1
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Erez K, Jangid A, Feldheim ON, Friedlander T. The role of promiscuous molecular recognition in the evolution of RNase-based self-incompatibility in plants. Nat Commun 2024; 15:4864. [PMID: 38849350 PMCID: PMC11161657 DOI: 10.1038/s41467-024-49163-7] [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: 10/05/2023] [Accepted: 05/22/2024] [Indexed: 06/09/2024] Open
Abstract
How do biological networks evolve and expand? We study these questions in the context of the plant collaborative-non-self recognition self-incompatibility system. Self-incompatibility evolved to avoid self-fertilization among hermaphroditic plants. It relies on specific molecular recognition between highly diverse proteins of two families: female and male determinants, such that the combination of genes an individual possesses determines its mating partners. Though highly polymorphic, previous models struggled to pinpoint the evolutionary trajectories by which new specificities evolved. Here, we construct a novel theoretical framework, that crucially affords interaction promiscuity and multiple distinct partners per protein, as is seen in empirical findings disregarded by previous models. We demonstrate spontaneous self-organization of the population into distinct "classes" with full between-class compatibility and a dynamic long-term balance between class emergence and decay. Our work highlights the importance of molecular recognition promiscuity to network evolvability. Promiscuity was found in additional systems suggesting that our framework could be more broadly applicable.
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Affiliation(s)
- Keren Erez
- The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 7610001, Israel
| | - Amit Jangid
- The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 7610001, Israel
| | - Ohad Noy Feldheim
- The Einstein Institute of Mathematics, Faculty of Natural Sciences, The Hebrew University of Jerusalem, Jerusalem, 9190401, Israel
| | - Tamar Friedlander
- The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot, 7610001, Israel.
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2
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Zeitler L, Parisod C, Gilbert KJ. Purging due to self-fertilization does not prevent accumulation of expansion load. PLoS Genet 2023; 19:e1010883. [PMID: 37656747 PMCID: PMC10501686 DOI: 10.1371/journal.pgen.1010883] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 09/14/2023] [Accepted: 07/25/2023] [Indexed: 09/03/2023] Open
Abstract
As species expand their geographic ranges, colonizing populations face novel ecological conditions, such as new environments and limited mates, and suffer from evolutionary consequences of demographic change through bottlenecks and mutation load accumulation. Self-fertilization is often observed at species range edges and, in addition to countering the lack of mates, is hypothesized as an evolutionary advantage against load accumulation through increased homozygosity and purging. We study how selfing impacts the accumulation of genetic load during range expansion via purging and/or speed of colonization. Using simulations, we disentangle inbreeding effects due to demography versus due to selfing and find that selfers expand faster, but still accumulate load, regardless of mating system. The severity of variants contributing to this load, however, differs across mating system: higher selfing rates purge large-effect recessive variants leaving a burden of smaller-effect alleles. We compare these predictions to the mixed-mating plant Arabis alpina, using whole-genome sequences from refugial outcrossing populations versus expanded selfing populations. Empirical results indicate accumulation of expansion load along with evidence of purging in selfing populations, concordant with our simulations, suggesting that while purging is a benefit of selfing evolving during range expansions, it is not sufficient to prevent load accumulation due to range expansion.
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Affiliation(s)
- Leo Zeitler
- Department of Biology, University of Fribourg, Fribourg, Switzerland
| | - Christian Parisod
- Department of Biology, University of Fribourg, Fribourg, Switzerland
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3
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da Silva VS, Machado CR. Sex in protists: A new perspective on the reproduction mechanisms of trypanosomatids. Genet Mol Biol 2022; 45:e20220065. [PMID: 36218381 PMCID: PMC9552303 DOI: 10.1590/1678-4685-gmb-2022-0065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 08/07/2022] [Indexed: 11/04/2022] Open
Abstract
The Protist kingdom individuals are the most ancestral representatives of eukaryotes. They have inhabited Earth since ancient times and are currently found in the most diverse environments presenting a great heterogeneity of life forms. The unicellular and multicellular algae, photosynthetic and heterotrophic organisms, as well as free-living and pathogenic protozoa represents the protist group. The evolution of sex is directly associated with the origin of eukaryotes being protists the earliest protagonists of sexual reproduction on earth. In eukaryotes, the recombination through genetic exchange is a ubiquitous mechanism that can be stimulated by DNA damage. Scientific evidences support the hypothesis that reactive oxygen species (ROS) induced DNA damage can promote sexual recombination in eukaryotes which might have been a decisive factor for the origin of sex. The fact that some recombination enzymes also participate in meiotic sex in modern eukaryotes reinforces the idea that sexual reproduction emerged as consequence of specific mechanisms to cope with mutations and alterations in genetic material. In this review we will discuss about origin of sex and different strategies of evolve sexual reproduction in some protists such that cause human diseases like malaria, toxoplasmosis, sleeping sickness, Chagas disease, and leishmaniasis.
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Affiliation(s)
- Verônica Santana da Silva
- Universidade Federal de Minas Gerais, Departamento de Genética,
Ecologia e Evolução, Belo Horizonte, MG, Brazil
| | - Carlos Renato Machado
- Universidade Federal de Minas Gerais, Departamento de Bioquímica e
Imunologia, Belo Horizonte, MG, Brazil
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4
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Xu K. The genetic basis of selfing rate evolution. Evolution 2022; 76:883-898. [PMID: 35395695 DOI: 10.1111/evo.14480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 02/02/2022] [Accepted: 02/28/2022] [Indexed: 01/21/2023]
Abstract
Evolution of selfing is common in plant populations, but the genetic basis of selfing rate evolution remains unclear. Although the effects of genetic properties on fixation for mating-unrelated alleles have been investigated, loci that modify the selfing rate (selfing modifiers) differ from mating-unrelated loci in several aspects. Using population genetic models, I investigate the genetic basis of selfing rate evolution. For mating-unrelated alleles, selfing promotes fixation only for recessive mutations, but for selfing modifiers, because the selection coefficient depends on the background selfing rate, selfing can promote fixation even for dominant modifiers. For mating-unrelated alleles, the fixation probability from standing variation is independent of dominance and decreases with an increased background selfing rate. However, for selfing modifiers, the fixation probability peaks at an intermediate selfing rate and when alleles are recessive, because a change of its selection coefficient necessarily involves a change of the inbreeding coefficient, because both depend on the level of inbreeding depression. Furthermore, evolution of selfing involving multiple modifier loci is more likely when selfing is controlled by few large-effect rather than many slight-effect modifiers. I discuss how these characteristics of selfing modifiers have implications for the unidirectional transition from outcrossing to selfing and other empirical patterns.
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Affiliation(s)
- Kuangyi Xu
- Department of Biology, University of North Carolina at Chapel Hill, Coker Hall, 120 South Road, Chapel Hill, North Carolina, 27599, United States
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5
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De Cauwer I, Vernet P, Billiard S, Godé C, Bourceaux A, Ponitzki C, Saumitou-Laprade P. Widespread coexistence of self-compatible and self-incompatible phenotypes in a diallelic self-incompatibility system in Ligustrum vulgare (Oleaceae). Heredity (Edinb) 2021; 127:384-392. [PMID: 34482370 PMCID: PMC8479060 DOI: 10.1038/s41437-021-00463-4] [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: 08/31/2020] [Revised: 07/26/2021] [Accepted: 07/26/2021] [Indexed: 02/07/2023] Open
Abstract
The breakdown of self-incompatibility (SI) in angiosperms is one of the most commonly observed evolutionary transitions. While multiple examples of SI breakdown have been documented in natural populations, there is strikingly little evidence of stable within-population polymorphism with both inbreeding (self-compatible) and outcrossing (self-incompatible) individuals. This absence of breeding system polymorphism corroborates theoretical expectations that predict that in/outbreeding polymorphism is possible only under very restricted conditions. However, theory also predicts that a diallelic sporophytic SI system should facilitate the maintenance of such polymorphism. We tested this prediction by studying the breeding system of Ligustrum vulgare L., an insect-pollinated hermaphroditic species of the Oleaceae family. Using stigma tests with controlled pollination and paternity assignment of open-pollinated progenies, we confirmed the existence of two self-incompatibility groups in this species. We also demonstrated the occurrence of self-compatible individuals in different populations of Western Europe arising from a mutation affecting the functioning of the pollen component of SI. Our results show that the observed low frequency of self-compatible individuals in natural populations is compatible with theoretical predictions only if inbreeding depression is very high.
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Affiliation(s)
- Isabelle De Cauwer
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Philippe Vernet
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Sylvain Billiard
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Cécile Godé
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Angélique Bourceaux
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Chloé Ponitzki
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
| | - Pierre Saumitou-Laprade
- grid.503422.20000 0001 2242 6780Univ. Lille, UMR 8198 – Evo-Eco-Paleo, F-59000 Lille, France ,grid.4444.00000 0001 2112 9282CNRS, UMR 8198, F-59000 Lille, France
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6
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Harkness A, Brandvain Y. Non-self recognition-based self-incompatibility can alternatively promote or prevent introgression. THE NEW PHYTOLOGIST 2021; 231:1630-1643. [PMID: 33533069 DOI: 10.1111/nph.17249] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 01/19/2021] [Indexed: 06/12/2023]
Abstract
Self-incompatibility alleles (S-alleles), which prevent self-fertilisation in plants, have historically been expected to benefit from negative frequency-dependent selection and invade when introduced to a new population through gene flow. However, the most taxonomically widespread form of self-incompatibility, the ribonuclease-based system ancestral to the core eudicots, functions through collaborative non-self recognition, which can affect both short-term patterns of gene flow and the long-term process of S-allele diversification. We analysed a model of S-allele evolution in two populations connected by migration, focussing on comparisons among the fates of S-alleles initially unique to each population and those shared among populations. We found that both shared and unique S-alleles from the population with more unique S-alleles were usually fitter compared with S-alleles from the population with fewer S-alleles. Resident S-alleles often became extinct and were replaced by migrant S-alleles, although this outcome could be averted by pollen limitation or biased migration. Collaborative non-self recognition will usually either result in the whole-sale replacement of S-alleles from one population with those from another or else disfavour introgression of S-alleles altogether.
