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Pennell TM, Mank JE, Alonzo SH, Hosken DJ. On the resolution of sexual conflict over shared traits. Proc Biol Sci 2024; 291:20240438. [PMID: 39082243 PMCID: PMC11289733 DOI: 10.1098/rspb.2024.0438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2023] [Revised: 06/26/2024] [Accepted: 07/05/2024] [Indexed: 08/02/2024] Open
Abstract
Anisogamy, different-sized male and female gametes, sits at the heart of sexual selection and conflict between the sexes. Sperm producers (males) and egg producers (females) of the same species generally share most, if not all, of the same genome, but selection frequently favours different trait values in each sex for traits common to both. The extent to which this conflict might be resolved, and the potential mechanisms by which this can occur, have been widely debated. Here, we summarize recent findings and emphasize that once the sexes evolve, sexual selection is ongoing, and therefore new conflict is always possible. In addition, sexual conflict is largely a multivariate problem, involving trait combinations underpinned by networks of interconnected genes. Although these complexities can hinder conflict resolution, they also provide multiple possible routes to decouple male and female phenotypes and permit sex-specific evolution. Finally, we highlight difficulty in the study of sexual conflict over shared traits and promising directions for future research.
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Affiliation(s)
- Tanya M. Pennell
- Centre for Ecology & Conservation, Faculty of Environment, Science and Economy (ESE), University of Exeter, Cornwall Campus, PenrynTR10 9EZ, UK
| | - Judith E. Mank
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BCV6T 1Z4, Canada
| | - Suzanne H. Alonzo
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA95060, USA
| | - David J. Hosken
- Centre for Ecology & Conservation, Faculty of Environment, Science and Economy (ESE), University of Exeter, Cornwall Campus, PenrynTR10 9EZ, UK
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2
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Singh A, Hasan A, Agrawal AF. An investigation of the sex-specific genetic architecture of fitness in Drosophila melanogaster. Evolution 2023; 77:2015-2028. [PMID: 37329263 DOI: 10.1093/evolut/qpad107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 05/14/2023] [Accepted: 06/13/2023] [Indexed: 06/19/2023]
Abstract
In dioecious populations, the sexes employ divergent reproductive strategies to maximize fitness and, as a result, genetic variants can affect fitness differently in males and females. Moreover, recent studies have highlighted an important role of the mating environment in shaping the strength and direction of sex-specific selection. Here, we measure adult fitness for each sex of 357 lines from the Drosophila Synthetic Population Resource in two different mating environments. We analyze the data using three different approaches to gain insight into the sex-specific genetic architecture for fitness: classical quantitative genetics, genomic associations, and a mutational burden approach. The quantitative genetics analysis finds that on average segregating genetic variation in this population has concordant fitness effects both across the sexes and across mating environments. We do not find specific genomic regions with strong associations with either sexually antagonistic (SA) or sexually concordant (SC) fitness effects, yet there is modest evidence of an excess of genomic regions with weak associations, with both SA and SC fitness effects. Our examination of mutational burden indicates stronger selection against indels and loss-of-function variants in females than in males.
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Affiliation(s)
- Amardeep Singh
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Asad Hasan
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Aneil F Agrawal
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada
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3
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Parrett JM, Łukasiewicz A, Chmielewski S, Szubert-Kruszyńska A, Maurizio PL, Grieshop K, Radwan J. A sexually selected male weapon characterized by strong additive genetic variance and no evidence for sexually antagonistic polyphenic maintenance. Evolution 2023; 77:1289-1302. [PMID: 36848265 PMCID: PMC10234106 DOI: 10.1093/evolut/qpad039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Revised: 12/12/2022] [Accepted: 02/24/2023] [Indexed: 03/01/2023]
Abstract
Sexual selection and sexual antagonism are important drivers of eco-evolutionary processes. The evolution of traits shaped by these processes depends on their genetic architecture, which remains poorly studied. Here, implementing a quantitative genetics approach using diallel crosses of the bulb mite, Rhizoglyphus robini, we investigated the genetic variance that underlies a sexually selected weapon that is dimorphic among males and female fecundity. Previous studies indicated that a negative genetic correlation between these two traits likely exists. We found male morph showed considerable additive genetic variance, which is unlikely to be explained solely by mutation-selection balance, indicating the likely presence of large-effect loci. However, a significant magnitude of inbreeding depression also indicates that morph expression is likely to be condition-dependent to some degree and that deleterious recessives can simultaneously contribute to morph expression. Female fecundity also showed a high degree of inbreeding depression, but the variance in female fecundity was mostly explained by epistatic effects, with very little contribution from additive effects. We found no significant genetic correlation, nor any evidence for dominance reversal, between male morph and female fecundity. The complex genetic architecture underlying male morph and female fecundity in this system has important implications for our understanding of the evolutionary interplay between purifying selection and sexually antagonistic selection.
