiliation(s)
- Rebecca Cole
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, UK
| | - Nancy Holroyd
- Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK
| | - Alan Tracey
- Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK
| | - Matt Berriman
- Wellcome Sanger Institute, Wellcome Genome Campus, Hinxton, CB10 1SA, UK
- School of Infection & Immunity, University of Glasgow, 120 University Place, Glasgow, G12 8TA, UK
| | - Mark Viney
- School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, UK.
- Department of Evolution, Ecology and Behaviour, University of Liverpool, Liverpool, L69 7ZB, UK.
| |
Collapse
|
3
|
Teterina AA, Willis JH, Lukac M, Jovelin R, Cutter AD, Phillips PC. Genomic diversity landscapes in outcrossing and selfing Caenorhabditis nematodes. PLoS Genet 2023; 19:e1010879. [PMID: 37585484 PMCID: PMC10461856 DOI: 10.1371/journal.pgen.1010879] [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: 12/28/2022] [Revised: 08/28/2023] [Accepted: 07/21/2023] [Indexed: 08/18/2023] Open
Abstract
Caenorhabditis nematodes form an excellent model for studying how the mode of reproduction affects genetic diversity, as some species reproduce via outcrossing whereas others can self-fertilize. Currently, chromosome-level patterns of diversity and recombination are only available for self-reproducing Caenorhabditis, making the generality of genomic patterns across the genus unclear given the profound potential influence of reproductive mode. Here we present a whole-genome diversity landscape, coupled with a new genetic map, for the outcrossing nematode C. remanei. We demonstrate that the genomic distribution of recombination in C. remanei, like the model nematode C. elegans, shows high recombination rates on chromosome arms and low rates toward the central regions. Patterns of genetic variation across the genome are also similar between these species, but differ dramatically in scale, being tenfold greater for C. remanei. Historical reconstructions of variation in effective population size over the past million generations echo this difference in polymorphism. Evolutionary simulations demonstrate how selection, recombination, mutation, and selfing shape variation along the genome, and that multiple drivers can produce patterns similar to those observed in natural populations. The results illustrate how genome organization and selection play a crucial role in shaping the genomic pattern of diversity whereas demographic processes scale the level of diversity across the genome as a whole.
Collapse
Affiliation(s)
- Anastasia A. Teterina
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon, United States of America
- Center of Parasitology, Severtsov Institute of Ecology and Evolution RAS, Moscow, Russia
| | - John H. Willis
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon, United States of America
| | - Matt Lukac
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon, United States of America
| | - Richard Jovelin
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Asher D. Cutter
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Patrick C. Phillips
- Institute of Ecology and Evolution, University of Oregon, Eugene, Oregon, United States of America
| |
Collapse
|
4
|
Henshaw JM, Bittlingmaier M, Schärer L. Hermaphroditic origins of anisogamy. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220283. [PMID: 36934747 PMCID: PMC10024982 DOI: 10.1098/rstb.2022.0283] [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: 09/01/2022] [Accepted: 11/23/2022] [Indexed: 03/21/2023] Open
Abstract
Anisogamy-the size dimorphism of gametes-is the defining difference between the male and female sexual strategies. Game-theoretic thinking led to the first convincing explanation for the evolutionary origins of anisogamy in the 1970s. Since then, formal game-theoretic models have continued to refine our understanding of when and why anisogamy should evolve. Such models typically presume that the earliest anisogamous organisms had separate sexes. However, in most taxa, there is no empirical evidence to support this assumption. Here, we present a model of the coevolution of gamete size and sex allocation, which allows for anisogamy to emerge alongside either hermaphroditism or separate sexes. We show that hermaphroditic anisogamy can evolve directly from isogamous ancestors when the average size of spawning groups is small and fertilization is relatively efficient. Sex allocation under hermaphroditism becomes increasingly female-biased as group size decreases and the degree of anisogamy increases. When spawning groups are very small, our model also predicts the existence of complex isogamous organisms in which individuals allocate resources equally to two large gamete types. We discuss common, but potentially unwarranted, assumptions in the literature that could be relaxed in future models. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.
Collapse
Affiliation(s)
- Jonathan M. Henshaw
- Institute of Biology I, University of Freiburg, Hauptstraße 1, D-79104 Freiburg, Germany
| | - Markus Bittlingmaier
- Institute of Biology I, University of Freiburg, Hauptstraße 1, D-79104 Freiburg, Germany
- Theoretical and Experimental Ecology Station, CNRS, 2 route du CNRS, 09200 Moulis, France
| | - Lukas Schärer
- Zoological Institute, Department of Environmental Sciences, University of Basel, Basel CH-4051, Switzerland
| |
Collapse
|
5
|
Conflicting effects of recombination on the evolvability and robustness in neutrally evolving populations. PLoS Comput Biol 2022; 18:e1010710. [DOI: 10.1371/journal.pcbi.1010710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 12/05/2022] [Accepted: 11/04/2022] [Indexed: 11/22/2022] Open
Abstract
Understanding the benefits and costs of recombination under different scenarios of evolutionary adaptation remains an open problem for theoretical and experimental research. In this study, we focus on finite populations evolving on neutral networks comprising viable and unfit genotypes. We provide a comprehensive overview of the effects of recombination by jointly considering different measures of evolvability and mutational robustness over a broad parameter range, such that many evolutionary regimes are covered. We find that several of these measures vary non-monotonically with the rates of mutation and recombination. Moreover, the presence of unfit genotypes that introduce inhomogeneities in the network of viable states qualitatively alters the effects of recombination. We conclude that conflicting trends induced by recombination can be explained by an emerging trade-off between evolvability on the one hand, and mutational robustness on the other. Finally, we discuss how different implementations of the recombination scheme in theoretical models can affect the observed dependence on recombination rate through a coupling between recombination and genetic drift.
Collapse
|
6
|
da Cunha NL, Xue H, Wright SI, Barrett SCH. Genetic variation and clonal diversity in floating aquatic plants: Comparative genomic analysis of water hyacinth species in their native range. Mol Ecol 2022; 31:5307-5325. [PMID: 35984729 DOI: 10.1111/mec.16664] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 07/24/2022] [Accepted: 08/10/2022] [Indexed: 12/15/2022]
Abstract
Many eukaryotic organisms reproduce by sexual and asexual reproduction. Genetic diversity in populations can be strongly dependent on the relative importance of these two reproductive modes. Here, we compare the amounts and patterns of genetic diversity in related water hyacinths that differ in their propensity for clonal propagation - highly clonal Eichhornia crassipes and moderately clonal E. azurea (Pontederiaceae). Our comparisons involved genotype-by-sequencing (GBS) of 137 E. crassipes ramets from 60 locations (193,495 nucleotide sites) and 118 E. azurea ramets from 53 locations (198,343 nucleotide sites) among six hydrological basins in central South America, the native range of both species. We predicted that because of more prolific clonal propagation, E. crassipes would exhibit lower clonal diversity than E. azurea. This prediction was supported by all measures of clonal diversity that we examined. Eichhornia crassipes also had a larger excess of heterozygotes at variant sites, another signature of clonality. However, genome-wide heterozygosity was not significantly different between the species. Eichhornia crassipes had weaker spatial genetic structure and lower levels of differentiation among hydrological basins than E. azurea, probably because of higher clonality and more extensive dispersal of its free-floating life form. Our findings for E. crassipes contrast with earlier studies from the invasive range which have reported very low levels of clonal diversity and extensive geographic areas of genetic uniformity.
Collapse
Affiliation(s)
- Nicolay Leme da Cunha
- Grupo de Ecología de la Polinización, INIBIOMA, CONICET-Universidad Nacional del Comahue, San Carlos de Bariloche, Rio Negro, Argentina.,Programa de Pós-Graduação em Ecologia e Conservação, Universidade Federal de Mato Grosso do Sul, Campo Grande, Mato Grosso do Sul, Brazil
| | - Haoran Xue
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| |
Collapse
|
7
|
Comparative genome anatomy reveals evolutionary insights into a unique amphitriploid fish. Nat Ecol Evol 2022; 6:1354-1366. [PMID: 35817827 PMCID: PMC9439954 DOI: 10.1038/s41559-022-01813-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 05/25/2022] [Indexed: 12/21/2022]
Abstract
Triploids are rare in nature because of difficulties in meiotic and gametogenic processes, especially in vertebrates. The Carassius complex of cyprinid teleosts contains sexual tetraploid crucian carp/goldfish (C. auratus) and unisexual hexaploid gibel carp/Prussian carp (C. gibelio) lineages, providing a valuable model for studying the evolution and maintenance mechanism of unisexual polyploids in vertebrates. Here we sequence the genomes of the two species and assemble their haplotypes, which contain two subgenomes (A and B), to the chromosome level. Sequencing coverage analysis reveals that C. gibelio is an amphitriploid (AAABBB) with two triploid sets of chromosomes; each set is derived from a different ancestor. Resequencing data from different strains of C. gibelio show that unisexual reproduction has been maintained for over 0.82 million years. Comparative genomics show intensive expansion and alterations of meiotic cell cycle-related genes and an oocyte-specific histone variant. Cytological assays indicate that C. gibelio produces unreduced oocytes by an alternative ameiotic pathway; however, sporadic homologous recombination and a high rate of gene conversion also exist in C. gibelio. These genomic changes might have facilitated purging deleterious mutations and maintaining genome stability in this unisexual amphitriploid fish. Overall, the current results provide novel insights into the evolutionary mechanisms of the reproductive success in unisexual polyploid vertebrates. Genome sequencing and haplotype assembly of two cyprinid teleosts, a sexual tetraploid and an unisexual hexaploid, reveal insights into the evolutionary mechanisms underpinning the reproductive success of unisexual polyploid vertebrates.