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Affiliation(s)
- Alexander Harkness
- Department of Ecology, Evolution, and Behavior, University of Minnesota, St Paul, MN, 55108, USA
| | - Yaniv Brandvain
- Department of Plant and Microbial Biology, University of Minnesota, St Paul, MN, 55108, USA
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7
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Broz AK, Simpson-Van Dam A, Tovar-Méndez A, Hahn MW, McClure B, Bedinger PA. Spread of self-compatibility constrained by an intrapopulation crossing barrier. THE NEW PHYTOLOGIST 2021; 231:878-891. [PMID: 33864700 DOI: 10.1111/nph.17400] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2021] [Accepted: 04/09/2021] [Indexed: 06/12/2023]
Abstract
Mating system transitions from self-incompatibility (SI) to self-compatibility (SC) are common in plants. In the absence of high levels of inbreeding depression, SC alleles are predicted to spread due to transmission advantage and reproductive assurance. We characterized mating system and pistil-expressed SI factors in 20 populations of the wild tomato species Solanum habrochaites from the southern half of the species range. We found that a single SI to SC transition is fixed in populations south of the Rio Chillon valley in central Peru. In these populations, SC correlated with the presence of the hab-6 S-haplotype that encodes a low activity S-RNase protein. We identified a single population segregating for SI/SC and hab-6. Intrapopulation crosses showed that hab-6 typically acts in the expected codominant fashion to confer SC. However, we found one specific S-haplotype (hab-10) that consistently rejects pollen of the hab-6 haplotype, and results in SI hab-6/hab-10 heterozygotes. We suggest that the hab-10 haplotype could act as a genetic mechanism to stabilize mixed mating in this population by presenting a disadvantage for the hab-6 haplotype. This barrier may represent a mechanism allowing for the persistence of SI when an SC haplotype appears in or invades a population.
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Affiliation(s)
- Amanda K Broz
- Department of Biology, Colorado State University, Fort Collins, CO, 80523-1878, USA
| | | | | | - Matthew W Hahn
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
- Department of Computer Science, Indiana University, Bloomington, IN, 47405, USA
| | - Bruce McClure
- Department of Biochemistry, University of Missouri-Columbia, Columbia, MO, 65211, USA
| | - Patricia A Bedinger
- Department of Biology, Colorado State University, Fort Collins, CO, 80523-1878, USA
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8
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Harkness A, Goldberg EE, Brandvain Y. Diversification or Collapse of Self-Incompatibility Haplotypes as a Rescue Process. Am Nat 2021; 197:E89-E109. [DOI: 10.1086/712424] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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9
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Encinas-Viso F, Young AG, Pannell JR. The loss of self-incompatibility in a range expansion. J Evol Biol 2020; 33:1235-1244. [PMID: 32557922 DOI: 10.1111/jeb.13665] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 06/09/2020] [Accepted: 06/10/2020] [Indexed: 11/27/2022]
Abstract
It is commonly observed that plant species' range margins are enriched for increased selfing rates and, in otherwise self-incompatible species, for self-compatibility (SC). This has often been attributed to a response to selection under mate and/or pollinator limitation. However, range expansion can also cause reduced inbreeding depression, and this could facilitate the evolution of selfing in the absence of mate or pollinator limitation. Here, we explore this idea using spatially explicit individual-based simulations of a range expansion, in which inbreeding depression, variation in self-incompatibility (SI), and mate availability evolve. Under a wide range of conditions, the simulated range expansion brought about the evolution of selfing after the loss of SI in range-marginal populations. Under conditions of high recombination between the self-incompatibility locus (S-locus) and viability loci, SC remained marginal in the expanded metapopulation and could not invade the range core, which remained self-incompatible. In contrast, under low recombination and migration rates, SC was frequently able to displace SI in the range core by maintaining its association with a genomic background with purged genetic load. We conclude that the evolution of inbreeding depression during a range expansion promotes the evolution of SC at range margins, especially under high rates of recombination..
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Affiliation(s)
- Francisco Encinas-Viso
- Centre for Australian National Biodiversity Research, CSIRO National Research Collections, Canberra, ACT, Australia
| | - Andrew G Young
- Centre for Australian National Biodiversity Research, CSIRO National Research Collections, Canberra, ACT, Australia.,Centre for Biodiversity Analysis, The Australian National University, Canberra, ACT, Australia
| | - John R Pannell
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
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10
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Durand E, Chantreau M, Le Veve A, Stetsenko R, Dubin M, Genete M, Llaurens V, Poux C, Roux C, Billiard S, Vekemans X, Castric V. Evolution of self-incompatibility in the Brassicaceae: Lessons from a textbook example of natural selection. Evol Appl 2020; 13:1279-1297. [PMID: 32684959 PMCID: PMC7359833 DOI: 10.1111/eva.12933] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 01/25/2020] [Accepted: 01/29/2020] [Indexed: 12/14/2022] Open
Abstract
Self-incompatibility (SI) is a self-recognition genetic system enforcing outcrossing in hermaphroditic flowering plants and results in one of the arguably best understood forms of natural (balancing) selection maintaining genetic variation over long evolutionary times. A rich theoretical and empirical population genetics literature has considerably clarified how the distribution of SI phenotypes translates into fitness differences among individuals by a combination of inbreeding avoidance and rare-allele advantage. At the same time, the molecular mechanisms by which self-pollen is specifically recognized and rejected have been described in exquisite details in several model organisms, such that the genotype-to-phenotype map is also pretty well understood, notably in the Brassicaceae. Here, we review recent advances in these two fronts and illustrate how the joint availability of detailed characterization of genotype-to-phenotype and phenotype-to-fitness maps on a single genetic system (plant self-incompatibility) provides the opportunity to understand the evolutionary process in a unique perspective, bringing novel insight on general questions about the emergence, maintenance, and diversification of a complex genetic system.
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Affiliation(s)
| | | | - Audrey Le Veve
- CNRSUniv. LilleUMR 8198 ‐ Evo‐Eco‐PaleoF-59000 LilleFrance
| | | | - Manu Dubin
- CNRSUniv. LilleUMR 8198 ‐ Evo‐Eco‐PaleoF-59000 LilleFrance
| | - Mathieu Genete
- CNRSUniv. LilleUMR 8198 ‐ Evo‐Eco‐PaleoF-59000 LilleFrance
| | - Violaine Llaurens
- Institut de Systématique, Evolution et Biodiversité (ISYEB)Muséum national d'Histoire naturelleCNRS, Sorbonne Université, EPHE, Université des Antilles CP 5057 rue Cuvier, 75005 ParisFrance
| | - Céline Poux
- CNRSUniv. LilleUMR 8198 ‐ Evo‐Eco‐PaleoF-59000 LilleFrance
| | - Camille Roux
- CNRSUniv. LilleUMR 8198 ‐ Evo‐Eco‐PaleoF-59000 LilleFrance
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11
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Krumbeck Y, Constable GWA, Rogers T. Fitness differences suppress the number of mating types in evolving isogamous species. ROYAL SOCIETY OPEN SCIENCE 2020; 7:192126. [PMID: 32257356 PMCID: PMC7062084 DOI: 10.1098/rsos.192126] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 01/31/2020] [Indexed: 06/11/2023]
Abstract
Sexual reproduction is not always synonymous with the existence of two morphologically different sexes; isogamous species produce sex cells of equal size, typically falling into multiple distinct self-incompatible classes, termed mating types. A long-standing open question in evolutionary biology is: what governs the number of these mating types across species? Simple theoretical arguments imply an advantage to rare types, suggesting the number of types should grow consistently; however, empirical observations are very different. While some isogamous species exhibit thousands of mating types, such species are exceedingly rare, and most have fewer than 10. In this paper, we present a mathematical analysis to quantify the role of fitness variation-characterized by different mortality rates-in determining the number of mating types emerging in simple evolutionary models. We predict that the number of mating types decreases as the variance of mortality increases.
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Affiliation(s)
- Yvonne Krumbeck
- Department of Mathematical Sciences, University of Bath, Bath BA2 7AY, UK
| | | | - Tim Rogers
- Department of Mathematical Sciences, University of Bath, Bath BA2 7AY, UK
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12
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Brom T, Castric V, Billiard S. Breakdown of gametophytic self-incompatibility in subdivided populations. Evolution 2020; 74:270-282. [PMID: 31845323 DOI: 10.1111/evo.13897] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 11/04/2019] [Accepted: 11/11/2019] [Indexed: 01/11/2023]
Abstract
In many hermaphroditic flowering plants, self-fertilization is prevented by self-incompatibility (SI), often controlled by a single locus, the S-locus. In single isolated populations, the maintenance of SI depends chiefly on inbreeding depression and the number of SI alleles at the S-locus. In subdivided populations, however, population subdivision has complicated effects on both the number of SI alleles and the level of inbreeding depression, rendering the maintenance of SI difficult to predict. Here, we explore the conditions for the invasion of a self-compatible mutant in a structured population. We find that the maintenance of SI is strongly compromised when a population becomes subdivided. We show that this effect is mainly caused by the decrease in the local diversity of SI alleles rather than by a change in the dynamics of inbreeding depression. Strikingly, we also find that the diversity of SI alleles at the whole population level is a poor predictor of the maintenance of SI. We discuss the implications of our results for the interpretation of empirical data on the loss of SI in natural populations.
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Affiliation(s)
- Thomas Brom
- University Lille, UMR 8198 - Evo-Eco-Paleo, F-59000, Lille, France.,CNRS, UMR 8198, F-59000, Lille, France
| | - Vincent Castric
- University Lille, UMR 8198 - Evo-Eco-Paleo, F-59000, Lille, France.,CNRS, UMR 8198, F-59000, Lille, France
| | - Sylvain Billiard
- University Lille, UMR 8198 - Evo-Eco-Paleo, F-59000, Lille, France.,CNRS, UMR 8198, F-59000, Lille, France
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13
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Czuppon P, Constable GWA. Invasion and Extinction Dynamics of Mating Types Under Facultative Sexual Reproduction. Genetics 2019; 213:567-580. [PMID: 31391266 PMCID: PMC6781889 DOI: 10.1534/genetics.119.302306] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Accepted: 08/04/2019] [Indexed: 01/08/2023] Open
Abstract
In sexually reproducing isogamous species, syngamy between gametes is generally not indiscriminate, but rather restricted to occurring between complementary self-incompatible mating types. A longstanding question regards the evolutionary pressures that control the number of mating types observed in natural populations, which ranges from two to many thousands. Here, we describe a population genetic null model of this reproductive system, and derive expressions for the stationary probability distribution of the number of mating types, the establishment probability of a newly arising mating type, and the mean time to extinction of a resident type. Our results yield that the average rate of sexual reproduction in a population correlates positively with the expected number of mating types observed. We further show that the low number of mating types predicted in the rare-sex regime is primarily driven by low invasion probabilities of new mating type alleles, with established resident alleles being very stable over long evolutionary periods. Moreover, our model naturally exhibits varying selection strength dependent on the number of resident mating types. This results in higher extinction and lower invasion rates for an increasing number of residents.