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Affiliation(s)
- Jonathan M Parrett
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, Poznań, Poland
| | - Aleksandra Łukasiewicz
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, Poznań, Poland
| | - Sebastian Chmielewski
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, Poznań, Poland
| | | | - Paul L Maurizio
- Department of Medicine, Section of Genetic Medicine, University of Chicago, Chicago, Illinois, United States
| | - Karl Grieshop
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Jacek Radwan
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, Poznań, Poland
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Parrett JM, Chmielewski S, Aydogdu E, Łukasiewicz A, Rombauts S, Szubert-Kruszyńska A, Babik W, Konczal M, Radwan J. Genomic evidence that a sexually selected trait captures genome-wide variation and facilitates the purging of genetic load. Nat Ecol Evol 2022; 6:1330-1342. [DOI: 10.1038/s41559-022-01816-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 05/26/2022] [Indexed: 10/17/2022]
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5
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Olito C, Vries CD. The demographic costs of sexually antagonistic selection in partially selfing populations. Am Nat 2022; 200:401-418. [DOI: 10.1086/720419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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6
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Kokko H. The stagnation paradox: the ever-improving but (more or less) stationary population fitness. Proc Biol Sci 2021; 288:20212145. [PMID: 34784767 PMCID: PMC8596016 DOI: 10.1098/rspb.2021.2145] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Fisher's fundamental theorem states that natural selection improves mean fitness. Fitness, in turn, is often equated with population growth. This leads to an absurd prediction that life evolves to ever-faster growth rates, yet no one seriously claims generally slower population growth rates in the Triassic compared with the present day. I review here, using non-technical language, how fitness can improve yet stay constant (stagnation paradox), and why an unambiguous measure of population fitness does not exist. Subfields use different terminology for aspects of the paradox, referring to stasis, cryptic evolution or the difficulty of choosing an appropriate fitness measure; known resolutions likewise use diverse terms from environmental feedback to density dependence and ‘evolutionary environmental deterioration’. The paradox vanishes when these concepts are understood, and adaptation can lead to declining reproductive output of a population when individuals can improve their fitness by exploiting conspecifics. This is particularly readily observable when males participate in a zero-sum game over paternity and population output depends more strongly on female than male fitness. Even so, the jury is still out regarding the effect of sexual conflict on population fitness. Finally, life-history theory and genetic studies of microevolutionary change could pay more attention to each other.