Collapse
|
8
|
Barnard-Kubow KB, Becker D, Murray CS, Porter R, Gutierrez G, Erickson P, Nunez JCB, Voss E, Suryamohan K, Ratan A, Beckerman A, Bergland AO. Genetic Variation in Reproductive Investment Across an Ephemerality Gradient in Daphnia pulex. Mol Biol Evol 2022; 39:msac121. [PMID: 35642301 PMCID: PMC9198359 DOI: 10.1093/molbev/msac121] [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: 11/27/2022] Open
Abstract
Species across the tree of life can switch between asexual and sexual reproduction. In facultatively sexual species, the ability to switch between reproductive modes is often environmentally dependent and subject to local adaptation. However, the ecological and evolutionary factors that influence the maintenance and turnover of polymorphism associated with facultative sex remain unclear. We studied the ecological and evolutionary dynamics of reproductive investment in the facultatively sexual model species, Daphnia pulex. We found that patterns of clonal diversity, but not genetic diversity varied among ponds consistent with the predicted relationship between ephemerality and clonal structure. Reconstruction of a multi-year pedigree demonstrated the coexistence of clones that differ in their investment into male production. Mapping of quantitative variation in male production using lab-generated and field-collected individuals identified multiple putative quantitative trait loci (QTL) underlying this trait, and we identified a plausible candidate gene. The evolutionary history of these QTL suggests that they are relatively young, and male limitation in this system is a rapidly evolving trait. Our work highlights the dynamic nature of the genetic structure and composition of facultative sex across space and time and suggests that quantitative genetic variation in reproductive strategy can undergo rapid evolutionary turnover.
Collapse
Affiliation(s)
- Karen B Barnard-Kubow
- Department of Biology, University of Virginia, Charlottesville, VA, USA
- Department of Biology, James Madison University, Harrisonburg, VA, USA
| | - Dörthe Becker
- Department of Biology, University of Virginia, Charlottesville, VA, USA
- School of Biosciences, Ecology and Evolutionary Biology, University of Sheffield, Sheffield, UK
- Department of Biology, University of Marburg, Marburg, Germany
| | - Connor S Murray
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Robert Porter
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Grace Gutierrez
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | | | - Joaquin C B Nunez
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - Erin Voss
- Department of Biology, University of Virginia, Charlottesville, VA, USA
- Department of Integrative Biology, UC Berkeley, Berkeley, CA, USA
| | | | - Aakrosh Ratan
- Center for Public Health Genomics, University of Virginia, Charlottesville, VA, USA
- Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA
| | - Andrew Beckerman
- School of Biosciences, Ecology and Evolutionary Biology, University of Sheffield, Sheffield, UK
| | - Alan O Bergland
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| |
Collapse
|
9
|
Ohtsuki H, Norimatsu H, Makino T, Urabe J. Invasions of an obligate asexual daphnid species support the nearly neutral theory. Sci Rep 2022; 12:7305. [PMID: 35508526 PMCID: PMC9068809 DOI: 10.1038/s41598-022-11218-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 04/20/2022] [Indexed: 11/09/2022] Open
Abstract
To verify the "nearly neutral theory (NNT)," the ratio of nonsynonymous to synonymous substitutions (dN/dS) was compared among populations of different species. To determine the validity of NNT, however, populations that are genetically isolated from each other but share the same selection agents and differ in size should be compared. Genetically different lineages of obligate asexual Daphnia pulex invading Japan from North America are an ideal example as they satisfy these prerequisites. Therefore, we analyzed the whole-genome sequences of 18 genotypes, including those of the two independently invaded D. pulex lineages (JPN1 and JPN2) and compared the dN/dS ratio between the lineages. The base substitution rate of each genotype demonstrated that the JPN1 lineage having a larger distribution range diverged earlier and thus was older than the JPN2 lineage. Comparisons of the genotypes within lineages revealed that changes in dN/dS occurred after the divergence and were larger in the younger lineage, JPN2. These results imply that the JPN1 lineage has been more effectively subjected to purification selections, while slightly deteriorating mutations are less purged in JPN2 with smaller population size. Altogether, the lineage-specific difference in the dN/dS ratio for the obligate asexual D. pulex was well explained by the NNT.
Collapse
Affiliation(s)
- Hajime Ohtsuki
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Hirotomo Norimatsu
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Takashi Makino
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
| | - Jotaro Urabe
- Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan.
| |
Collapse
|
10
|
Archetti M. Evidence from automixis with inverted meiosis for the maintenance of sex by loss of complementation. J Evol Biol 2021; 35:40-50. [PMID: 34927297 DOI: 10.1111/jeb.13975] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2021] [Revised: 12/10/2021] [Accepted: 12/11/2021] [Indexed: 11/30/2022]
Abstract
The adaptive value of sexual reproduction is still debated. A short-term disadvantage of asexual reproduction is loss of heterozygosity, which leads to the unmasking of recessive deleterious mutations. The cost of this loss of complementation is predicted to be higher than the twofold cost of meiosis for most types of asexual reproduction. Automixis with terminal fusion of sister nuclei is especially vulnerable to the effect of loss of complementation. It is found, however, in some taxa including oribatid mites, the most prominent group of ancient asexuals. Here, I show that automixis with terminal fusion is stable if it is associated with inverted meiosis and that this appears to be the case in nature, notably in oribatid mites. The existence of automixis with terminal fusion, and its co-occurrence with inverted meiosis, therefore, is consistent with the hypothesis that loss of complementation is important in the evolution of sexual reproduction.
Collapse
Affiliation(s)
- Marco Archetti
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania, USA
| |
Collapse
|
11
|
Wiberg RAW, Brand JN, Schärer L. Faster Rates of Molecular Sequence Evolution in Reproduction-Related Genes and in Species with Hypodermic Sperm Morphologies. Mol Biol Evol 2021; 38:5685-5703. [PMID: 34534329 PMCID: PMC8662610 DOI: 10.1093/molbev/msab276] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Sexual selection drives the evolution of many striking behaviors and morphologies and should leave signatures of selection at loci underlying these phenotypes. However, although loci thought to be under sexual selection often evolve rapidly, few studies have contrasted rates of molecular sequence evolution at such loci across lineages with different sexual selection contexts. Furthermore, work has focused on separate sexed animals, neglecting alternative sexual systems. We investigate rates of molecular sequence evolution in hermaphroditic flatworms of the genus Macrostomum. Specifically, we compare species that exhibit contrasting sperm morphologies, strongly associated with multiple convergent shifts in the mating strategy, reflecting different sexual selection contexts. Species donating and receiving sperm in every mating have sperm with bristles, likely to prevent sperm removal. Meanwhile, species that hypodermically inject sperm lack bristles, potentially as an adaptation to the environment experienced by hypodermic sperm. Combining functional annotations from the model, Macrostomum lignano, with transcriptomes from 93 congeners, we find genus-wide faster sequence evolution in reproduction-related versus ubiquitously expressed genes, consistent with stronger sexual selection on the former. Additionally, species with hypodermic sperm morphologies had elevated molecular sequence evolution, regardless of a gene's functional annotation. These genome-wide patterns suggest reduced selection efficiency following shifts to hypodermic mating, possibly due to higher selfing rates in these species. Moreover, we find little evidence for convergent amino acid changes across species. Our work not only shows that reproduction-related genes evolve rapidly also in hermaphroditic animals, but also that well-replicated contrasts of different sexual selection contexts can reveal underappreciated genome-wide effects.
Collapse
Affiliation(s)
- R Axel W Wiberg
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Jeremias N Brand
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| | - Lukas Schärer
- Department of Environmental Sciences, Zoological Institute, University of Basel, Basel, Switzerland
| |
Collapse
|
12
|
Janecka MJ, Rovenolt F, Stephenson JF. How does host social behavior drive parasite non-selective evolution from the within-host to the landscape-scale? Behav Ecol Sociobiol 2021. [DOI: 10.1007/s00265-021-03089-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
13
|
Heywood JS, Smith SA. DOES CLEISTOGAMOUS SELF-FERTILIZATION PROVIDE REPRODUCTIVE ASSURANCE AGAINST SEED PREDATION IN RUELLIA HUMILIS? SOUTHWEST NAT 2021. [DOI: 10.1894/0038-4909-65.2.116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- John S. Heywood
- Department of Biology, Missouri State University, Springfield, MO 65897 (JSH, SAS)
| | - Stephanie A. Smith
- Department of Biology, Missouri State University, Springfield, MO 65897 (JSH, SAS)
| |
Collapse
|
14
|
Hasan AR, Ness RW. Recombination Rate Variation and Infrequent Sex Influence Genetic Diversity in Chlamydomonas reinhardtii. Genome Biol Evol 2021; 12:370-380. [PMID: 32181819 PMCID: PMC7186780 DOI: 10.1093/gbe/evaa057] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/13/2020] [Indexed: 12/12/2022] Open
Abstract
Recombination confers a major evolutionary advantage by breaking up linkage disequilibrium between harmful and beneficial mutations, thereby facilitating selection. However, in species that are only periodically sexual, such as many microbial eukaryotes, the realized rate of recombination is also affected by the frequency of sex, meaning that infrequent sex can increase the effects of selection at linked sites despite high recombination rates. Despite this, the rate of sex of most facultatively sexual species is unknown. Here, we use genomewide patterns of linkage disequilibrium to infer fine-scale recombination rate variation in the genome of the facultatively sexual green alga Chlamydomonas reinhardtii. We observe recombination rate variation of up to two orders of magnitude and find evidence of recombination hotspots across the genome. Recombination rate is highest flanking genes, consistent with trends observed in other nonmammalian organisms, though intergenic recombination rates vary by intergenic tract length. We also find a positive relationship between nucleotide diversity and physical recombination rate, suggesting a widespread influence of selection at linked sites in the genome. Finally, we use estimates of the effective rate of recombination to calculate the rate of sex that occurs in natural populations, estimating a sexual cycle roughly every 840 generations. We argue that the relatively infrequent rate of sex and large effective population size creates a population genetic environment that increases the influence of selection on linked sites across the genome.