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Affiliation(s)
- Peter Czuppon
- Center for Interdisciplinary Research in Biology, CNRS, Collège de France, PSL Research University, 75231 Paris, France
- Institute of Ecology and Environmental Sciences of Paris, Sorbonne Université, UPEC, CNRS, IRD, INRA, 75252 Paris, France
| | - George W A Constable
- Department of Mathematical Sciences, The University of Bath, BA2 7AY, United Kingdom
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14
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Bachmann JA, Tedder A, Laenen B, Fracassetti M, Désamoré A, Lafon-Placette C, Steige KA, Callot C, Marande W, Neuffer B, Bergès H, Köhler C, Castric V, Slotte T. Genetic basis and timing of a major mating system shift in Capsella. THE NEW PHYTOLOGIST 2019; 224:505-517. [PMID: 31254395 DOI: 10.1111/nph.16035] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2019] [Accepted: 06/20/2019] [Indexed: 05/23/2023]
Abstract
A crucial step in the transition from outcrossing to self-fertilization is the loss of genetic self-incompatibility (SI). In the Brassicaceae, SI involves the interaction of female and male specificity components, encoded by the genes SRK and SCR at the self-incompatibility locus (S-locus). Theory predicts that S-linked mutations, and especially dominant mutations in SCR, are likely to contribute to loss of SI. However, few studies have investigated the contribution of dominant mutations to loss of SI in wild plant species. Here, we investigate the genetic basis of loss of SI in the self-fertilizing crucifer species Capsella orientalis, by combining genetic mapping, long-read sequencing of complete S-haplotypes, gene expression analyses and controlled crosses. We show that loss of SI in C. orientalis occurred < 2.6 Mya and maps as a dominant trait to the S-locus. We identify a fixed frameshift deletion in the male specificity gene SCR and confirm loss of male SI specificity. We further identify an S-linked small RNA that is predicted to cause dominance of self-compatibility. Our results agree with predictions on the contribution of dominant S-linked mutations to loss of SI, and thus provide new insights into the molecular basis of mating system transitions.
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Affiliation(s)
- Jörg A Bachmann
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Andrew Tedder
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Benjamin Laenen
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Marco Fracassetti
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Aurélie Désamoré
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Clément Lafon-Placette
- Department of Plant Biology, Swedish University of Agricultural Sciences & Linnean Center for Plant Biology, SE-750 07, Uppsala, Sweden
| | - Kim A Steige
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
| | - Caroline Callot
- Institut National de la Recherche Agronomique, UPR 1258, Centre National des Ressources Génomiques Végétales, 31326, Castanet-Tolosan, France
| | - William Marande
- Institut National de la Recherche Agronomique, UPR 1258, Centre National des Ressources Génomiques Végétales, 31326, Castanet-Tolosan, France
| | - Barbara Neuffer
- Department of Botany, University of Osnabruck, 49076, Osnabrück, Germany
| | - Hélène Bergès
- Institut National de la Recherche Agronomique, UPR 1258, Centre National des Ressources Génomiques Végétales, 31326, Castanet-Tolosan, France
| | - Claudia Köhler
- Department of Plant Biology, Swedish University of Agricultural Sciences & Linnean Center for Plant Biology, SE-750 07, Uppsala, Sweden
| | - Vincent Castric
- Univ. Lille, CNRS, UMR 8198 - Evo-Eco-Paleo, F-59000, Lille, France
| | - Tanja Slotte
- Department of Ecology, Environment and Plant Sciences, Science for Life Laboratory, Stockholm University, SE-106 91, Stockholm, Sweden
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15
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Hadjivasiliou Z, Pomiankowski A. Evolution of asymmetric gamete signaling and suppressed recombination at the mating type locus. eLife 2019; 8:48239. [PMID: 31464685 PMCID: PMC6715347 DOI: 10.7554/elife.48239] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 07/25/2019] [Indexed: 11/24/2022] Open
Abstract
The two partners required for sexual reproduction are rarely the same. This pattern extends to species which lack sexual dimorphism yet possess self-incompatible gametes determined at mating-type regions of suppressed recombination, likely precursors of sex chromosomes. Here we investigate the role of cellular signaling in the evolution of mating-types. We develop a model of ligand-receptor dynamics, and identify factors that determine the capacity of cells to send and receive signals. The model specifies conditions favoring the evolution of gametes producing ligand and receptor asymmetrically and shows how these are affected by recombination. When the recombination rate evolves, the conditions favoring asymmetric signaling also favor tight linkage of ligand and receptor loci in distinct linkage groups. These results suggest that selection for asymmetric gamete signaling could be the first step in the evolution of non-recombinant mating-type loci, paving the road for the evolution of anisogamy and sexes. Sexual reproduction, from birds to bees, relies on distinct classes of sex cells, known as gametes, fusing together. Most single cell organisms, rather than producing eggs and sperm, have similar sized gametes that fall into distinct ‘mating types’. However, only sex cells belonging to different mating types can fuse together and sexually reproduce. At first glance, it seems illogical that cells from the same mating type cannot reproduce with each other, as this restricts eligible partners within a population and makes finding a mate more difficult. Yet the typical pattern amongst single cell organisms is still two distinct classes of sex cells, just as in birds and bees. How did the obsession with mating between two different types become favored during evolution? One possibility is that cells with different mating types can recognize and communicate with each other more easily. Cells communicate by releasing proteins known as ligands, which bind to specific receptors found on the cell’s surface. Using mathematical modelling, Hadjivasiliou and Pomiankowski showed that natural selection typically favors ‘asymmetric’ signaling, whereby cells evolve to either produce receptor A with ligand B, or have the reverse pattern and produce receptor B with ligand A. These asymmetric mutants are favored because they avoid producing ligands that clog or activate the receptors on their own surface. As a result, different types of cells are better at recognizing each other and mating more quickly. When cells sexually reproduce they exchange genetic material with each other to produce offspring with a combination of genes that differ to their own. However, if the genes coding for ligand and receptor pairs were constantly being ‘swapped’, this could lead to new combinations, and a loss of asymmetric signaling. Hadjivasiliou and Pomiankowski showed that for asymmetric signaling to evolve, natural selection favors the genes encoding these non-compatible ligand and receptor pairs to be closely linked within the genome. This ensures that the mis-matching ligand and receptor are inherited together, preventing cells from producing pairs which can bind to themselves. This study provides an original way to address an evolutionary question which has long puzzled biologists. These findings raise further questions about how gametes evolved to become the sperm and egg, and how factors such as signaling between cells can determine the sex of more complex organisms, such as ourselves.
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Affiliation(s)
- Zena Hadjivasiliou
- Department of Biochemistry, University of Geneva, Geneva, Switzerland.,Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London, United Kingdom.,Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
| | - Andrew Pomiankowski
- Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London, United Kingdom.,Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
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16
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Voillemot M, Encinas-Viso F, Pannell JR. Rapid loss of self-incompatibility in experimental populations of the perennial outcrossing plant Linaria cavanillesii. Evolution 2019; 73:913-926. [PMID: 30874301 DOI: 10.1111/evo.13721] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 02/18/2019] [Indexed: 11/30/2022]
Abstract
Transitions from self-incompatibility to self-compatibility in angiosperms may be frequently driven by selection for reproductive assurance when mates or pollinators are rare, and are often succeeded by loss of inbreeding depression by purging. Here, we use experimental evolution to investigate the spread of self-compatibility from one such population of the perennial plant Linaria cavanillesii into self-incompatible (SI) populations that still have high inbreeding depression. We introduced self-compatible (SC) individuals at different frequencies into replicate experimental populations of L. cavanillesii that varied in access to pollinators. Our experiment revealed a rapid shift to self-compatibility in all replicates, driven by both greater seed set and greater outcross siring success of SC individuals. We discuss our results in the light of computer simulations that confirm the tendency of self-compatibility to spread into SI populations under the observed conditions. Our study illustrates the ease with which self-compatibility can spread among populations, a requisite for species-wide transitions from self-incompatibility to self-compatibility.
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Affiliation(s)
- Marie Voillemot
- Department of Ecology and Evolution, Biophore/Sorge, University of Lausanne, 1015, Lausanne, Switzerland
| | - Francisco Encinas-Viso
- Centre for Australian National Biodiversity Research, CSIRO, Canberra, ACT 2601, Australia
| | - John R Pannell
- Department of Ecology and Evolution, Biophore/Sorge, University of Lausanne, 1015, Lausanne, Switzerland
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17
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Wu M, Kostyun JL, Moyle LC. Genome Sequence of Jaltomata Addresses Rapid Reproductive Trait Evolution and Enhances Comparative Genomics in the Hyper-Diverse Solanaceae. Genome Biol Evol 2019; 11:335-349. [PMID: 30608583 PMCID: PMC6368146 DOI: 10.1093/gbe/evy274] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2018] [Indexed: 12/11/2022] Open
Abstract
Within the economically important plant family Solanaceae, Jaltomata is a rapidly evolving genus that has extensive diversity in flower size and shape, as well as fruit and nectar color, among its ∼80 species. Here, we report the whole-genome sequencing, assembly, and annotation, of one representative species (Jaltomata sinuosa) from this genus. Combining PacBio long reads (25×) and Illumina short reads (148×) achieved an assembly of ∼1.45 Gb, spanning ∼96% of the estimated genome. Ninety-six percent of curated single-copy orthologs in plants were detected in the assembly, supporting a high level of completeness of the genome. Similar to other Solanaceous species, repetitive elements made up a large fraction (∼80%) of the genome, with the most recently active element, Gypsy, expanding across the genome in the last 1–2 Myr. Computational gene prediction, in conjunction with a merged transcriptome data set from 11 tissues, identified 34,725 protein-coding genes. Comparative phylogenetic analyses with six other sequenced Solanaceae species determined that Jaltomata is most likely sister to Solanum, although a large fraction of gene trees supported a conflicting bipartition consistent with substantial introgression between Jaltomata and Capsicum after these species split. We also identified gene family dynamics specific to Jaltomata, including expansion of gene families potentially involved in novel reproductive trait development, and loss of gene families that accompanied the loss of self-incompatibility. This high-quality genome will facilitate studies of phenotypic diversification in this rapidly radiating group and provide a new point of comparison for broader analyses of genomic evolution across the Solanaceae.