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Affiliation(s)
- Hanna Kokko
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
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7
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Parrett JM, Ghobert V, Cullen FS, Knell RJ. Strong sexual selection fails to protect against inbreeding-driven extinction in a moth. Behav Ecol 2021. [DOI: 10.1093/beheco/arab056] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Sexual selection is predicted to influence population persistence because skew in male reproductive success may facilitate the purging of mutation load. We manipulated the strength of sexual selection in populations of Indian meal moths, Plodia interpunctella, by adjusting adult sex ratios to be either male- or female-biased, leading to strong and weak sexual selection in males, respectively. After between 19 and 22 generations of experimental evolution, we examined whether mutation load differed between these populations by enforcing successive generations of inbreeding, tracking extinction events, offspring viability and assaying the effect of inbreeding on male mating success and female choice. We found no effect of the strength of sexual selection on the rate of extinction or offspring viability. We did, however, find changes in both male mating success and female choice, with both being influenced by the sex ratio treatment and the number of generations of inbreeding. Males from male-biased populations were more successful at mating with stock females, and mating success declined rapidly with inbreeding regardless of sex ratio treatment. Females from male-biased populations were less likely to mate with stock males at the onset of the experiment, but tended to mate more frequently with increasing inbreeding compared to females from female-biased populations. Our results demonstrate that while mating behaviors have diverged between male-biased and female-biased lines mutation loads remained similar. This suggests that the benefits of sexual selection to population fitness may be low or slow to accumulate under the benign environmental conditions in which these populations evolved.
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Affiliation(s)
- Jonathan M Parrett
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
- Evolutionary Biology Group, Faculty of Biology, Adam Mickiewicz University, ul. Uniwersytetu Poznańskiego 6, Poznań, Poland
| | - Veronica Ghobert
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Fenn S Cullen
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
| | - Robert J Knell
- School of Biological and Chemical Sciences, Queen Mary University of London, London, UK
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Grieshop K, Maurizio PL, Arnqvist G, Berger D. Selection in males purges the mutation load on female fitness. Evol Lett 2021; 5:328-343. [PMID: 34367659 PMCID: PMC8327962 DOI: 10.1002/evl3.239] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Revised: 05/05/2021] [Accepted: 05/10/2021] [Indexed: 11/26/2022] Open
Abstract
Theory predicts that the ability of selection and recombination to purge mutation load is enhanced if selection against deleterious genetic variants operates more strongly in males than females. However, direct empirical support for this tenet is limited, in part because traditional quantitative genetic approaches allow dominance and intermediate-frequency polymorphisms to obscure the effects of the many rare and partially recessive deleterious alleles that make up the main part of a population's mutation load. Here, we exposed the partially recessive genetic load of a population of Callosobruchus maculatus seed beetles via successive generations of inbreeding, and quantified its effects by measuring heterosis-the increase in fitness experienced when masking the effects of deleterious alleles by heterozygosity-in a fully factorial sex-specific diallel cross among 16 inbred strains. Competitive lifetime reproductive success (i.e., fitness) was measured in male and female outcrossed F1s as well as inbred parental "selfs," and we estimated the 4 × 4 male-female inbred-outbred genetic covariance matrix for fitness using Bayesian Markov chain Monte Carlo simulations of a custom-made general linear mixed effects model. We found that heterosis estimated independently in males and females was highly genetically correlated among strains, and that heterosis was strongly negatively genetically correlated to outbred male, but not female, fitness. This suggests that genetic variation for fitness in males, but not in females, reflects the amount of (partially) recessive deleterious alleles segregating at mutation-selection balance in this population. The population's mutation load therefore has greater potential to be purged via selection in males. These findings contribute to our understanding of the prevalence of sexual reproduction in nature and the maintenance of genetic variation in fitness-related traits.