Collapse
Affiliation(s)
- Ahmed R Hasan
- Department of Cell and Systems Biology, University of Toronto, Ontario, Canada.,Department of Biology, University of Toronto Mississauga, Ontario, Canada
| | - Rob W Ness
- Department of Cell and Systems Biology, University of Toronto, Ontario, Canada.,Department of Biology, University of Toronto Mississauga, Ontario, Canada
| |
Collapse
|
15
|
Rossetto M, Yap JYS, Lemmon J, Bain D, Bragg J, Hogbin P, Gallagher R, Rutherford S, Summerell B, Wilson TC. A conservation genomics workflow to guide practical management actions. Glob Ecol Conserv 2021. [DOI: 10.1016/j.gecco.2021.e01492] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
|
16
|
Peniston JH, Barfield M, Holt RD, Orive ME. Environmental fluctuations dampen the effects of clonal reproduction on evolutionary rescue. J Evol Biol 2021; 34:710-722. [PMID: 33682225 DOI: 10.1111/jeb.13778] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 01/19/2021] [Accepted: 02/22/2021] [Indexed: 12/27/2022]
Abstract
Evolutionary rescue occurs when genetic change allows a population to persist in response to an environmental change that would otherwise have led to extinction. Most studies of evolutionary rescue assume that species have either fully clonal or fully sexual reproduction; however, many species have partially clonal reproductive strategies in which they reproduce both clonally and sexually. Furthermore, the few evolutionary rescue studies that have evaluated partially clonal reproduction did not consider fluctuations in the environment, which are nearly ubiquitous in nature. Here, we use individual-based simulations to investigate how environmental fluctuations (either uncorrelated or positively autocorrelated) influence the effect of clonality on evolutionary rescue. We show that, for moderate magnitudes of environmental fluctuations, as was found in the absence of fluctuations, increasing the degree of clonality increases the probability of population persistence in response to an abrupt environmental change, but decreases persistence in response to a continuous, directional environmental change. However, with large magnitudes of fluctuations, both the benefits of clonality following a step change and the detrimental effects of clonality following a continuous, directional change are generally reduced; in fact, in the latter scenario, increasing clonality can even become beneficial if environmental fluctuations are autocorrelated. We also show that increased generational overlap dampens the effects of environmental fluctuations. Overall, we demonstrate that understanding the evolutionary rescue of partially clonal organisms requires not only knowledge of the species life history and the type of environmental change, but also an understanding of the magnitude and autocorrelation of environmental fluctuations.
Collapse
Affiliation(s)
- James H Peniston
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Michael Barfield
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Robert D Holt
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Maria E Orive
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, USA
| |
Collapse
|
17
|
Jullien M, Ronfort J, Gay L. How and When Does Outcrossing Occur in the Predominantly Selfing Species Medicago truncatula? FRONTIERS IN PLANT SCIENCE 2021; 12:619154. [PMID: 33679833 PMCID: PMC7925993 DOI: 10.3389/fpls.2021.619154] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Accepted: 01/19/2021] [Indexed: 06/12/2023]
Abstract
Empirical studies on natural populations of Medicago truncatula revealed selfing rates higher than 80%, but never up to 100%. Similarly, several studies of predominantly selfing species show variability in the level of residual outcrossing between populations and also between temporal samples of the same population. However, these studies measure global selfing rates at the scale of the population and we do not know whether there is intra-population variation and how outcrossing events are distributed, between genotypes, plants, flowers, or seeds. Theoretical studies predict the maintenance of residual outcrossing in highly selfing species due to environmental (e.g., pollen biology) and/or genetic determinants and decompositions of the variation in outcrossing rate using experimental data can be very informative to test these hypotheses. Here, we focus on one natural population of M. truncatula in order to describe precisely its mating system. In particular, we investigated the determinants of the selfing rate by testing for seasonal variations (environmental determinism) and variations between genotypes (genetic determinism). We measured selfing rates in maternal progenies from plants collected widely across a natural population. For each plant, we collected pods from flowers produced at the beginning and at the end of the flowering season to test for a seasonal variation in the outcrossing rate. For each collected offspring, we also estimated the likelihood that it was issued from a self-fertilization event and assessed the genetic component of variation of this mating system measure. We found a significant, albeit small, increase in outcrossing rate in progenies collected at the end [t m = 0.137 (SD = 0.025)] compared to those collected at the beginning [t m = 0.083 (0.016)] of the flowering season. A significant between genotypes variation in selfing rate was also detected, resulting in a heritability of 9% for the rate of residual outcrossing. Altogether, our work shows that despite a predominantly selfing reproductive mode, M. truncatula displays variation in residual outcrossing rate, and that this trait is likely under a complex determinism combining environmental and genetic factors. We discuss the evolutionary implications of our results for the population.
Collapse
|
18
|
Hartfield M. Approximating the Coalescent Under Facultative Sex. J Hered 2021; 112:145-154. [PMID: 33511984 DOI: 10.1093/jhered/esaa036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Accepted: 09/01/2020] [Indexed: 11/14/2022] Open
Abstract
Genome studies of facultative sexual species, which can either reproduce sexually or asexually, are providing insight into the evolutionary consequences of mixed reproductive modes. It is currently unclear to what extent the evolutionary history of facultative sexuals' genomes can be approximated by the standard coalescent, and if a coalescent effective population size Ne exists. Here, I determine if and when these approximations can be made. When sex is frequent (occurring at a frequency much greater than 1/N per reproduction per generation, for N the actual population size), the underlying genealogy can be approximated by the standard coalescent, with a coalescent Ne≈N. When sex is very rare (at frequency much lower than 1/N), approximations for the pairwise coalescent time can be obtained, which is strongly influenced by the frequencies of sex and mitotic gene conversion, rather than N. However, these terms do not translate into a coalescent Ne. These results are used to discuss the best sampling strategies for investigating the evolutionary history of facultative sexual species.
Collapse
Affiliation(s)
- Matthew Hartfield
- Institute of Evolutionary Biology, The University of Edinburgh, Edinburgh, UK
| |
Collapse
|
19
|
Orive ME, Krueger-Hadfield SA. Sex and Asex: A Clonal Lexicon. J Hered 2020; 112:1-8. [PMID: 33336685 DOI: 10.1093/jhered/esaa058] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Accepted: 12/15/2020] [Indexed: 01/05/2023] Open
Abstract
Organisms across the tree of life have complex life cycles that include both sexual and asexual reproduction or that are obligately asexual. These organisms include ecologically dominant species that structure many terrestrial and marine ecosystems, as well as many pathogens, pests, and invasive species. We must consider both the evolution and maintenance of these various reproductive modes and how these modes shape the genetic diversity, adaptive evolution, and ability to persist in the species that exhibit them. Thus, having a common framework is a key aspect of understanding the biodiversity that shapes our planet. In the 2019 AGA President's Symposium, Sex and Asex: The genetics of complex life cycles, researchers investigating a wide range of taxonomic models and using a variety of modes of investigation coalesced around a common theme-understanding not only how such complex life cycles may evolve, but how they are shaped by the evolutionary and ecological forces around them. In this introduction to the Special Issue from the symposium, we give an overview of some of the key ideas and areas of investigation (a common clonal lexicon, we might say) and introduce the breadth of work submitted by symposium participants.
Collapse
Affiliation(s)
- Maria E Orive
- Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Ave., Lawrence, KS 66045
| | - Stacy A Krueger-Hadfield
- Department of Biology, University of Alabama, Birmingham, 1300 University Blvd., Birmingham, AL 35294
| |
Collapse
|
20
|
Cortijo S, Locke JCW. Does Gene Expression Noise Play a Functional Role in Plants? TRENDS IN PLANT SCIENCE 2020; 25:1041-1051. [PMID: 32467064 DOI: 10.1016/j.tplants.2020.04.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 04/22/2020] [Accepted: 04/28/2020] [Indexed: 05/20/2023]
Abstract
Gene expression in individual cells can be surprisingly noisy. In unicellular organisms this noise can be functional; for example, by allowing a subfraction of the population to prepare for environmental stress. The role of gene expression noise in multicellular organisms has, however, remained unclear. In this review, we discuss how new techniques are revealing an unexpected level of variability in gene expression between and within genetically identical plants. We describe recent progress as well as speculate on the function of transcriptional noise as a mechanism for generating functional phenotypic diversity in plants.