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Affiliation(s)
- Meng Wu
- Department of Biology, Indiana University Bloomington
| | - Jamie L Kostyun
- Department of Biology, Indiana University Bloomington.,Department of Plant Biology, University of Vermont
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18
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Mable BK. Conservation of adaptive potential and functional diversity: integrating old and new approaches. CONSERV GENET 2018. [DOI: 10.1007/s10592-018-1129-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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19
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Layman NC, Busch JW. Bottlenecks and inbreeding depression in autotetraploids. Evolution 2018; 72:2025-2037. [PMID: 30136722 DOI: 10.1111/evo.13587] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 08/14/2018] [Indexed: 12/30/2022]
Abstract
Inbreeding depression is dependent on the ploidy of populations and can inhibit the evolution of selfing. While polyploids should generally harbor less inbreeding depression than diploids at equilibrium, it has been unclear whether this pattern holds in non-equilibrium conditions following bottlenecks. We use stochastic individual-based simulations to determine the effects of population bottlenecks on inbreeding depression in diploids and autotetraploids, in addition to cases where neo-autotetraploids form from the union of unreduced gametes. With a ploidy-independent dominance function based on enzyme kinetics, inbreeding depression is generally lower in autotetraploids for fully and partially recessive mutations. Due to the sampling of more chromosomes during reproduction, bottlenecks generally reduce inbreeding depression to a lesser extent in autotetraploids. All else being equal, population bottlenecks may have ploidy-dependent effects for another reason-in some cases matings between close relatives temporarily increase inbreeding depression in autotetraploids by increasing the frequency of the heterozygous genotype harboring the most harmful mutations. When neo-autotetraploids are formed by few individuals, inbreeding depression is dramatically reduced, given extensive masking of harmful mutations following whole genome duplication. This effect persists as nascent tetraploids reach mutation-selection-drift balance, providing a transient period of permissive conditions favoring the evolution of selfing.
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Affiliation(s)
- Nathan C Layman
- School of Biological Sciences, Washington State University, Pullman, Washington 99164
| | - Jeremiah W Busch
- School of Biological Sciences, Washington State University, Pullman, Washington 99164
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20
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Tsuchimatsu T, Goubet PM, Gallina S, Holl AC, Fobis-Loisy I, Bergès H, Marande W, Prat E, Meng D, Long Q, Platzer A, Nordborg M, Vekemans X, Castric V. Patterns of Polymorphism at the Self-Incompatibility Locus in 1,083 Arabidopsis thaliana Genomes. Mol Biol Evol 2018; 34:1878-1889. [PMID: 28379456 PMCID: PMC5850868 DOI: 10.1093/molbev/msx122] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Although the transition to selfing in the model plant Arabidopsis thaliana involved the loss of the self-incompatibility (SI) system, it clearly did not occur due to the fixation of a single inactivating mutation at the locus determining the specificities of SI (the S-locus). At least three groups of divergent haplotypes (haplogroups), corresponding to ancient functional S-alleles, have been maintained at this locus, and extensive functional studies have shown that all three carry distinct inactivating mutations. However, the historical process of loss of SI is not well understood, in particular its relation with the last glaciation. Here, we took advantage of recently published genomic resequencing data in 1,083 Arabidopsis thaliana accessions that we combined with BAC sequencing to obtain polymorphism information for the whole S-locus region at a species-wide scale. The accessions differed by several major rearrangements including large deletions and interhaplogroup recombinations, forming a set of haplogroups that are widely distributed throughout the native range and largely overlap geographically. “Relict” A. thaliana accessions that directly derive from glacial refugia are polymorphic at the S-locus, suggesting that the three haplogroups were already present when glacial refugia from the last Ice Age became isolated. Interhaplogroup recombinant haplotypes were highly frequent, and detailed analysis of recombination breakpoints suggested multiple independent origins. These findings suggest that the complete loss of SI in A. thaliana involved independent self-compatible mutants that arose prior to the last Ice Age, and experienced further rearrangements during postglacial colonization.
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Affiliation(s)
- Takashi Tsuchimatsu
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria.,Department of Biology, Chiba University, Inage-ku, Chiba, Japan
| | | | - Sophie Gallina
- Université de Lille CNRS, UMR 8198-Evo-Eco-Paleo, Lille, France
| | | | - Isabelle Fobis-Loisy
- Reproduction et Développement des Plantes, Univ. Lyon, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, Université Claude Bernard Lyon I, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Hélène Bergès
- Centre National des Ressources Génomiques Végétales, INRA UPR 1258, Castanet-Tolosan, France
| | - William Marande
- Centre National des Ressources Génomiques Végétales, INRA UPR 1258, Castanet-Tolosan, France
| | - Elisa Prat
- Centre National des Ressources Génomiques Végétales, INRA UPR 1258, Castanet-Tolosan, France
| | - Dazhe Meng
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria
| | - Quan Long
- Department of Biochemistry and Molecular Biology & Cumming School of Medicine, University of Calgary, Calgary, AB, Canada
| | - Alexander Platzer
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria
| | - Magnus Nordborg
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria
| | - Xavier Vekemans
- Université de Lille CNRS, UMR 8198-Evo-Eco-Paleo, Lille, France
| | - Vincent Castric
- Université de Lille CNRS, UMR 8198-Evo-Eco-Paleo, Lille, France
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21
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Voillemot M, Rougemont Q, Roux C, Pannell JR. The divergence history of the perennial plant Linaria cavanillesii
confirms a recent loss of self-incompatibility. J Evol Biol 2017; 31:136-147. [DOI: 10.1111/jeb.13209] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2017] [Revised: 11/03/2017] [Accepted: 11/07/2017] [Indexed: 11/30/2022]
Affiliation(s)
- M. Voillemot
- Department of Ecology and Evolution; Biophore/Sorge; University of Lausanne; Lausanne Switzerland
| | - Q. Rougemont
- Institut de Biologie Intégrative et des Systèmes (IBIS); University of Laval; Québec City Québec Canada
| | - C. Roux
- Department of Ecology and Evolution; Biophore/Sorge; University of Lausanne; Lausanne Switzerland
- Unité Evo-Eco-Paléo (EEP) - UMR 8198; CNRS; Université de Lille Sciences et Technologies; Villeneuve d'Ascq Cedex France
| | - J. R. Pannell
- Department of Ecology and Evolution; Biophore/Sorge; University of Lausanne; Lausanne Switzerland
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22
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Hadjivasiliou Z, Pomiankowski A. Gamete signalling underlies the evolution of mating types and their number. Philos Trans R Soc Lond B Biol Sci 2017; 371:rstb.2015.0531. [PMID: 27619695 PMCID: PMC5031616 DOI: 10.1098/rstb.2015.0531] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/11/2016] [Indexed: 01/02/2023] Open
Abstract
The gametes of unicellular eukaryotes are morphologically identical, but are nonetheless divided into distinct mating types. The number of mating types varies enormously and can reach several thousand, yet most species have only two. Why do morphologically identical gametes need to be differentiated into self-incompatible mating types, and why is two the most common number of mating types? In this work, we explore a neglected hypothesis that there is a need for asymmetric signalling interactions between mating partners. Our review shows that isogamous gametes always interact asymmetrically throughout sex and argue that this asymmetry is favoured because it enhances the efficiency of the mating process. We further develop a simple mathematical model that allows us to study the evolution of the number of mating types based on the strength of signalling interactions between gametes. Novel mating types have an advantage as they are compatible with all others and rarely meet their own type. But if existing mating types coevolve to have strong mutual interactions, this restricts the spread of novel types. Similarly, coevolution is likely to drive out less attractive mating types. These countervailing forces specify the number of mating types that are evolutionarily stable. This article is part of the themed issue ‘Weird sex: the underappreciated diversity of sexual reproduction’.
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Affiliation(s)
- Zena Hadjivasiliou
- Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK
| | - Andrew Pomiankowski
- Centre for Mathematics and Physics in the Life Sciences and Experimental Biology, University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK
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23
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Furstenau TN, Cartwright RA. The impact of self-incompatibility systems on the prevention of biparental inbreeding. PeerJ 2017; 5:e4085. [PMID: 29188143 PMCID: PMC5703146 DOI: 10.7717/peerj.4085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 11/02/2017] [Indexed: 12/05/2022] Open
Abstract
Inbreeding in hermaphroditic plants can occur through two different mechanisms: biparental inbreeding, when a plant mates with a related individual, or self-fertilization, when a plant mates with itself. To avoid inbreeding, many hermaphroditic plants have evolved self-incompatibility (SI) systems which prevent or limit self-fertilization. One particular SI system-homomorphic SI-can also reduce biparental inbreeding. Homomorphic SI is found in many angiosperm species, and it is often assumed that the additional benefit of reduced biparental inbreeding may be a factor in the success of this SI system. To test this assumption, we developed a spatially-explicit, individual-based simulation of plant populations that displayed three different types of homomorphic SI. We measured the total level of inbreeding avoidance by comparing each population to a self-compatible population (NSI), and we measured biparental inbreeding avoidance by comparing to a population of self-incompatible plants that were free to mate with any other individual (PSI). Because biparental inbreeding is more common when offspring dispersal is limited, we examined the levels of biparental inbreeding over a range of dispersal distances. We also tested whether the introduction of inbreeding depression affected the level of biparental inbreeding avoidance. We found that there was a statistically significant decrease in autozygosity in each of the homomorphic SI populations compared to the PSI population and, as expected, this was more pronounced when seed and pollen dispersal was limited. However, levels of homozygosity and inbreeding depression were not reduced. At low dispersal, homomorphic SI populations also suffered reduced female fecundity and had smaller census population sizes. Overall, our simulations showed that the homomorphic SI systems had little impact on the amount of biparental inbreeding in the population especially when compared to the overall reduction in inbreeding compared to the NSI population. With further study, this observation may have important consequences for research into the origin and evolution of homomorphic self-incompatibility systems.