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Affiliation(s)
- Karl Grieshop
- Animal Ecology, Department of Ecology and GeneticsUppsala UniversityUppsalaSE‐75236Sweden
- Department of Ecology and Evolutionary BiologyUniversity of TorontoTorontoONM5S 3B2Canada
- Department of Molecular BiosciencesThe Wenner‐Gren InstituteStockholm UniversityStockholmSE‐10691Sweden
| | - Paul L. Maurizio
- Section of Genetic Medicine, Department of MedicineUniversity of ChicagoChicagoIllinois60637
| | - Göran Arnqvist
- Animal Ecology, Department of Ecology and GeneticsUppsala UniversityUppsalaSE‐75236Sweden
| | - David Berger
- Animal Ecology, Department of Ecology and GeneticsUppsala UniversityUppsalaSE‐75236Sweden
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Grieshop K, Arnqvist G. Sex-specific dominance reversal of genetic variation for fitness. PLoS Biol 2018; 16:e2006810. [PMID: 30533008 PMCID: PMC6303075 DOI: 10.1371/journal.pbio.2006810] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 12/21/2018] [Accepted: 11/27/2018] [Indexed: 11/18/2022] Open
Abstract
The maintenance of genetic variance in fitness represents one of the most longstanding enigmas in evolutionary biology. Sexually antagonistic (SA) selection may contribute substantially to maintaining genetic variance in fitness by maintaining alternative alleles with opposite fitness effects in the two sexes. This is especially likely if such SA loci exhibit sex-specific dominance reversal (SSDR)-wherein the allele that benefits a given sex is also dominant in that sex-which would generate balancing selection and maintain stable SA polymorphisms for fitness. However, direct empirical tests of SSDR for fitness are currently lacking. Here, we performed a full diallel cross among isogenic strains derived from a natural population of the seed beetle Callosobruchus maculatus that is known to exhibit SA genetic variance in fitness. We measured sex-specific competitive lifetime reproductive success (i.e., fitness) in >500 sex-by-genotype F1 combinations and found that segregating genetic variation in fitness exhibited pronounced contributions from dominance variance and sex-specific dominance variance. A closer inspection of the nature of dominance variance revealed that the fixed allelic variation captured within each strain tended to be dominant in one sex but recessive in the other, revealing genome-wide SSDR for SA polymorphisms underlying fitness. Our findings suggest that SA balancing selection could play an underappreciated role in maintaining fitness variance in natural populations.
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Affiliation(s)
- Karl Grieshop
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala, Sweden
- * E-mail:
| | - Göran Arnqvist
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala, Sweden
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Grieshop K, Berger D, Arnqvist G. Male-benefit sexually antagonistic genotypes show elevated vulnerability to inbreeding. BMC Evol Biol 2017; 17:134. [PMID: 28606137 PMCID: PMC5469140 DOI: 10.1186/s12862-017-0981-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Accepted: 05/25/2017] [Indexed: 12/26/2022] Open
Abstract
Background There is theoretical and empirical evidence for strong sexual selection in males having positive effects on population viability by serving to purify the genome of its mutation load at a low demographic cost. However, there is also theoretical and empirical evidence for negative effects of sexual selection on female fitness, and therefore population viability, known as the gender load. This can take the form of sexually antagonistic (SA) genetic variation where alleles with a selective advantage in males pose a detriment to female fitness, and vice versa. Here, using seed beetles, we shed light on a previously unexplored manifestation of the gender load: the effect of SA genetic variation on tolerance to inbreeding. Results We found that genotypes encoding high male, but low female fitness exhibited significantly greater rates of extinction upon enforced inbreeding relative to genotypes encoding high female but low male fitness. Also, genotypes encoding low fitness in both sexes exhibited greater rates of extinction relative to generally high-fitness genotypes (though marginally non-significant), an expected finding attributable to variation in mutation load across genotypes. Despite follow-up investigations aiming to identify the mechanism(s) underlying these findings, it remains unclear whether the gender load and the mutation load have independent consequences for tolerance to inbreeding, or whether these two types of genetic architecture interact epistatically to render male-benefit genetic variation relatively intolerant to inbreeding. Conclusions Regardless of the underlying mechanism(s), our results show that male-benefit/female-detriment SA genetic variation poses a previously unseen detriment to population viability due to its elevated vulnerability to inbreeding/homozygosity. This suggests that sexual selection in the context of SA genetic variance for fitness may enhance the gender load on population viability more than previously appreciated, due to selecting for male-benefit SA genetic variation that engenders lineages to extinction upon inbreeding. We note that our results imply that SA alleles that are sexually selected for in males may be underrepresented or even lacking in panels of inbred lines. Electronic supplementary material The online version of this article (doi:10.1186/s12862-017-0981-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Karl Grieshop
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden.
| | - David Berger
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden
| | - Göran Arnqvist
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Norbyvägen 18D, 752 36, Uppsala, Sweden
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