Collapse
Affiliation(s)
- Sandra Cortijo
- Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, UK
| | - James C W Locke
- Sainsbury Laboratory, University of Cambridge, Cambridge CB2 1LR, UK.
| |
Collapse
|
21
|
Dalziel AC, Tirbhowan S, Drapeau HF, Power C, Jonah LS, Gbotsyo YA, Dion‐Côté A. Using asexual vertebrates to study genome evolution and animal physiology: Banded ( Fundulus diaphanus) x Common Killifish ( F. heteroclitus) hybrid lineages as a model system. Evol Appl 2020; 13:1214-1239. [PMID: 32684956 PMCID: PMC7359844 DOI: 10.1111/eva.12975] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 03/12/2020] [Accepted: 03/16/2020] [Indexed: 12/27/2022] Open
Abstract
Wild, asexual, vertebrate hybrids have many characteristics that make them good model systems for studying how genomes evolve and epigenetic modifications influence animal physiology. In particular, the formation of asexual hybrid lineages is a form of reproductive incompatibility, but we know little about the genetic and genomic mechanisms by which this mode of reproductive isolation proceeds in animals. Asexual lineages also provide researchers with the ability to produce genetically identical individuals, enabling the study of autonomous epigenetic modifications without the confounds of genetic variation. Here, we briefly review the cellular and molecular mechanisms leading to asexual reproduction in vertebrates and the known genetic and epigenetic consequences of the loss of sex. We then specifically discuss what is known about asexual lineages of Fundulus diaphanus x F. heteroclitus to highlight gaps in our knowledge of the biology of these clones. Our preliminary studies of F. diaphanus and F. heteroclitus karyotypes from Porter's Lake (Nova Scotia, Canada) agree with data from other populations, suggesting a conserved interspecific chromosomal arrangement. In addition, genetic analyses suggest that: (a) the same major clonal lineage (Clone A) of F. diaphanus x F. heteroclitus has remained dominant over the past decade, (b) some minor clones have also persisted, (c) new clones may have recently formed, and iv) wild clones still mainly descend from F. diaphanus ♀ x F. heteroclitus ♂ crosses (96% in 2017-2018). These data suggest that clone formation may be a relatively rare, but continuous process, and there are persistent environmental or genetic factors causing a bias in cross direction. We end by describing our current research on the genomic causes and consequences of a transition to asexuality and the potential physiological consequences of epigenetic variation.
Collapse
Affiliation(s)
| | - Svetlana Tirbhowan
- Department of BiologySaint Mary's UniversityHalifaxNSCanada
- Département de biologieUniversité de MonctonMonctonNBCanada
| | | | - Claude Power
- Département de biologieUniversité de MonctonMonctonNBCanada
| | | | | | | |
Collapse
|
22
|
Wilken SE, Seppälä S, Lankiewicz TS, Saxena M, Henske JK, Salamov AA, Grigoriev IV, O’Malley MA. Genomic and proteomic biases inform metabolic engineering strategies for anaerobic fungi. Metab Eng Commun 2020; 10:e00107. [PMID: 31799118 PMCID: PMC6883316 DOI: 10.1016/j.mec.2019.e00107] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2019] [Revised: 10/24/2019] [Accepted: 11/04/2019] [Indexed: 12/22/2022] Open
Abstract
Anaerobic fungi (Neocallimastigomycota) are emerging non-model hosts for biotechnology due to their wealth of biomass-degrading enzymes, yet tools to engineer these fungi have not yet been established. Here, we show that the anaerobic gut fungi have the most GC depleted genomes among 443 sequenced organisms in the fungal kingdom, which has ramifications for heterologous expression of genes as well as for emerging CRISPR-based genome engineering approaches. Comparative genomic analyses suggest that anaerobic fungi may contain cellular machinery to aid in sexual reproduction, yet a complete mating pathway was not identified. Predicted proteomes of the anaerobic fungi also contain an unusually large fraction of proteins with homopolymeric amino acid runs consisting of five or more identical consecutive amino acids. In particular, threonine runs are especially enriched in anaerobic fungal carbohydrate active enzymes (CAZymes) and this, together with a high abundance of predicted N-glycosylation motifs, suggests that gut fungal CAZymes are heavily glycosylated, which may impact heterologous production of these biotechnologically useful enzymes. Finally, we present a codon optimization strategy to aid in the development of genetic engineering tools tailored to these early-branching anaerobic fungi.
Collapse
Affiliation(s)
- St. Elmo Wilken
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Susanna Seppälä
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Thomas S. Lankiewicz
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
- Department of Evolution Ecology and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
| | - Mohan Saxena
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - John K. Henske
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Asaf A. Salamov
- US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Igor V. Grigoriev
- US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Michelle A. O’Malley
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| |
Collapse
|
23
|
Mattila TM, Laenen B, Slotte T. Population Genomics of Transitions to Selfing in Brassicaceae Model Systems. Methods Mol Biol 2020; 2090:269-287. [PMID: 31975171 DOI: 10.1007/978-1-0716-0199-0_11] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Many plants harbor complex mechanisms that promote outcrossing and efficient pollen transfer. These include floral adaptations as well as genetic mechanisms, such as molecular self-incompatibility (SI) systems. The maintenance of such systems over long evolutionary timescales suggests that outcrossing is favorable over a broad range of conditions. Conversely, SI has repeatedly been lost, often in association with transitions to self-fertilization (selfing). This transition is favored when the short-term advantages of selfing outweigh the costs, primarily inbreeding depression. The transition to selfing is expected to have major effects on population genetic variation and adaptive potential, as well as on genome evolution. In the Brassicaceae, many studies on the population genetic, gene regulatory, and genomic effects of selfing have centered on the model plant Arabidopsis thaliana and the crucifer genus Capsella. The accumulation of population genomics datasets have allowed detailed investigation of where, when and how the transition to selfing occurred. Future studies will take advantage of the development of population genetics theory on the impact of selfing, especially regarding positive selection. Furthermore, investigation of systems including recent transitions to selfing, mixed mating populations and/or multiple independent replicates of the same transition will facilitate dissecting the effects of mating system variation from processes driven by demography.
Collapse
Affiliation(s)
- Tiina M Mattila
- Department of Ecology and Genetics, University of Oulu, Oulu, Finland
| | - Benjamin Laenen
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Tanja Slotte
- Department of Ecology, Environment, and Plant Sciences, Science for Life Laboratory, Stockholm University, Stockholm, Sweden.
| |
Collapse
|
24
|
Kokko H. When Synchrony Makes the Best of Both Worlds Even Better: How Well Do We Really Understand Facultative Sex? Am Nat 2019; 195:380-392. [PMID: 32017623 DOI: 10.1086/706812] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Biological diversity abounds in potential study topics. Studies of model systems have their advantages, but reliance on a few well-understood cases may create false impressions of what biological phenomena are the norm. Here I focus on facultative sex, which is often hailed as offering the best of both worlds, in that rare sex offers benefits almost equal to obligate sex and avoids paying most of the demographic costs. How well do we understand when and why this form of sexual reproduction is expected to prevail? I show several gaps in the theoretical literature and, by contrasting asynchronous with synchronous sex, highlight the need to link sex theories to the theoretical underpinnings of bet hedging, on the one hand, and to mate limitation considerations, on the other. Condition-dependent sex and links between sex with dispersal or dormancy appear understudied. While simplifications are justifiable as a simple assumption structure enhances analytical tractability, much remains to be done to incorporate key features of real sex to the main theoretical edifice.
Collapse
|
25
|
Ho EKH, Bartkowska M, Wright SI, Agrawal AF. Population genomics of the facultatively asexual duckweed Spirodela polyrhiza. THE NEW PHYTOLOGIST 2019; 224:1361-1371. [PMID: 31298732 DOI: 10.1111/nph.16056] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 06/18/2019] [Indexed: 06/10/2023]
Abstract
Clonal propagation allows some plant species to achieve massive population sizes quickly but also reduces the evolutionary independence of different sites in the genome. We examine genome-wide genetic diversity in Spirodela polyrhiza, a duckweed that reproduces primarily asexually. We find that this geographically widespread and numerically abundant species has very low levels of genetic diversity. Diversity at nonsynonymous sites relative to synonymous sites is high, suggesting that purifying selection is weak. A potential explanation for this observation is that a very low frequency of sex renders selection ineffective. However, there is a pronounced decay in linkage disequilibrium over 40 kb, suggesting that though sex may be rare at the individual level it is not too infrequent at the population level. In addition, neutral diversity is affected by the physical proximity of selected sites, which would be unexpected if sex was exceedingly rare at the population level. The amount of genetic mixing as assessed by the decay in linkage disequilibrium is not dissimilar from selfing species such as Arabidopsis thaliana, yet selection appears to be much less effective in duckweed. We discuss alternative explanations for the signature of weak purifying selection.
Collapse
Affiliation(s)
- Eddie K H Ho
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Magdalena Bartkowska
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
- Center for Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Aneil F Agrawal
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
- Center for Analysis of Genome Evolution and Function, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| |
Collapse
|
26
|
Hollister JD, Greiner S, Johnson MTJ, Wright SI. Hybridization and a loss of sex shape genome-wide diversity and the origin of species in the evening primroses (Oenothera, Onagraceae). THE NEW PHYTOLOGIST 2019; 224:1372-1380. [PMID: 31309571 DOI: 10.1111/nph.16053] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 07/02/2019] [Indexed: 06/10/2023]
Abstract
Hybridization is thought to promote speciation in at least two ways - by fixation of heterozygosity from diploid progenitors in allopolyploids, and by generation of transgressive phenotypes and shifting fitness optima during homoploid hybrid speciation. While recent studies support a hybrid origin for a growing number of species, the extent to which hybrid origins shape patterns of diversity in asexual species remains underexplored. Here we employed transcriptome sequencing and population genomic analysis to describe patterns of genomic variation in the 13 species belonging to Oenothera subsection Oenothera. Eight of these species are functionally asexual and arose by hybrid speciation from parents spanning a range of phylogenetic divergence. We showed that genomic divergence between parents has been retained as heterozygosity in functionally asexual species, and that genome-wide levels of heterozygosity in these asexuals largely reflects the divergence of parental haplotypes coupled with a breakdown in recombination and segregation across the genome. These results show that divergence between parental species and loss of sex in hybrids shape patterns of whole-genome diversity and the origin of asexual species.