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Affiliation(s)
- Tara N. Furstenau
- The Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, AZ, United States of America
- The School of Informatics, Computing, and Cyber Systems, Northern Arizona University, Flagstaff, AZ, United States of America
| | - Reed A. Cartwright
- The Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, AZ, United States of America
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24
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Two Loci Contribute Epistastically to Heterospecific Pollen Rejection, a Postmating Isolating Barrier Between Species. G3-GENES GENOMES GENETICS 2017; 7:2151-2159. [PMID: 28512086 PMCID: PMC5499124 DOI: 10.1534/g3.117.041673] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recognition and rejection of heterospecific male gametes occurs in a broad range of taxa, although the complexity of mechanisms underlying these components of postmating cryptic female choice is poorly understood. In plants, the arena for postmating interactions is the female reproductive tract (pistil), within which heterospecific pollen tube growth can be arrested via active molecular recognition and rejection. Unilateral incompatibility (UI) is one such postmating barrier in which pollen arrest occurs in only one direction of an interspecific cross. We investigated the genetic basis of pistil-side UI between Solanum species, with the specific goal of understanding the role and magnitude of epistasis between UI QTL. Using heterospecific introgression lines (ILs) between Solanum pennellii and S. lycopersicum, we assessed the individual and pairwise effects of three chromosomal regions (ui1.1, ui3.1, and ui12.1) previously associated with interspecific UI among Solanum species. Specifically, we generated double introgression (‘pyramided’) genotypes that combined ui12.1 with each of ui1.1 and ui3.1, and assessed the strength of UI pollen rejection in the pyramided lines, compared to single introgression genotypes. We found that none of the three QTL individually showed UI rejection phenotypes, but lines combining ui3.1 and ui12.1 showed significant pistil-side pollen rejection. Furthermore, double ILs (DILs) that combined different chromosomal regions overlapping ui3.1 differed significantly in their rate of UI, consistent with at least two genetic factors on chromosome three contributing quantitatively to interspecific pollen rejection. Together, our data indicate that loci on both chromosomes 3 and 12 are jointly required for the expression of UI between S. pennellii and S. lycopersicum, suggesting that coordinated molecular interactions among a relatively few loci underlie the expression of this postmating prezygotic barrier. In addition, in conjunction with previous data, at least one of these loci appears to also contribute to conspecific self-incompatibility (SI), consistent with a partially shared genetic basis between inter- and intraspecific mechanisms of postmating prezygotic female choice.
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25
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Lande R, Schemske DW. THE EVOLUTION OF SELF-FERTILIZATION AND INBREEDING DEPRESSION IN PLANTS. I. GENETIC MODELS. Evolution 2017; 39:24-40. [PMID: 28563655 DOI: 10.1111/j.1558-5646.1985.tb04077.x] [Citation(s) in RCA: 676] [Impact Index Per Article: 96.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/1983] [Revised: 06/22/1984] [Indexed: 11/28/2022]
Abstract
The amounts of inbreeding depression upon selfing and of heterosis upon outcrossing determine the strength of selection on the selfing rate in a population when this evolves polygenically by small steps. Genetic models are constructed which allow inbreeding depression to change with the mean selfing rate in a population by incorporating both mutation to recessive and partially dominant lethal and sublethal alleles at many loci and mutation in quantitative characters under stabilizing selection. The models help to explain observations of high inbreeding depression (> 50%) upon selfing in primarily outcrossing populations, as well as considerable heterosis upon outcrossing in primarily selfing populations. Predominant selfing and predominant outcrossing are found to be alternative stable states of the mating system in most plant populations. Which of these stable states a species approaches depends on the history of its population structure and the magnitude of effect of genes influencing the selfing rate.
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Affiliation(s)
- Russell Lande
- Department of Biology, University of Chicago, Chicago, IL, 60637
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26
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Bull JJ, Pease CM. COMBINATORICS AND VARIETY OF MATING-TYPE SYSTEMS. Evolution 2017; 43:667-671. [DOI: 10.1111/j.1558-5646.1989.tb04263.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/1988] [Accepted: 12/07/1988] [Indexed: 12/01/2022]
Affiliation(s)
- J. J. Bull
- Department of Zoology; University of Texas; Austin TX 78712
| | - Craig M. Pease
- Department of Zoology; University of Texas; Austin TX 78712
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27
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Fry JD, Rausher MD. SELECTION ON A FLORAL COLOR POLYMORPHISM IN THE TALL MORNING GLORY (IPOMOEA PURPUREA): TRANSMISSION SUCCESS OF THE ALLELES THROUGH POLLEN. Evolution 2017; 51:66-78. [PMID: 28568811 DOI: 10.1111/j.1558-5646.1997.tb02389.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/1995] [Accepted: 07/03/1996] [Indexed: 11/30/2022]
Abstract
The W locus, a codominant locus influencing floral pigment intensity in the tall morning glory, Ipomoea purpurea, is polymorphic throughout the southeastern United States. Previous studies suggest that this polymorphism is actively maintained by balancing selection, and that increased selfing accompanied by lack of pollen discounting ("Fisher effect") may act to protect the white allele when it is rare. Processes that act to protect the dark allele and thus stabilize the polymorphism in conjunction with the Fisher effect have not been previously detected. The goal of this study was to determine whether any of three such processes might operate in I. purpurea. Estimates of breeding system parameters in a large experimental population in which the white allele was in higher than normal frequency (0.5) provided little evidence that either dark- or light-flowered plants were more successful as pollen parents than white-flowered plants. In addition, no evidence was found for a transmission bias favoring the dark allele in the ovules produced by light heterozygotes. In contrast, a strong transmission bias favoring the dark allele in pollen of heterozygotes was observed. A simple model using parameter estimates derived from this and previous studies indicates that a balance between the Fisher effect and biased transmission in heterozygote pollen could account for many properties of the polymorphism.
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Affiliation(s)
- James D Fry
- Department of Zoology, Box 90325, Duke University, Durham, North Carolina, 27708-0325
| | - Mark D Rausher
- Department of Zoology, Box 90325, Duke University, Durham, North Carolina, 27708-0325
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28
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Manasse RS, Pinney K. LIMITS TO REPRODUCTIVE SUCCESS IN A PARTIALLY SELF‐INCOMPATIBLE HERB: FECUNDITY DEPRESSION AT SERIAL LIFE‐CYCLE STAGES. Evolution 2017; 45:712-720. [DOI: 10.1111/j.1558-5646.1991.tb04340.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/1989] [Accepted: 06/27/1990] [Indexed: 11/28/2022]
Affiliation(s)
- Robin S. Manasse
- Department of Botany University of California Davis CA 95616 USA
| | - Katherine Pinney
- Department of Pomology University of California Davis CA 95616 USA
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29
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Ritland K. INFERENCES ABOUT INBREEDING DEPRESSION BASED ON CHANGES OF THE INBREEDING COEFFICIENT. Evolution 2017; 44:1230-1241. [PMID: 28563887 DOI: 10.1111/j.1558-5646.1990.tb05227.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/1989] [Accepted: 12/21/1989] [Indexed: 12/01/2022]
Abstract
In a mixed-mating population, the fitness of selfed individuals, relative to outcrossed individuals, can be estimated from observed changes of the inbreeding coefficient F. In general, three measurements of F, or two measurements of F and one of the selfing rate, spanning two generations are needed. If however, adult F is assumed constant among generations, the adult F and selfing rate of one generation are sufficient to estimate relative fitness. Estimates of the relative fitness of selfed individuals for 14 Mimulus populations, assuming equilibrium of adult F, averaged 0.38, which is significantly lower than the 0.50 threshold needed to favor selfing genotypes. However, estimates for some populations showed large variance and over the 14 populations, relative fitness did not correlate with selfing rate. Violations of the equilibrium assumption causes a positive bias of the estimate and a spurious negative correlation of estimates with selfing rate. Estimates of relative fitness based on two generations of F do not suffer these problems. The need for large sample sizes, multiallelic loci, and moderate levels of natural selfing limits the usefulness of using changes of F to infer inbreeding depression.
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Affiliation(s)
- Kermit Ritland
- Department of Botany, University of Toronto, Toronto, M5S3B2, CANADA
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30
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Saumitou-Laprade P, Vernet P, Vekemans X, Billiard S, Gallina S, Essalouh L, Mhaïs A, Moukhli A, El Bakkali A, Barcaccia G, Alagna F, Mariotti R, Cultrera NGM, Pandolfi S, Rossi M, Khadari B, Baldoni L. Elucidation of the genetic architecture of self-incompatibility in olive: Evolutionary consequences and perspectives for orchard management. Evol Appl 2017; 10:867-880. [PMID: 29151878 PMCID: PMC5680433 DOI: 10.1111/eva.12457] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Accepted: 01/05/2017] [Indexed: 12/15/2022] Open
Abstract
The olive (Olea europaea L.) is a typical important perennial crop species for which the genetic determination and even functionality of self‐incompatibility (SI) are still largely unresolved. It is still not known whether SI is under gametophytic or sporophytic genetic control, yet fruit production in orchards depends critically on successful ovule fertilization. We studied the genetic determination of SI in olive in light of recent discoveries in other genera of the Oleaceae family. Using intra‐ and interspecific stigma tests on 89 genotypes representative of species‐wide olive diversity and the compatibility/incompatibility reactions of progeny plants from controlled crosses, we confirmed that O. europaea shares the same homomorphic diallelic self‐incompatibility (DSI) system as the one recently identified in Phillyrea angustifolia and Fraxinus ornus. SI is sporophytic in olive. The incompatibility response differs between the two SI groups in terms of how far pollen tubes grow before growth is arrested within stigma tissues. As a consequence of this DSI system, the chance of cross‐incompatibility between pairs of varieties in an orchard is high (50%) and fruit production may be limited by the availability of compatible pollen. The discovery of the DSI system in O. europaea will undoubtedly offer opportunities to optimize fruit production.