Collapse
Affiliation(s)
- Jesse D Hollister
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Stephan Greiner
- Max Planck Institute of Molecular Plant Physiology, Potsdam-Golm, 14476, Germany
| | - Marc T J Johnson
- Department of Biology, University of Toronto Mississauga, Mississauga, ON, L5L 1C6, Canada
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 1A1, Canada
| |
Collapse
|
27
|
Leria L, Vila-Farré M, Solà E, Riutort M. Outstanding intraindividual genetic diversity in fissiparous planarians (Dugesia, Platyhelminthes) with facultative sex. BMC Evol Biol 2019; 19:130. [PMID: 31221097 PMCID: PMC6587288 DOI: 10.1186/s12862-019-1440-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 05/15/2019] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND Predicted genetic consequences of asexuality include high intraindividual genetic diversity (i.e., the Meselson effect) and accumulation of deleterious mutations (i.e., Muller's Ratchet), among others. These consequences have been largely studied in parthenogenetic organisms, but studies on fissiparous species are scarce. Differing from parthenogens, fissiparous organisms inherit part of the soma of the progenitor, including somatic mutations. Thus, in the long term, fissiparous reproduction may also result in genetic mosaicism, besides the presence of the Meselson effect and Muller's Ratchet. Dugesiidae planarians show outstanding regeneration capabilities, allowing them to naturally reproduce by fission, either strictly or combined with sex (facultative). Therefore, they are an ideal model to analyze the genetic footprint of fissiparous reproduction, both when it is alternated with sex and when it is the only mode of reproduction. RESULTS In the present study, we generate and analyze intraindividual cloned data of a nuclear and a mitochondrial gene of sexual, fissiparous and facultative wild populations of the species Dugesia subtentaculata. We find that most individuals, independently of their reproductive strategy, are mosaics. However, the intraindividual haplotype and nucleotide diversity of fissiparous and facultative individuals is significantly higher than in sexual individuals, with no signs of Muller's Ratchet. Finally, we also find that this high intraindividual genetic diversity of fissiparous and facultative individuals is composed by different combinations of ancestral and derived haplotypes of the species. CONCLUSIONS The intraindividual analyses of genetic diversity point out that fissiparous reproduction leaves a very special genetic footprint in individuals, characterized by mosaicism combined with the Meselson effect (named in the present study as the mosaic Meselson effect). Interestingly, the different intraindividual combinations of ancestral and derivate genetic diversity indicate that haplotypes generated during periods of fissiparous reproduction can be also transmitted to the progeny through sexual events, resulting in offspring showing a wide range of genetic diversity and putatively allowing purifying selection to act at both intraindividual and individual level. Further investigations, using Dugesia planarians as model organisms, would be of great value to delve into this new model of genetic evolution by the combination of fission and sex.
Collapse
Affiliation(s)
- Laia Leria
- Department de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona, and Institut de Recerca de la Biodiversitat (IRBio), Barcelona, Catalonia Spain
| | - Miquel Vila-Farré
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Eduard Solà
- Department de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona, and Institut de Recerca de la Biodiversitat (IRBio), Barcelona, Catalonia Spain
| | - Marta Riutort
- Department de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona, and Institut de Recerca de la Biodiversitat (IRBio), Barcelona, Catalonia Spain
| |
Collapse
|
28
|
Clo J, Gay L, Ronfort J. How does selfing affect the genetic variance of quantitative traits? An updated meta-analysis on empirical results in angiosperm species. Evolution 2019; 73:1578-1590. [PMID: 31206658 DOI: 10.1111/evo.13789] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 05/13/2019] [Indexed: 12/21/2022]
Abstract
Most theoretical works predict that selfing should reduce the level of additive genetic variance available for quantitative traits within natural populations. Despite a growing number of quantitative genetic studies undertaken during the last two decades, this prediction is still not well supported empirically. To resolve this issue and confirm or reject theoretical predictions, we reviewed quantitative trait heritability estimates from natural plant populations with different rates of self-fertilization and carried out a meta-analysis. In accordance with models of polygenic traits under stabilizing selection, we found that the fraction of additive genetic variance is negatively correlated with the selfing rate. Although the mating system explains a moderate fraction of the variance, the mean reduction of narrow-sense heritability values between strictly allogamous and predominantly selfing populations is strong, around 60%. Because some nonadditive components of genetic variance become selectable under inbreeding, we determine whether self-fertilization affects the relative contribution of these components to genetic variance by comparing narrow-sense heritability estimates from outcrossing populations with broad-sense heritability estimated in autogamous populations. Results suggest that these nonadditive components of variance may restore some genetic variance in predominantly selfing populations; it remains, however, uncertain how these nonadditive components will contribute to adaptation.
Collapse
Affiliation(s)
- Josselin Clo
- AGAP, Montpellier University, CIRAD, INRA, Montpellier SupAgro, Montpellier, France
| | - Laurène Gay
- AGAP, Montpellier University, CIRAD, INRA, Montpellier SupAgro, Montpellier, France
| | - Joëlle Ronfort
- AGAP, Montpellier University, CIRAD, INRA, Montpellier SupAgro, Montpellier, France
| |
Collapse
|
29
|
Bast J, Parker DJ, Dumas Z, Jalvingh KM, Tran Van P, Jaron KS, Figuet E, Brandt A, Galtier N, Schwander T. Consequences of Asexuality in Natural Populations: Insights from Stick Insects. Mol Biol Evol 2019; 35:1668-1677. [PMID: 29659991 PMCID: PMC5995167 DOI: 10.1093/molbev/msy058] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Recombination is a fundamental process with significant impacts on genome evolution. Predicted consequences of the loss of recombination include a reduced effectiveness of selection, changes in the amount of neutral polymorphisms segregating in populations, and an arrest of GC-biased gene conversion. Although these consequences are empirically well documented for nonrecombining genome portions, it remains largely unknown if they extend to the whole genome scale in asexual organisms. We identify the consequences of asexuality using de novo transcriptomes of five independently derived, obligately asexual lineages of stick insects, and their sexual sister-species. We find strong evidence for higher rates of deleterious mutation accumulation, lower levels of segregating polymorphisms and arrested GC-biased gene conversion in asexuals as compared with sexuals. Taken together, our study conclusively shows that predicted consequences of genome evolution under asexuality can indeed be found in natural populations.
Collapse
Affiliation(s)
- Jens Bast
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Darren J Parker
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.,Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Zoé Dumas
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Kirsten M Jalvingh
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Patrick Tran Van
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.,Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Kamil S Jaron
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.,Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Emeric Figuet
- Institute of Evolutionary Sciences, University of Montpellier, CNRS, IRD, EPHE, Montpellier, France
| | - Alexander Brandt
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, University of Goettingen, Goettingen, Germany
| | - Nicolas Galtier
- Institute of Evolutionary Sciences, University of Montpellier, CNRS, IRD, EPHE, Montpellier, France
| | - Tanja Schwander
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| |
Collapse
|
30
|
Dukić M, Berner D, Haag CR, Ebert D. How clonal are clones? A quest for loss of heterozygosity during asexual reproduction in Daphnia magna. J Evol Biol 2019; 32:619-628. [PMID: 30888725 PMCID: PMC6850383 DOI: 10.1111/jeb.13443] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 03/04/2019] [Indexed: 12/25/2022]
Abstract
Due to the lack of recombination, asexual organisms are predicted to accumulate mutations and show high levels of within‐individual allelic divergence (heterozygosity); however, empirical evidence for this prediction is largely missing. Instead, evidence of genome homogenization during asexual reproduction is accumulating. Ameiotic crossover recombination is a mechanism that could lead to long genomic stretches of loss of heterozygosity (LOH) and unmasking of mutations that have little or no effect in heterozygous state. Therefore, LOH might be an important force for inducing variation among asexual offspring and may contribute to the limited longevity of asexual lineages. To investigate the genetic consequences of asexuality, here we used high‐throughput sequencing of Daphnia magna for assessing the rate of LOH over a single generation of asexual reproduction. Comparing parthenogenetic daughters with their mothers at several thousand genetic markers generated by restriction site‐associated DNA (RAD) sequencing resulted in high LOH rate estimation that largely overlapped with our estimates for the error rate. To distinguish these two, we Sanger re‐sequenced the top 17 candidate RAD‐loci for LOH, and all of them proved to be false positives. Hence, even though we cannot exclude the possibility that short stretches of LOH occur in genomic regions not covered by our markers, we conclude that LOH does not occur frequently during asexual reproduction in D. magna and ameiotic crossovers are very rare or absent. This finding suggests that clonal lineages of D. magna will remain genetically homogeneous at least over time periods typically relevant for experimental work.
Collapse
Affiliation(s)
- Marinela Dukić
- Zoological Institute, University of Basel, Basel, Switzerland.,Department of Cell and Developmental Biology, John Innes Centre, Norwich Research Park, Norwich, UK
| | - Daniel Berner
- Zoological Institute, University of Basel, Basel, Switzerland
| | - Christoph R Haag
- Centre d'Ecologie Fonctionnelle et Evolutive-CEFE UMR 5175, CNRS-Université de Montpellier-Université Paul-Valéry Montpellier-EPHE, campus CNRS, Montpellier, France.,Department of Biology, Ecology and Evolution, University of Fribourg, Fribourg, Switzerland
| | - Dieter Ebert
- Zoological Institute, University of Basel, Basel, Switzerland
| |
Collapse
|
31
|
Brandt A, Bast J, Scheu S, Meusemann K, Donath A, Schütte K, Machida R, Kraaijeveld K. No signal of deleterious mutation accumulation in conserved gene sequences of extant asexual hexapods. Sci Rep 2019; 9:5338. [PMID: 30926861 PMCID: PMC6441085 DOI: 10.1038/s41598-019-41821-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 03/18/2019] [Indexed: 11/15/2022] Open
Abstract
Loss of sex and recombination is generally assumed to impede the effectiveness of purifying selection and to result in the accumulation of slightly deleterious mutations. Empirical evidence for this has come from several studies investigating mutational load in a small number of individual genes. However, recent whole transcriptome based studies have yielded inconsistent results, hence questioning the validity of the assumption of mutational meltdown in asexual populations. Here, we study the effectiveness of purifying selection in eight asexual hexapod lineages and their sexual relatives, as present in the 1 K Insect Transcriptome Evolution (1KITE) project, covering eight hexapod groups. We analyse the accumulation of slightly deleterious nonsynonymous and synonymous point mutations in 99 single copy orthologue protein-coding loci shared among the investigated taxa. While accumulation rates of nonsynonymous mutations differed between genes and hexapod groups, we found no effect of reproductive mode on the effectiveness of purifying selection acting at nonsynonymous and synonymous sites. Although the setup of this study does not fully rule out nondetection of subtle effects, our data does not support the established consensus of asexual lineages undergoing ‘mutational meltdown’.
Collapse
Affiliation(s)
- Alexander Brandt
- University of Göttingen, JF Blumenbach Institute of Zoology and Anthropology, Untere Karspüle 2, D-37073, Göttingen, Germany.
| | - Jens Bast
- University of Lausanne, Department of Ecology and Evolution, UNIL Sorge, Le Biophore, CH-1015, Lausanne, Switzerland
| | - Stefan Scheu
- University of Göttingen, JF Blumenbach Institute of Zoology and Anthropology, Untere Karspüle 2, D-37073, Göttingen, Germany
| | - Karen Meusemann
- University of Freiburg, Biology I, Evolutionary Biology & Ecology, Hauptstraße 1, D-79104, Freiburg, Germany.,Center for Molecular Biodiversity Research (ZMB), Zoological Research Museum Alexander König, Adenauerallee 160, D-53113, Bonn, Germany
| | - Alexander Donath
- Center for Molecular Biodiversity Research (ZMB), Zoological Research Museum Alexander König, Adenauerallee 160, D-53113, Bonn, Germany
| | - Kai Schütte
- University of Hamburg, Faculty of Mathematics, Informatics and Natural Sciences, Department of Biology, Institute of Zoology, Research Unit Animal Ecology and Conservation, Martin-Luther-King-Platz 3, D-20146, Hamburg, Germany
| | - Ryuichiro Machida
- Sugadaira Research Station, Mountain Science Center, University of Tsukuba, 1278-294, Sugadaira Kogen, Ueda, Nagano, 386-2204, Japan
| | - Ken Kraaijeveld
- University of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Science Park 904, 1090 GE, Amsterdam, The Netherlands
| |
Collapse
|
32
|
Tvedte ES, Logsdon JM, Forbes AA. Sex loss in insects: causes of asexuality and consequences for genomes. CURRENT OPINION IN INSECT SCIENCE 2019; 31:77-83. [PMID: 31109677 DOI: 10.1016/j.cois.2018.11.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 11/03/2018] [Accepted: 11/20/2018] [Indexed: 06/09/2023]
Abstract
Boasting a staggering diversity of reproductive strategies, insects provide attractive models for the comparative study of the causes and consequences of transitions to asexuality. We provide an overview of some contemporary studies of reproductive systems in insects and compile an initial database of asexual insect genome resources. Insect systems have already yielded some important insights into various mechanisms by which sex is lost, including genetic, endosymbiont-mediated, and hybridization. Studies of mutation and substitution after loss of sex provide the strongest empirical support for hypothesized effects of asexuality, whereas there is mixed evidence for ecological hypotheses such as increased parasite load and altered niche breadth in asexuals. Most hypotheses have been explored in a select few taxa (e.g. stick insects, aphids), such that much of the great taxonomic breadth of insects remain understudied. Given the variation in the proximate causes of asexuality in insects, we argue for expanding the taxonomic breadth of study systems. Despite some challenges for investigating sex in insects, the increasing cost-effectiveness of genomic sequencing makes data generation for closely-related asexual and sexual lineages increasingly feasible.
Collapse
Affiliation(s)
- Eric S Tvedte
- Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD, United States.
| | - John M Logsdon
- Department of Biology, University of Iowa, Iowa City, IA, United States
| | - Andrew A Forbes
- Department of Biology, University of Iowa, Iowa City, IA, United States
| |
Collapse
|
33
|
Freyman WA, Höhna S. Stochastic Character Mapping of State-Dependent Diversification Reveals the Tempo of Evolutionary Decline in Self-Compatible Onagraceae Lineages. Syst Biol 2018; 68:505-519. [DOI: 10.1093/sysbio/syy078] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 11/05/2018] [Accepted: 11/13/2018] [Indexed: 11/13/2022] Open
Affiliation(s)
- William A Freyman
- Department of Integrative Biology, University of California, Berkeley, 3040 Valley Life Sciences Building #3140, CA 94720, USA
| | - Sebastian Höhna
- Division of Evolutionary Biology, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, 80539 Munich, Germany
| |
Collapse
|
34
|
Coalescence and Linkage Disequilibrium in Facultatively Sexual Diploids. Genetics 2018; 210:683-701. [PMID: 30097538 DOI: 10.1534/genetics.118.301244] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Accepted: 08/10/2018] [Indexed: 01/26/2023] Open
Abstract
Under neutrality, linkage disequilibrium results from physically linked sites having nonindependent coalescent histories. In obligately sexual organisms, meiotic recombination is the dominant force separating linked variants from one another, and thus in determining the decay of linkage disequilibrium with physical distance. In facultatively sexual diploid organisms that principally reproduce clonally, mechanisms of mitotic exchange are expected to become relatively more important in shaping linkage disequilibrium. Here we outline mathematical and computational models of a facultative-sex coalescent process that includes meiotic and mitotic recombination, via both crossovers and gene conversion, to determine how linkage disequilibrium is affected with facultative sex. We demonstrate that the degree to which linkage disequilibrium is broken down by meiotic recombination simply scales with the probability of sex if it is sufficiently high (much greater than [Formula: see text] for population size N). However, with very rare sex (occurring with frequency on the order of [Formula: see text]), mitotic gene conversion plays a particularly important and complicated role because it both breaks down associations between sites and removes within-individual diversity. Strong population structure under rare sex leads to lower average linkage disequilibrium values than in panmictic populations, due to the influence of low-frequency polymorphisms created by allelic sequence divergence acting in individual subpopulations. These analyses provide information on how to interpret observed linkage disequilibrium patterns in facultative sexuals and to determine what genomic forces are likely to shape them.
Collapse
|
35
|
Castillo JM, Gallego-Tévar B, Figueroa E, Grewell BJ, Vallet D, Rousseau H, Keller J, Lima O, Dréano S, Salmon A, Aïnouche M. Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific coast of North America. Ecol Evol 2018; 8:4992-5007. [PMID: 29876076 PMCID: PMC5980529 DOI: 10.1002/ece3.4063] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 03/06/2018] [Accepted: 03/15/2018] [Indexed: 02/06/2023] Open
Abstract
Species can respond to environmental pressures through genetic and epigenetic changes and through phenotypic plasticity, but few studies have evaluated the relationships between genetic differentiation and phenotypic plasticity of plant species along changing environmental conditions throughout wide latitudinal ranges. We studied inter‐ and intrapopulation genetic diversity (using simple sequence repeats and chloroplast DNA sequencing) and inter‐ and intrapopulation phenotypic variability of 33 plant traits (using field and common‐garden measurements) for five populations of the invasive cordgrass Spartina densiflora Brongn. along the Pacific coast of North America from San Francisco Bay to Vancouver Island. Studied populations showed very low genetic diversity, high levels of phenotypic variability when growing in contrasted environments and high intrapopulation phenotypic variability for many plant traits. This intrapopulation phenotypic variability was especially high, irrespective of environmental conditions, for those traits showing also high phenotypic plasticity. Within‐population variation represented 84% of the total genetic variation coinciding with certain individual plants keeping consistent responses for three plant traits (chlorophyll b and carotenoid contents, and dead shoot biomass) in the field and in common‐garden conditions. These populations have most likely undergone genetic bottleneck since their introduction from South America; multiple introductions are unknown but possible as the population from Vancouver Island was the most recent and one of the most genetically diverse. S. densiflora appears as a species that would not be very affected itself by climate change and sea‐level rise as it can disperse, establish, and acclimate to contrasted environments along wide latitudinal ranges.