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Affiliation(s)
- Pierre Saumitou-Laprade
- CNRSUMR 8198 Evo-Eco-Paleo Université de Lille - Sciences et Technologies Villeneuve d'Ascq France
| | - Philippe Vernet
- CNRSUMR 8198 Evo-Eco-Paleo Université de Lille - Sciences et Technologies Villeneuve d'Ascq France
| | - Xavier Vekemans
- CNRSUMR 8198 Evo-Eco-Paleo Université de Lille - Sciences et Technologies Villeneuve d'Ascq France
| | - Sylvain Billiard
- CNRSUMR 8198 Evo-Eco-Paleo Université de Lille - Sciences et Technologies Villeneuve d'Ascq France
| | - Sophie Gallina
- CNRSUMR 8198 Evo-Eco-Paleo Université de Lille - Sciences et Technologies Villeneuve d'Ascq France
| | | | - Ali Mhaïs
- Montpellier SupAgro UMR 1334 AGAP Montpellier France.,INRAUR Amélioration des Plantes Marrakech Morocco.,Laboratoire AgroBiotech L02B005 Faculté des Sciences et Techniques Guéliz University Cadi Ayyad Marrakech Morocco
| | | | - Ahmed El Bakkali
- INRAUR Amélioration des Plantes et Conservation des Ressources Phytogénétiques Meknès Morocco
| | - Gianni Barcaccia
- Laboratory of Genomics and Plant Breeding DAFNAE - University of Padova Legnaro PD Italy
| | - Fiammetta Alagna
- Research Unit for Table Grapes and Wine Growing in Mediterranean Environment CREATuriBA Italy.,CNRInstitute of Biosciences and BioresourcesPerugiaItaly
| | | | | | | | - Martina Rossi
- CNRInstitute of Biosciences and BioresourcesPerugiaItaly
| | - Bouchaïb Khadari
- Montpellier SupAgro UMR 1334 AGAP Montpellier France.,INRA/CBNMed UMR 1334 Amélioration Génétique et Adaptation des Plantes (AGAP) Montpellier France
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31
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Layman NC, Fernando MTR, Herlihy CR, Busch JW. Costs of selfing prevent the spread of a self‐compatibility mutation that causes reproductive assurance. Evolution 2017; 71:884-897. [DOI: 10.1111/evo.13167] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Revised: 11/15/2016] [Accepted: 12/21/2016] [Indexed: 02/02/2023]
Affiliation(s)
- Nathan C. Layman
- School of Biological Sciences Washington State University Pullman Washington 99164
| | - M. Thilina R. Fernando
- Department of Biology, Evolution and Ecology Group Middle Tennessee State University Murfreesboro Tennessee 37132
| | - Christopher R. Herlihy
- Department of Biology, Evolution and Ecology Group Middle Tennessee State University Murfreesboro Tennessee 37132
| | - Jeremiah W. Busch
- School of Biological Sciences Washington State University Pullman Washington 99164
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32
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Vernet P, Lepercq P, Billiard S, Bourceaux A, Lepart J, Dommée B, Saumitou-Laprade P. Evidence for the long-term maintenance of a rare self-incompatibility system in Oleaceae. THE NEW PHYTOLOGIST 2016; 210:1408-17. [PMID: 26833140 DOI: 10.1111/nph.13872] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 12/17/2015] [Indexed: 05/21/2023]
Abstract
A rare homomorphic diallelic self-incompatibility (DSI) system discovered in Phillyrea angustifolia (family Oleaceae, subtribe Oleinae) can promote the transition from hermaphroditism to androdioecy. If widespread and stable in Oleaceae, DSI may explain the exceptionally high rate of androdioecious species reported in this plant family. Here, we set out to determine whether DSI occurs in another Oleaceae lineage. We tested for DSI in subtribe Fraxininae, a lineage that diverged from subtribe Oleinae c. 40 million yr ago. We explored the compatibility relationships in Fraxinus ornus using 81 hermaphrodites and 25 males from one natural stand and two naturalized populations using intra- and interspecific stigma tests performed on F. ornus and P. angustifolia testers. We uncovered a DSI system with hermaphrodites belonging to one of two self-incompatibility (SI) groups and males compatible with both groups, making for a truly androdioecious reproductive system. The two human-founded populations contained only one of the two SI groups. Our results provide evidence for the evolutionary persistence of DSI. We discuss how its stability over time may have affected transitions to other sexual systems, such as dioecy.
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Affiliation(s)
- Philippe Vernet
- Université de Lille - Sciences et Technologies, CNRS, UMR 8198 Evo-Eco-Paleo, F59655, Villeneuve d'Ascq, France
| | - Pierre Lepercq
- Université de Lille - Sciences et Technologies, CNRS, UMR 8198 Evo-Eco-Paleo, F59655, Villeneuve d'Ascq, France
| | - Sylvain Billiard
- Université de Lille - Sciences et Technologies, CNRS, UMR 8198 Evo-Eco-Paleo, F59655, Villeneuve d'Ascq, France
| | - Angélique Bourceaux
- Université de Lille - Sciences et Technologies, CNRS, UMR 8198 Evo-Eco-Paleo, F59655, Villeneuve d'Ascq, France
| | - Jacques Lepart
- CEFE-UMR 5175 du CNRS, 1919 route de Mende, 34293, Montpellier Cedex, France
| | - Bertrand Dommée
- CEFE-UMR 5175 du CNRS, 1919 route de Mende, 34293, Montpellier Cedex, France
| | - Pierre Saumitou-Laprade
- Université de Lille - Sciences et Technologies, CNRS, UMR 8198 Evo-Eco-Paleo, F59655, Villeneuve d'Ascq, France
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33
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Schoen DJ, Roda MJ. Selection of sporophytic and gametophytic self-incompatibility in the absence of a superlocus. Evolution 2016; 70:1409-17. [PMID: 27111063 DOI: 10.1111/evo.12930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 04/12/2016] [Accepted: 04/15/2016] [Indexed: 11/30/2022]
Abstract
Self-incompatibility (SI) is a complex trait that enforces outcrossing in plant populations. SI generally involves tight linkage of genes coding for the proteins that underlie self-pollen detection and pollen identity specification. Here, we develop two-locus genetic models to address the question of whether sporophytic SI (SSI) and gametophytic SI (GSI) can invade populations of self-compatible plants when there is no linkage or weak linkage of the underlying pollen detection and identity genes (i.e., no S-locus supergene). The models assume that SI evolves as a result of exaptation of genes formerly involved in functions other than SI. Model analysis reveals that SSI and GSI can invade populations even when the underlying genes are loosely linked, provided that inbreeding depression and selfing rate are sufficiently high. Reducing recombination between these genes makes conditions for invasion more lenient. These results can help account for multiple, independent evolution of SI systems as seems to have occurred in the angiosperms.
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Affiliation(s)
- Daniel J Schoen
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada.
| | - Megan J Roda
- Department of Biology, McGill University, Montreal, Quebec, H3A 1B1, Canada
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34
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Pinheiro F, Cafasso D, Cozzolino S, Scopece G. Transitions between self-compatibility and self-incompatibility and the evolution of reproductive isolation in the large and diverse tropical genus Dendrobium (Orchidaceae). ANNALS OF BOTANY 2015; 116:457-67. [PMID: 25953040 PMCID: PMC4549954 DOI: 10.1093/aob/mcv057] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 03/30/2015] [Indexed: 05/09/2023]
Abstract
BACKGROUND AND AIMS The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus. METHODS The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank. KEY RESULTS Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids. CONCLUSIONS Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.
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Affiliation(s)
- Fabio Pinheiro
- Departamento de Botânica, Instituto de Biociências, Universidade Estadual Paulista, 13506-900, Rio Claro, SP, Brazil,
| | - Donata Cafasso
- Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and
| | - Salvatore Cozzolino
- Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and
| | - Giovanni Scopece
- Università degli Studi di Napoli Federico II, Department of Biology, via Cinthia, I-80126, Naples, Italy and Institute for Plant Protection, Consiglio Nazionale delle Ricerche, Via Madonna del Piano, 10, I-50019, Sesto Fiorentino (FI), Italy
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35
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Hadjivasiliou Z, Iwasa Y, Pomiankowski A. Cell-cell signalling in sexual chemotaxis: a basis for gametic differentiation, mating types and sexes. J R Soc Interface 2015; 12:20150342. [PMID: 26156301 PMCID: PMC4535405 DOI: 10.1098/rsif.2015.0342] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 06/16/2015] [Indexed: 11/29/2022] Open
Abstract
While sex requires two parents, there is no obvious need for them to be differentiated into distinct mating types or sexes. Yet this is the predominate state of nature. Here, we argue that mating types could play a decisive role because they prevent the apparent inevitability of self-stimulation during sexual signalling. We rigorously assess this hypothesis by developing a model for signaller-detector dynamics based on chemical diffusion, chemotaxis and cell movement. Our model examines the conditions under which chemotaxis improves partner finding. Varying parameter values within ranges typical of protists and their environments, we show that simultaneous secretion and detection of a single chemoattractant can cause a multifold movement impediment and severely hinder mate finding. Mutually exclusive roles result in faster pair formation, even when cells conferring the same roles cannot pair up. This arrangement also allows the separate mating types to optimize their signalling or detecting roles, which is effectively impossible for cells that are both secretors and detectors. Our findings suggest that asymmetric roles in sexual chemotaxis (and possibly other forms of sexual signalling) are crucial, even without morphological differences, and may underlie the evolution of gametic differentiation among both mating types and sexes.
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Affiliation(s)
- Zena Hadjivasiliou
- Centre for Mathematics, Physics and Engineering in the Life Sciences and Experimental Biology (CoMPLEX), University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK
| | - Yoh Iwasa
- Department of Biology, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan
| | - Andrew Pomiankowski
- Centre for Mathematics, Physics and Engineering in the Life Sciences and Experimental Biology (CoMPLEX), University College London, Gower Street, London WC1E 6BT, UK Department of Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK
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36
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Van de Paer C, Saumitou-Laprade P, Vernet P, Billiard S. The joint evolution and maintenance of self-incompatibility with gynodioecy or androdioecy. J Theor Biol 2015; 371:90-101. [PMID: 25681148 DOI: 10.1016/j.jtbi.2015.02.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 01/28/2015] [Accepted: 02/02/2015] [Indexed: 10/24/2022]
Abstract
Mating systems show two kinds of frequent transitions: from hermaphroditism to dioecy, gynodioecy or androdioecy, or from self-incompatibility (SI) to self-compatibility (SC). While models have mostly investigated these two kinds of transitions as independent, empirical observations suggest that, to some extent, they can evolve jointly. Here, we study the joint evolution and maintenance of SI and androdioecy or SI and gynodioecy by the means of phenotypic models. Our models focus on three parameters: the unisexuals׳ advantage relative to that of the hermaphrodites due to resource reallocation, inbreeding depression and the selfing rate. We assume no pollen limitation or discounting. We show that SI helps the maintenance of androdioecy, but favors the loss of gynodioecy, and also that androdioecy facilitates the maintenance of SI, whereas gynodioecy does not affect it. We finally investigate how gynodioecy and androdioecy may affect the diversification of SI groups, especially considering an evolutionary pathway through SC intermediates. We show that while androdioecy prevents the increase of the number of SI groups, under certain conditions of inbreeding depression and selfing rates, gynodioecy allows it.