Collapse
Affiliation(s)
- Jesús M Castillo
- Departamento de Biología Vegetal y Ecología Universidad de Sevilla Sevilla Spain
| | - Blanca Gallego-Tévar
- Departamento de Biología Vegetal y Ecología Universidad de Sevilla Sevilla Spain
| | - Enrique Figueroa
- Departamento de Biología Vegetal y Ecología Universidad de Sevilla Sevilla Spain
| | - Brenda J Grewell
- Department of Plant Sciences MS-4 USDA-ARS Exotic & Invasive Weeds Research Unit University of California Davis California
| | | | | | - Jean Keller
- UMR CNRS 6553 ECOBIO Université Rennes 1 Rennes France
| | - Oscar Lima
- UMR CNRS 6553 ECOBIO Université Rennes 1 Rennes France
| | - Stéphane Dréano
- Faculté de Médecine Institut de génétique et Développement de Rennes (IGDR) UMR6290, CNRS Université de Rennes1 Rennes France
| | - Armel Salmon
- UMR CNRS 6553 ECOBIO Université Rennes 1 Rennes France
| | | |
Collapse
|
36
|
Abu Awad D, Roze D. Effects of partial selfing on the equilibrium genetic variance, mutation load, and inbreeding depression under stabilizing selection. Evolution 2018; 72:751-769. [DOI: 10.1111/evo.13449] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 01/17/2018] [Indexed: 01/06/2023]
Affiliation(s)
| | - Denis Roze
- CNRS; UMI 3614 Evolutionary Biology and Ecology of Algae,; 29688 Roscoff France
- Sorbonne Universités; UPMC Université Paris VI,; 29688 Roscoff France
| |
Collapse
|
37
|
Fyon F, Lenormand T. Cis-regulator runaway and divergence in asexuals. Evolution 2018; 72:426-439. [DOI: 10.1111/evo.13424] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 12/06/2017] [Accepted: 12/09/2017] [Indexed: 12/26/2022]
Affiliation(s)
- Frédéric Fyon
- CEFE, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD; Montpellier France
| | - Thomas Lenormand
- CEFE, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD; Montpellier France
| |
Collapse
|
38
|
Demography and mating system shape the genome-wide impact of purifying selection in Arabis alpina. Proc Natl Acad Sci U S A 2018; 115:816-821. [PMID: 29301967 DOI: 10.1073/pnas.1707492115] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Plant mating systems have profound effects on levels and structuring of genetic variation and can affect the impact of natural selection. Although theory predicts that intermediate outcrossing rates may allow plants to prevent accumulation of deleterious alleles, few studies have empirically tested this prediction using genomic data. Here, we study the effect of mating system on purifying selection by conducting population-genomic analyses on whole-genome resequencing data from 38 European individuals of the arctic-alpine crucifer Arabis alpina We find that outcrossing and mixed-mating populations maintain genetic diversity at similar levels, whereas highly self-fertilizing Scandinavian A. alpina show a strong reduction in genetic diversity, most likely as a result of a postglacial colonization bottleneck. We further find evidence for accumulation of genetic load in highly self-fertilizing populations, whereas the genome-wide impact of purifying selection does not differ greatly between mixed-mating and outcrossing populations. Our results demonstrate that intermediate levels of outcrossing may allow efficient selection against harmful alleles, whereas demographic effects can be important for relaxed purifying selection in highly selfing populations. Thus, mating system and demography shape the impact of purifying selection on genomic variation in A. alpina These results are important for an improved understanding of the evolutionary consequences of mating system variation and the maintenance of mixed-mating strategies.
Collapse
|
39
|
Gerber N, Kokko H. Sexual conflict and the evolution of asexuality at low population densities. Proc Biol Sci 2017; 283:rspb.2016.1280. [PMID: 27798298 DOI: 10.1098/rspb.2016.1280] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 09/23/2016] [Indexed: 11/12/2022] Open
Abstract
Theories for the evolution of sex rarely include facultatively sexual reproduction. Sexual harassment by males is an underappreciated factor: it should at first sight increase the relative advantage of asexual reproduction by increasing the cost of sex. However, if the same females can perform either sexual or asexual life cycles, then females trying to reproduce asexually may not escape harassment. If resisting male harassment is costly, it might be beneficial for a female to accept a mating and undertake a sexual life cycle rather than 'insist' on an asexual one. We investigate the effects of sexual harassment on the maintenance of sex under different population densities. Our model shows that resisting matings pays off at low population densities, which leads to the complete extinction of males, and thus to the evolution of completely asexual populations. Facultative sex persists in a narrow range of slightly higher densities. At high densities, selection favours giving up resisting male mating attempts and thus sexual reproduction takes over. These interactions between the outcomes of sexual conflict and population density suggest an explanation for the rarity of facultative sex and also patterns of geographical parthenogenesis, where marginal environments with potentially low densities are associated with asexuality.
Collapse
Affiliation(s)
- Nina Gerber
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Hanna Kokko
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| |
Collapse
|
40
|
Nieuwenhuis BPS, James TY. The frequency of sex in fungi. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0540. [PMID: 27619703 DOI: 10.1098/rstb.2015.0540] [Citation(s) in RCA: 94] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/15/2016] [Indexed: 12/16/2022] Open
Abstract
Fungi are a diverse group of organisms with a huge variation in reproductive strategy. While almost all species can reproduce sexually, many reproduce asexually most of the time. When sexual reproduction does occur, large variation exists in the amount of in- and out-breeding. While budding yeast is expected to outcross only once every 10 000 generations, other fungi are obligate outcrossers with well-mixed panmictic populations. In this review, we give an overview of the costs and benefits of sexual and asexual reproduction in fungi, and the mechanisms that evolved in fungi to reduce the costs of either mode. The proximate molecular mechanisms potentiating outcrossing and meiosis appear to be present in nearly all fungi, making them of little use for predicting outcrossing rates, but also suggesting the absence of true ancient asexual lineages. We review how population genetic methods can be used to estimate the frequency of sex in fungi and provide empirical data that support a mixed mode of reproduction in many species with rare to frequent sex in between rounds of mitotic reproduction. Finally, we highlight how these estimates might be affected by the fungus-specific mechanisms that evolved to reduce the costs of sexual and asexual reproduction.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.
Collapse
Affiliation(s)
- Bart P S Nieuwenhuis
- Department of Evolutionary Biology, Uppsala University, Norbyvägen 18D, 752 36 Uppsala, Sweden
| | - Timothy Y James
- Department of Ecology and Evolutionary Biology, University of Michigan, 830 North University, Ann Arbor, MI 48109-1048, USA
| |
Collapse
|
41
|
Hartfield M. On the origin of asexual species by means of hybridization and drift. Mol Ecol 2017; 25:3264-5. [PMID: 27415414 DOI: 10.1111/mec.13713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Accepted: 05/24/2016] [Indexed: 02/02/2023]
Abstract
Several species of asexuals appear to have existed for millions of years. This is despite the prevalent view that natural selection is weakened without gene exchange, which should cause these organisms to rapidly go extinct. In theory, one can identify evolutionary long-lived asexuals from their allelic sequence divergence, also known as the 'Meselson effect', which leads to elevated within-individual diversity. Yet evidence that this phenomenon exists is mixed. Furthermore, several confounding factors can lead to similar outcomes, including the formation of asexual species by hybridization. Disentangling these factors has proved to be tricky, but Ament-Velásquez et al. (2016) have provided an elegant solution in this issue of Molecular Ecology. They studied transcriptomes and mitochondrial DNA from the Lineus genus of nemertean worms, which contains both sexual and asexual types, to first show that the asexual L. pseudolactus is a hybrid between a sexual and an asexual species. After isolating out diversity arising from this hybridization, they find subsequent evidence for the Meselson effect. This study sets a new standard for differentiating between the complex causes and consequences of asexuality.
Collapse
Affiliation(s)
- Matthew Hartfield
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, Canada M5S 3B2.,Bioinformatics Research Centre, University of Aarhus, 8000C, Aarhus, Denmark
| |
Collapse
|
42
|
Brandt A, Schaefer I, Glanz J, Schwander T, Maraun M, Scheu S, Bast J. Effective purifying selection in ancient asexual oribatid mites. Nat Commun 2017; 8:873. [PMID: 29026136 PMCID: PMC5638860 DOI: 10.1038/s41467-017-01002-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 08/08/2017] [Indexed: 11/29/2022] Open
Abstract
Sex is beneficial in the long term because it can prevent mutational meltdown through increased effectiveness of selection. This idea is supported by empirical evidence of deleterious mutation accumulation in species with a recent transition to asexuality. Here, we study the effectiveness of purifying selection in oribatid mites which have lost sex millions of years ago and diversified into different families and species while reproducing asexually. We compare the accumulation of deleterious nonsynonymous and synonymous mutations between three asexual and three sexual lineages using transcriptome data. Contrasting studies of young asexual lineages, we find evidence for strong purifying selection that is more effective in asexual as compared to sexual oribatid mite lineages. Our results suggest that large populations likely sustain effective purifying selection and facilitate the escape of mutational meltdown in the absence of sex. Thus, sex per se is not a prerequisite for the long-term persistence of animal lineages. Asexual reproduction is thought to be an evolutionary dead end in eukaryotes because deleterious mutations will not be purged effectively. Here, Brandt and colleagues show that anciently asexual oribatid mites in fact have reduced accumulation of deleterious mutations compared to their sexual relatives.
Collapse
Affiliation(s)
- Alexander Brandt
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany.
| | - Ina Schaefer
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany
| | - Julien Glanz
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany
| | - Tanja Schwander
- Department of Ecology and Evolution, University of Lausanne, UNIL Sorge, Le Biophore, CH-1015, Lausanne, Switzerland
| | - Mark Maraun
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany
| | - Stefan Scheu
- Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany.,Center of Biodiversity and Sustainable Land Use, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany
| | - Jens Bast
- Department of Ecology and Evolution, University of Lausanne, UNIL Sorge, Le Biophore, CH-1015, Lausanne, Switzerland.