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Affiliation(s)
- Céline Van de Paer
- Unité (EEP), Université des Sciences et Technologies Lille 1, Cité scientifique, 59655 Villeneuve d׳Ascq Cedex, France.
| | - Pierre Saumitou-Laprade
- Unité (EEP), Université des Sciences et Technologies Lille 1, Cité scientifique, 59655 Villeneuve d׳Ascq Cedex, France.
| | - Philippe Vernet
- Unité (EEP), Université des Sciences et Technologies Lille 1, Cité scientifique, 59655 Villeneuve d׳Ascq Cedex, France.
| | - Sylvain Billiard
- Unité (EEP), Université des Sciences et Technologies Lille 1, Cité scientifique, 59655 Villeneuve d׳Ascq Cedex, France.
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37
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Koenig D, Weigel D. Beyond the thale: comparative genomics and genetics of Arabidopsis relatives. Nat Rev Genet 2015; 16:285-98. [DOI: 10.1038/nrg3883] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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38
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Gervais C, Awad DA, Roze D, Castric V, Billiard S. GENETIC ARCHITECTURE OF INBREEDING DEPRESSION AND THE MAINTENANCE OF GAMETOPHYTIC SELF-INCOMPATIBILITY. Evolution 2014; 68:3317-24. [DOI: 10.1111/evo.12495] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Accepted: 07/02/2014] [Indexed: 11/28/2022]
Affiliation(s)
- Camille Gervais
- UMI 3614; Evolutionary Biology and Ecology of Algae; CNRS; 29680 Roscoff France
- Sorbonne Universités; UPMC University Paris 06 29680 Roscoff France
| | - Diala Abu Awad
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
| | - Denis Roze
- UMI 3614; Evolutionary Biology and Ecology of Algae; CNRS; 29680 Roscoff France
- Sorbonne Universités; UPMC University Paris 06 29680 Roscoff France
| | - Vincent Castric
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
| | - Sylvain Billiard
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
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39
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Sakai S, Wakoh H. Initial invasion of gametophytic self-incompatibility alleles in the absence of tight linkage between pollen and pistil S alleles. Am Nat 2014; 184:248-57. [PMID: 25058284 DOI: 10.1086/676942] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
In homomorphic self-incompatibility (SI) systems of plants, the loci controlling the pollen and pistil types are tightly linked, and this prevents the generation of compatible combinations of alleles expressing pollen and pistil types, which would result in self-fertilization. We modeled the initial invasion of the first pollen and pistil alleles in gametophytic SI to determine whether these alleles can stably coexist in a population without tight linkage. We assume pollen and pistil loci each carry an incompatibility allele S and an allele without an incompatibility function N. We assume that pollen with an S allele are incompatible with pistils carrying S alleles, whereas other crosses are compatible. Ovules in pistils carrying an S allele suffer viability costs because recognition consumes resources. We found that the cost of carrying a pistil S allele allows pollen and pistil S alleles to coexist in a stable equilibrium if linkage is partial. This occurs because parents that carry pistil S alleles but are homozygous for pollen N alleles cannot avoid self-fertilization; however, they suffer viability costs. Hence, pollen N alleles are selected again. When pollen and pistil S alleles can coexist in a polymorphic equilibrium, selection will favor tighter linkage.
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Affiliation(s)
- Satoki Sakai
- Department of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University Aoba, Sendai 980-8578, Japan
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40
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Vosters SL, Jewell CP, Sherman NA, Einterz F, Blackman BK, Moyle LC. The timing of molecular and morphological changes underlying reproductive transitions in wild tomatoes (Solanum sect. Lycopersicon). Mol Ecol 2014; 23:1965-78. [PMID: 24589309 DOI: 10.1111/mec.12708] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Revised: 02/01/2014] [Accepted: 02/04/2014] [Indexed: 01/08/2023]
Abstract
Molecular mechanisms underlying the transition from genetic self-incompatibility to self-compatibility are well documented, but the evolution of other reproductive trait changes that accompany shifts in reproductive strategy (mating system) remains comparatively under-investigated. A notable exception is the transition from exserted styles to styles with recessed positions relative to the anthers in wild tomatoes (Solanum Section Lycopersicon). This phenotypic change has been previously attributed to a specific mutation in the promoter of a gene that influences style length (style2.1); however, whether this specific regulatory mutation arose concurrently with the transition from long to short styles, and whether it is causally responsible for this phenotypic transition, has been poorly investigated across this group. To address this gap, we assessed 74 accessions (populations) from 13 species for quantitative genetic variation in floral and reproductive traits as well as the presence/absence of deletions at two different locations (StyleD1 and StyleD2) within the regulatory region upstream of style2.1. We confirmed that the putatively causal deletion variant (a 450-bp deletion at StyleD1) arose within self-compatible lineages. However, the variation and history of both StyleD1 and StyleD2 was more complex than previously inferred. In particular, although StyleD1 was statistically associated with differences in style length and stigma exsertion across all species, we found no evidence for this association within two species polymorphic for the StyleD1 mutation. We conclude that the previous association detected between phenotypic and molecular differences is most likely due to a phylogenetic association rather than a causal mechanistic relationship. Phenotypic variation in style length must therefore be due to other unexamined linked variants in the style2.1 regulatory region.
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Affiliation(s)
- S L Vosters
- Department of Biology, Indiana University, Bloomington, 47405, IN, USA
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41
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Castric V, Billiard S, Vekemans X. Trait transitions in explicit ecological and genomic contexts: plant mating systems as case studies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 781:7-36. [PMID: 24277293 DOI: 10.1007/978-94-007-7347-9_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Abstract
Plants are astonishingly diverse in how they reproduce sexually, and the study of plant mating systems provides some of the most compelling cases of parallel and independent evolutionary transitions. In this chapter, we review how the massive amount of genomic data being produced is allowing long-standing predictions from ecological and evolutionary theory to be put to test. After a review of theoretical predictions about the importance of considering the genomic architecture of the mating system, we focus on a set of recent discoveries on how the mating system is controlled in a variety of model and non-model species. In parallel, genomic approaches have revealed the complex interaction between the evolution of genes controlling mating systems and genome evolution, both genome-wide and in the mating system control region. In several cases, major transitions in the mating system can be clearly associated with important ecological changes, hence illuminating an important interplay between ecological and genomic approaches. We also list a number of major unsolved questions that remain for the field, and highlight foreseeable conceptual developments that are likely to play a major role in our understanding of how plant mating systems evolve in Nature.
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Affiliation(s)
- Vincent Castric
- Laboratoire de Génétique et Evolution des Populations Végétales (GEPV), UMR 8198; CNRS, Université Lille 1, Sciences et Technologies, Cité Scientifique, Villeneuve d'Ascq, France,
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42
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Griffin PC, Willi Y. Evolutionary shifts to self-fertilisation restricted to geographic range margins in North American Arabidopsis lyrata. Ecol Lett 2014; 17:484-90. [PMID: 24428521 DOI: 10.1111/ele.12248] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 11/26/2013] [Accepted: 12/20/2013] [Indexed: 01/08/2023]
Abstract
Cross-fertilisation predominates in eukaryotes, but shifts to self-fertilisation are common and ecologically and evolutionarily important. Reproductive assurance under outcross gamete limitation is one eco-evolutionary process held responsible for the shift to selfing. Although small effective population size is a situation where selfing plants could theoretically benefit from reproductive assurance, empirical tests of the role of population size are rare. Here, we show that selfing evolved repeatedly at range margins, where historical demographic processes produced low effective population sizes. Outcrossing populations of North American Arabidopsis lyrata have low genetic diversity at geographic margins, with a signature of post-glacial range expansion in the north and rear-edge isolation in the south. Selfing populations occur at the margins of two genetic groups and never in their interior. These results corroborate small effective population size as the promoter of self-fertilisation and have important implications for our understanding of species turnover, range limits and range dynamics.
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Affiliation(s)
- P C Griffin
- Evolutionary Botany, Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, CH-2000, Neuchâtel, Switzerland
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43
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Tsuchimatsu T, Shimizu KK. Effects of pollen availability and the mutation bias on the fixation of mutations disabling the male specificity of self-incompatibility. J Evol Biol 2013; 26:2221-32. [PMID: 23980527 DOI: 10.1111/jeb.12219] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Revised: 06/21/2013] [Accepted: 06/24/2013] [Indexed: 01/19/2023]
Abstract
The evolution of self-compatibility (SC) by the loss of self-incompatibility (SI) is regarded as one of the most frequent transitions in flowering plants. SI systems are generally characterized by specific interactions between the male and female specificity genes encoded at the S-locus. Recent empirical studies have revealed that the evolution of SC is often driven by male SC-conferring mutations at the S-locus rather than by female mutations. In this study, using a forward simulation model, we compared the fixation probabilities of male vs. female SC-conferring mutations at the S-locus. We explicitly considered the effects of pollen availability in the population and bias in the occurrence of SC-conferring mutations on the male and female specificity genes. We found that male SC-conferring mutations were indeed more likely to be fixed than were female SC-conferring mutations in a wide range of parameters. This pattern was particularly strong when pollen availability was relatively high. Under such a condition, even if the occurrence of mutations was biased strongly towards the female specificity gene, male SC-conferring mutations were much more often fixed. Our study demonstrates that fixation probabilities of those two types of mutation vary strongly depending on ecological and genetic conditions, although both types result in the same evolutionary consequence-the loss of SI.