| |
Collapse
|
43
|
Detwiler JT, Caballero IC, Criscione CD. Role of parasite transmission in promoting inbreeding: I. Infection intensities drive individual parasite selfing rates. Mol Ecol 2017. [DOI: 10.1111/mec.14211] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
|
44
|
Hoang HD, Miller MA. Chemosensory and hyperoxia circuits in C. elegans males influence sperm navigational capacity. PLoS Biol 2017; 15:e2002047. [PMID: 28662030 PMCID: PMC5490939 DOI: 10.1371/journal.pbio.2002047] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 05/25/2017] [Indexed: 11/23/2022] Open
Abstract
The sperm’s crucial function is to locate and fuse with a mature oocyte. Under laboratory conditions, Caenorhabditis elegans sperm are very efficient at navigating the hermaphrodite reproductive tract and locating oocytes. Here, we identify chemosensory and oxygen-sensing circuits that affect the sperm’s navigational capacity. Multiple Serpentine Receptor B (SRB) chemosensory receptors regulate Gα pathways in gustatory sensory neurons that extend cilia through the male nose. SRB signaling is necessary and sufficient in these sensory neurons to influence sperm motility parameters. The neuropeptide Y pathway acts together with SRB-13 to antagonize negative effects of the GCY-35 hyperoxia sensor on spermatogenesis. SRB chemoreceptors are not essential for sperm navigation under low oxygen conditions that C. elegans prefers. In ambient oxygen environments, SRB-13 signaling impacts gene expression during spermatogenesis and the sperm’s mitochondria, thereby increasing migration velocity and inhibiting reversals within the hermaphrodite uterus. The SRB-13 transcriptome is highly enriched in genes implicated in pathogen defense, many of which are expressed in diverse tissues. We show that the critical time period for SRB-13 signaling is prior to spermatocyte differentiation. Our results support the model that young C. elegans males sense external environment and oxygen tension, triggering long-lasting downstream signaling events with effects on the sperm’s mitochondria and navigational capacity. Environmental exposures early in male life may alter sperm function and fertility. Habitat loss, disease, climate change, and pollution are thought to negatively affect animal fertility. Sperm are a potential target, but the molecular mechanisms are not understood. The nematode C. elegans is a powerful genetic model to investigate the relationship between environment and male fertility. The hermaphrodite’s transparent epidermis permits the direct visualization of migrating male sperm and fertilization. In this study, we identified multiple serpentine receptor B (SRB) chemosensory receptors that are expressed in amphid sensory neurons, which extend cilia through the male nose. These SRB chemoreceptors are necessary to produce sperm that are efficient at navigating the hermaphrodite reproductive tract to the fertilization site. We show that SRB-13 signaling counteracts the negative effect of GCY-35 O2 sensor activity, thereby maintaining sperm mitochondrial function and navigational capacity in hyperoxic conditions. Of particular interest, SRB-13 acts in early larval stage males prior to testis maturation. We propose that young males respond to specific stressful environments by altering SRB neural circuits, which in turn impact sperm mitochondrial function and motility. This chemosensory mechanism may be part of a systemic response in C. elegans males to external environment and oxygen levels.
Collapse
Affiliation(s)
- Hieu D. Hoang
- Department of Cell, Developmental and Integrative Biology, University of Alabama School of Medicine, Birmingham, Alabama, United States of America
| | - Michael A. Miller
- Department of Cell, Developmental and Integrative Biology, University of Alabama School of Medicine, Birmingham, Alabama, United States of America
- * E-mail:
| |
Collapse
|
45
|
Ho EKH, Agrawal AF. Aging asexual lineages and the evolutionary maintenance of sex. Evolution 2017; 71:1865-1875. [PMID: 28444897 DOI: 10.1111/evo.13260] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Revised: 04/13/2017] [Accepted: 04/17/2017] [Indexed: 12/24/2022]
Abstract
Finite populations of asexual and highly selfing species suffer from a reduced efficacy of selection. Such populations are thought to decline in fitness over time due to accumulating slightly deleterious mutations or failing to adapt to changing conditions. These within-population processes that lead nonrecombining species to extinction may help maintain sex and outcrossing through species level selection. Although inefficient selection is proposed to elevate extinction rates over time, previous models of species selection for sex assumed constant diversification rates. For sex to persist, classic models require that asexual species diversify at rates lower than sexual species; the validity of this requirement is questionable, both conceptually and empirically. We extend past models by allowing asexual lineages to decline in diversification rates as they age, that is nonrecombining lineages "senesce" in diversification rates. At equilibrium, senescing diversification rates maintain sex even when asexual lineages, at young ages, diversify faster than their sexual progenitors. In such cases, the age distribution of asexual lineages contains a peak at intermediate values rather than showing the exponential decline predicted by the classic model. Coexistence requires only that the average rate of diversification in asexuals be lower than that of sexuals.
Collapse
Affiliation(s)
- Eddie K H Ho
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
| | - Aneil F Agrawal
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3B2, Canada
| |
Collapse
|
46
|
Hartfield M, Bataillon T, Glémin S. The Evolutionary Interplay between Adaptation and Self-Fertilization. Trends Genet 2017; 33:420-431. [PMID: 28495267 PMCID: PMC5450926 DOI: 10.1016/j.tig.2017.04.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Revised: 03/31/2017] [Accepted: 04/03/2017] [Indexed: 11/29/2022]
Abstract
Genome-wide surveys of nucleotide polymorphisms, obtained from next-generation sequencing, have uncovered numerous examples of adaptation in self-fertilizing organisms, especially regarding changes to climate, geography, and reproductive systems. Yet existing models for inferring attributes of adaptive mutations often assume idealized outcrossing populations, which risks mischaracterizing properties of these variants. Recent theoretical work is emphasizing how various aspects of self-fertilization affects adaptation, yet empirical data on these properties are lacking. We review theoretical and empirical studies demonstrating how self-fertilization alters the process of adaptation, illustrated using examples from current sequencing projects. We propose ideas for how future research can more accurately quantify aspects of adaptation in self-fertilizers, including incorporating the effects of standing variation, demographic history, and polygenic adaptation. Analysis of large-scale next-generation sequencing datasets are finding more examples of adaptive evolution at the genomic level. Advances in theoretical work has demonstrated how self-fertilisation affects different aspects of adaptation in these organisms, compared to outcrossers. Current software and statistical methods do not take different mating systems into account, which risks mischaracterising the presence or strength of adaptive mutations from genome scans. Development of new mathematical and statistical methods that explicitly consider self-fertilization and associated demographic effects will enable researchers to more accurately quantify adaptation in these organisms.
Collapse
Affiliation(s)
- Matthew Hartfield
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto ON, Canada M5S 3B2; Bioinformatics Research Centre, Aarhus University, 8000C, Aarhus, Denmark.
| | - Thomas Bataillon
- Bioinformatics Research Centre, Aarhus University, 8000C, Aarhus, Denmark
| | - Sylvain Glémin
- Institut des Sciences de l'Evolution (ISEM - UMR 5554 Universite de Montpellier-CNRS-IRD-EPHE), Place Eugene Bataillon, 34075 Montpellier, France; Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, SE-752 36 Uppsala, Sweden
| |
Collapse
|
47
|
Landscape Genomics of Angiosperm Trees: From Historic Roots to Discovering New Branches of Adaptive Evolution. COMPARATIVE AND EVOLUTIONARY GENOMICS OF ANGIOSPERM TREES 2017. [DOI: 10.1007/7397_2016_19] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
|
48
|
Koch H, Becks L. The consequences of facultative sex in a prey adapting to predation. J Evol Biol 2016; 30:210-220. [DOI: 10.1111/jeb.12987] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Revised: 09/28/2016] [Accepted: 09/29/2016] [Indexed: 10/20/2022]
Affiliation(s)
- H. Koch
- Community Dynamics Group; Department Evolutionary Ecology; Max Planck Institute for Evolutionary Biology; Plön Germany
| | - L. Becks
- Community Dynamics Group; Department Evolutionary Ecology; Max Planck Institute for Evolutionary Biology; Plön Germany
| |
Collapse
|
49
|
Ament-Velásquez SL, Figuet E, Ballenghien M, Zattara EE, Norenburg JL, Fernández-Álvarez FA, Bierne J, Bierne N, Galtier N. Population genomics of sexual and asexual lineages in fissiparous ribbon worms (Lineus, Nemertea): hybridization, polyploidy and the Meselson effect. Mol Ecol 2016; 25:3356-69. [DOI: 10.1111/mec.13717] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Revised: 04/18/2016] [Accepted: 05/02/2016] [Indexed: 12/28/2022]
Affiliation(s)
- S. L. Ament-Velásquez
- Institute of Evolutionary Sciences; University Montpellier; CNRS, IRD, EPHE; Place Eugène Bataillon; 34095 Montpellier France
- Department of Organismal Biology; Systematic Biology; Uppsala University; PO Box 256 SE-751 05 Uppsala Sweden
| | - E. Figuet
- Institute of Evolutionary Sciences; University Montpellier; CNRS, IRD, EPHE; Place Eugène Bataillon; 34095 Montpellier France
| | - M. Ballenghien
- Institute of Evolutionary Sciences; University Montpellier; CNRS, IRD, EPHE; Place Eugène Bataillon; 34095 Montpellier France
| | - E. E. Zattara
- Department of Biology; Indiana University; 107 S Indiana Ave Bloomington IN 47405 USA
- Department of Invertebrate Zoology; National Museum of Natural History; Smithsonian Institution; 10th St. & Constitution Ave. NW Washington DC 20560 USA
| | - J. L. Norenburg
- Department of Invertebrate Zoology; National Museum of Natural History; Smithsonian Institution; 10th St. & Constitution Ave. NW Washington DC 20560 USA
| | | | - J. Bierne
- Laboratoire de Biologie Cellulaire et Moléculaire; Université de Reims Champagne-Ardenne; 9 Boulevard de la Paix 51100 Reims France
| | - N. Bierne
- Institute of Evolutionary Sciences; University Montpellier; CNRS, IRD, EPHE; Place Eugène Bataillon; 34095 Montpellier France
| | - N. Galtier
- Institute of Evolutionary Sciences; University Montpellier; CNRS, IRD, EPHE; Place Eugène Bataillon; 34095 Montpellier France
| |
Collapse
|
50
|
Abstract
Genetic polymorphism varies among species and within genomes, and has important implications for the evolution and conservation of species. The determinants of this variation have been poorly understood, but population genomic data from a wide range of organisms now make it possible to delineate the underlying evolutionary processes, notably how variation in the effective population size (Ne) governs genetic diversity. Comparative population genomics is on its way to providing a solution to 'Lewontin's paradox' - the discrepancy between the many orders of magnitude of variation in population size and the much narrower distribution of diversity levels. It seems that linked selection plays an important part both in the overall genetic diversity of a species and in the variation in diversity within the genome. Genetic diversity also seems to be predictable from the life history of a species.
Collapse
|