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Affiliation(s)
- T Tsuchimatsu
- Institute of Evolutionary Biology and Environmental Studies, Institute of Plant Biology & Zurich-Basel Plant Science Center, University of Zurich, Zurich, Switzerland; Gregor Mendel Institute, Austrian Academy of Sciences, Vienna, Austria
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Tsuchimatsu T, Kaiser P, Yew CL, Bachelier JB, Shimizu KK. Recent loss of self-incompatibility by degradation of the male component in allotetraploid Arabidopsis kamchatica. PLoS Genet 2012; 8:e1002838. [PMID: 22844253 PMCID: PMC3405996 DOI: 10.1371/journal.pgen.1002838] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 06/04/2012] [Indexed: 01/01/2023] Open
Abstract
The evolutionary transition from outcrossing to self-fertilization (selfing) through the loss of self-incompatibility (SI) is one of the most prevalent events in flowering plants, and its genetic basis has been a major focus in evolutionary biology. In the Brassicaceae, the SI system consists of male and female specificity genes at the S-locus and of genes involved in the female downstream signaling pathway. During recent decades, much attention has been paid in particular to clarifying the genes responsible for the loss of SI. Here, we investigated the pattern of polymorphism and functionality of the female specificity gene, the S-locus receptor kinase (SRK), in allotetraploid Arabidopsis kamchatica. While its parental species, A. lyrata and A. halleri, are reported to be diploid and mainly self-incompatible, A. kamchatica is self-compatible. We identified five highly diverged SRK haplogroups, found their disomic inheritance and, for the first time in a wild allotetraploid species, surveyed the geographic distribution of SRK at the two homeologous S-loci across the species range. We found intact full-length SRK sequences in many accessions. Through interspecific crosses with the self-incompatible and diploid congener A. halleri, we found that the female components of the SI system, including SRK and the female downstream signaling pathway, are still functional in these accessions. Given the tight linkage and very rare recombination of the male and female components on the S-locus, this result suggests that the degradation of male components was responsible for the loss of SI in A. kamchatica. Recent extensive studies in multiple Brassicaceae species demonstrate that the loss of SI is often derived from mutations in the male component in wild populations, in contrast to cultivated populations. This is consistent with theoretical predictions that mutations disabling male specificity are expected to be more strongly selected than mutations disabling female specificity, or the female downstream signaling pathway.
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Affiliation(s)
| | | | | | | | - Kentaro K. Shimizu
- Institute of Evolutionary Biology and Environmental Studies, Institute of Plant Biology, and Zurich-Basel Plant Science Center, University of Zurich, Zurich, Switzerland
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Li J, Webster MA, Smith MC, Gilmartin PM. Floral heteromorphy in Primula vulgaris: progress towards isolation and characterization of the S locus. ANNALS OF BOTANY 2011; 108:715-726. [PMID: 21803742 PMCID: PMC3170159 DOI: 10.1093/aob/mcr181] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 05/16/2011] [Indexed: 05/27/2023]
Abstract
BACKGROUND The common primrose, Primula vulgaris, along with many other species of the Primulaceae, exhibits floral heteromorphy in which different individuals develop one of two possible forms of flower, known as pin and thrum. Both flower types are hermaphrodite and exhibit reciprocal positions of male and female reproductive structures, which together with a sporophytic incompatibility system, prevent self-pollination and promote out-crossing. The development of the two different forms of flower is controlled by a co-adapted linkage group of genes known as the S locus. SCOPE Here progress towards identification and characterization of these genes is described to provide a molecular genetic explanation of the different floral characteristics that define heterostyly in Primula as observed and described by Charles Darwin. Previous work to identify and characterize developmental mutations linked to the P. vulgaris S locus, together with the isolation of S locus-linked genes and polymorphic DNA sequences markers, is summarized. The development of tools are described which will facilitate isolation and characterization of the S locus and its environs, including the creation of two expressed sequence tag libraries from pin and thrum flowers, as well as the construction and screening of two bacterial artificial chromosome (BAC) libraries containing thrum genomic DNA. Screening of these libraries with four S locus-linked sequences has enabled us to assemble four BAC contigs representing over 40 individual overlapping BAC clones which represent over 2·2 Mb of S locus-linked genomic sequence. PCR-based approaches for identification of the allelic origin of these BACs are described as well as identification of an additional 14 S locus-linked genes within BAC-end sequences. CONCLUSIONS On-going work to assemble the four S locus-linked contigs into one contiguous sequence spanning the S locus is outlined in preparation for sequence analysis and characterization of the genes located within this region.
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Abstract
Self-incompatibility (SI) is a genetic system found in some hermaphrodite plants. Recognition of pollen by pistils expressing cognate specificities at two linked genes leads to rejection of self pollen and pollen from close relatives, i.e., to avoidance of self-fertilization and inbred matings, and thus increased outcrossing. These genes generally have many alleles, yet the conditions allowing the evolution of new alleles remain mysterious. Evolutionary changes are clearly necessary in both genes, since any mutation affecting only one of them would result in a nonfunctional self-compatible haplotype. Here, we study diversification at the S-locus (i.e., a stable increase in the total number of SI haplotypes in the population, through the incorporation of new SI haplotypes), both deterministically (by investigating analytically the fate of mutations in an infinite population) and by simulations of finite populations. We show that the conditions allowing diversification are far less stringent in finite populations with recurrent mutations of the pollen and pistil genes, suggesting that diversification is possible in a panmictic population. We find that new SI haplotypes emerge fastest in populations with few SI haplotypes, and we discuss some implications for empirical data on S-alleles. However, allele numbers in our simulations never reach values as high as observed in plants whose SI systems have been studied, and we suggest extensions of our models that may reconcile the theory and data.
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Billiard S, López-Villavicencio M, Devier B, Hood ME, Fairhead C, Giraud T. Having sex, yes, but with whom? Inferences from fungi on the evolution of anisogamy and mating types. Biol Rev Camb Philos Soc 2010; 86:421-42. [PMID: 21489122 DOI: 10.1111/j.1469-185x.2010.00153.x] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The advantage of sex has been among the most debated issues in biology. Surprisingly, the question of why sexual reproduction generally requires the combination of distinct gamete classes, such as small and large gametes, or gametes with different mating types, has been much less investigated. Why do systems with alternative gamete classes (i.e. systems with either anisogamy or mating types or both) appear even though they restrict the probability of finding a compatible mating partner? Why does the number of gamete classes vary from zero to thousands, with most often only two classes? We review here the hypotheses proposed to explain the origin, maintenance, number, and loss of gamete classes. We argue that fungi represent highly suitable models to help resolve issues related to the evolution of distinct gamete classes, because the number of mating types vary from zero to thousands across taxa, anisogamy is present or not, and because there are frequent transitions between these conditions. We review the nature and number of gamete classes in fungi, and we attempt to draw inferences from these data on the evolutionary forces responsible for their appearance, loss or maintenance, and number.
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Affiliation(s)
- Sylvain Billiard
- Université Lille Nord de France, USTL, GEPV, CNRS, FRE 3268, Villeneuve d'Ascq, France.
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Busch JW, Herlihy CR, Gunn L, Werner WJ. Mixed mating in a recently derived self-compatible population of Leavenworthia alabamica (Brassicaceae). AMERICAN JOURNAL OF BOTANY 2010; 97:1005-1013. [PMID: 21622470 DOI: 10.3732/ajb.1000032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
PREMISE OF THE STUDY A mixture of outcrossing and selfing is often observed in plant populations. Although mixed mating is ubiquitous, it has several potential evolutionary explanations. Mixed mating may be actively maintained by selection, passively determined by the pollination environment, or a transitional stage during the evolution of self-fertilization. • METHODS We studied patterns of self-compatibility and selfing rates in a population of Leavenworthia alabamica that recently lost self-incompatibility. We also experimentally tested whether natural selection against selfing at the pre- or postzygotic stage is sufficient to explain mixed mating in this population. • KEY RESULTS Visualizing pollen tube growth following self-pollination, we found that nearly all plants were fully self-compatible. Progeny array analysis revealed that the average selfing rate of the population was s = 0.523. The inbreeding coefficient in the parents (F = 0.539) exceeded the amount expected if the selfing rate (s) were constant [F(eq) = s/(2 - s)], indicating either population subdivision or higher selfing rates in the past. Inference of family-level selfing rates revealed substantial variation. Experiments found that self and outcross pollen fertilized nearly equal numbers of ovules in competition. Comparison of seed production following self- or cross-pollination failed to implicate early acting inbreeding depression as a factor maintaining mixed mating. • CONCLUSIONS The results of our experiments suggest that mixed mating is not maintained by selection against self-pollen or zygotes in this population. Mixed mating is most likely a byproduct of the pollination process but may also be a transitional stage during the evolution of higher selfing rates.
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Affiliation(s)
- Jeremiah W Busch
- School of Biological Sciences and the Center for Reproductive Biology, Washington State University, P.O. Box 644236, Pullman, Washington 99164 USA
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Busch JW, Joly S, Schoen DJ. DOES MATE LIMITATION IN SELF-INCOMPATIBLE SPECIES PROMOTE THE EVOLUTION OF SELFING? THE CASE OF LEAVENWORTHIA ALABAMICA. Evolution 2009; 64:1657-70. [DOI: 10.1111/j.1558-5646.2009.00925.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Genetic diversity and fitness in small populations of partially asexual, self-incompatible plants. Heredity (Edinb) 2009; 104:482-92. [PMID: 19920857 DOI: 10.1038/hdy.2009.159] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
How self-incompatibility systems are maintained in plant populations is still a debated issue. Theoretical models predict that self-incompatibility systems break down according to the intensity of inbreeding depression and number of S-alleles. Other studies have explored the function of asexual reproduction in the maintenance of self-incompatibility. However, the population genetics of partially asexual, self-incompatible populations are poorly understood and previous studies have failed to consider all possible effects of asexual reproduction or could only speculate on those effects. In this study, we investigated how partial asexuality may affect genetic diversity at the S-locus and fitness in small self-incompatible populations. A genetic model including an S-locus and a viability locus was developed to perform forward simulations of the evolution of populations of various sizes. Drift combined with partial asexuality produced a decrease in the number of alleles at the S-locus. In addition, an excess of heterozygotes was present in the population, causing an increase in mutation load. This heterozygote excess was enhanced by the self-incompatibility system in small populations. In addition, in highly asexual populations, individuals produced asexually had some fitness advantages over individuals produced sexually, because sexual reproduction produces homozygotes of the deleterious allele, contrary to asexual reproduction. Our results suggest that future research on the function of asexuality for the maintenance of self-incompatibility will need to (1) account for whole-genome fitness (mutation load generated by asexuality, self-incompatibility and drift) and (2) acknowledge that the maintenance of self-incompatibility may not be independent of the maintenance of sex itself.
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