1
|
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.
Collapse
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
| |
Collapse
|
2
|
Olito C, Connallon T. Sexually Antagonistic Variation and the Evolution of Dimorphic Sexual Systems. Am Nat 2019; 193:688-701. [DOI: 10.1086/702847] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
3
|
Pennell TM, Holman L, Morrow EH, Field J. Building a new research framework for social evolution: intralocus caste antagonism. Biol Rev Camb Philos Soc 2018; 93:1251-1268. [PMID: 29341390 PMCID: PMC5896731 DOI: 10.1111/brv.12394] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Revised: 12/06/2017] [Accepted: 12/18/2017] [Indexed: 01/02/2023]
Abstract
The breeding and non‐breeding ‘castes’ of eusocial insects provide a striking example of role‐specific selection, where each caste maximises fitness through different morphological, behavioural and physiological trait values. Typically, queens are long‐lived egg‐layers, while workers are short‐lived, largely sterile foragers. Remarkably, the two castes are nevertheless produced by the same genome. The existence of inter‐caste genetic correlations is a neglected consequence of this shared genome, potentially hindering the evolution of caste dimorphism: alleles that increase the productivity of queens may decrease the productivity of workers and vice versa, such that each caste is prevented from reaching optimal trait values. A likely consequence of this ‘intralocus caste antagonism’ should be the maintenance of genetic variation for fitness and maladaptation within castes (termed ‘caste load’), analogous to the result of intralocus sexual antagonism. The aim of this review is to create a research framework for understanding caste antagonism, drawing in part upon conceptual similarities with sexual antagonism. By reviewing both the social insect and sexual antagonism literature, we highlight the current empirical evidence for caste antagonism, discuss social systems of interest, how antagonism might be resolved, and challenges for future research. We also introduce the idea that sexual and caste antagonism could interact, creating a three‐way antagonism over gene expression. This includes unpacking the implications of haplodiploidy for the outcome of this complex interaction.
Collapse
Affiliation(s)
- Tanya M Pennell
- College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall, TR10 9FE, UK
| | - Luke Holman
- School of Biosciences, University of Melbourne, Parkville, Victoria, 3052, Australia
| | - Edward H Morrow
- Evolution Behaviour and Environment Group, School of Life Sciences, University of Sussex, Falmer, East Sussex, BN1 9QG, UK
| | - Jeremy Field
- College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall, TR10 9FE, UK
| |
Collapse
|
4
|
Affiliation(s)
- Mathieu Douhard
- Département de Biologie; Université de Sherbrooke; 2500 boulevard de l’ Université Sherbrooke QC J1K 2R1 Canada
| |
Collapse
|
5
|
Pischedda A, Chippindale AK. Direct benefits of choosing a high-fitness mate can offset the indirect costs associated with intralocus sexual conflict. Evolution 2017; 71:1710-1718. [PMID: 28369895 DOI: 10.1111/evo.13240] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 03/16/2017] [Indexed: 11/30/2022]
Abstract
Intralocus sexual conflict generates a cost to mate choice: high-fitness partners transmit genetic variation that confers lower fitness to offspring of the opposite sex. Our earlier work in the fruit fly, Drosophila melanogaster, revealed that these indirect genetic costs were sufficient to reverse potential "good genes" benefits of sexual selection. However, mate choice can also confer direct fitness benefits by inducing larger numbers of progeny. Here, we consider whether direct benefits through enhanced fertility could offset the costs associated with intralocus sexual conflict in D. melanogaster. Using hemiclonal analysis, we found that females mated to high-fitness males produced 11% more offspring compared to those mated to low-fitness males, and high-fitness females produced 34% more offspring than low-fitness females. These direct benefits more than offset the reduction in offspring fitness caused by intralocus sexual conflict, creating a net fitness benefit for each sex to pairing with a high-fitness partner. Our findings highlight the need to consider both direct and indirect effects when investigating the fitness impacts of mate choice. Direct fitness benefits may shelter sexually antagonistic alleles from selection, suggesting a novel mechanism for the maintenance of fitness variation.
Collapse
Affiliation(s)
- Alison Pischedda
- Department of Biological Sciences, Mississippi State University, Mississippi, 39762
| | - Adam K Chippindale
- Department of Biology, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| |
Collapse
|
6
|
Douhard M, Festa-Bianchet M, Coltman DW, Pelletier F. Paternal reproductive success drives sex allocation in a wild mammal. Evolution 2016; 70:358-68. [DOI: 10.1111/evo.12860] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 01/10/2016] [Indexed: 01/08/2023]
Affiliation(s)
- Mathieu Douhard
- Département de biologie and Centre d’Études Nordiques; Université de Sherbrooke; 2500 boulevard de l'Université Sherbrooke Québec J1K 2R1 Canada
| | - Marco Festa-Bianchet
- Département de biologie and Centre d’Études Nordiques; Université de Sherbrooke; 2500 boulevard de l'Université Sherbrooke Québec J1K 2R1 Canada
| | - David W. Coltman
- Department of Biological Sciences; University of Alberta; Edmonton Alberta T6G 2E9 Canada
| | - Fanie Pelletier
- Département de biologie and Centre d’Études Nordiques; Université de Sherbrooke; 2500 boulevard de l'Université Sherbrooke Québec J1K 2R1 Canada
| |
Collapse
|
7
|
Booksmythe I, Mautz B, Davis J, Nakagawa S, Jennions MD. Facultative adjustment of the offspring sex ratio and male attractiveness: a systematic review and meta-analysis. Biol Rev Camb Philos Soc 2015; 92:108-134. [DOI: 10.1111/brv.12220] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 08/09/2015] [Accepted: 08/28/2015] [Indexed: 01/12/2023]
Affiliation(s)
- Isobel Booksmythe
- Division of Evolution, Ecology & Genetics; Research School of Biology, The Australian National University; Daley road Canberra Australian Capital Territory 2601 Australia
- Department of Animal Ecology; Evolutionary Biology Centre, Uppsala University; Norbyvägen 18D SE-75236 Uppsala Sweden
- Institute of Evolutionary Biology and Environmental Studies; University of Zürich; Winterthurerstrasse 190 CH-8057 Zürich Switzerland
| | - Brian Mautz
- Division of Evolution, Ecology & Genetics; Research School of Biology, The Australian National University; Daley road Canberra Australian Capital Territory 2601 Australia
- Department of Animal Ecology; Evolutionary Biology Centre, Uppsala University; Norbyvägen 18D SE-75236 Uppsala Sweden
| | - Jacqueline Davis
- Division of Evolution, Ecology & Genetics; Research School of Biology, The Australian National University; Daley road Canberra Australian Capital Territory 2601 Australia
- Department of Psychology; University of Cambridge; Downing Street CB2 3EB Cambridge U.K
| | - Shinichi Nakagawa
- Department of Zoology; University of Otago; PO Box 56 Dunedin 9054 New Zealand
- Evolution & Ecology Research Centre, School of Biological, Earth and Environmental Sciences; University of New South Wales; Sydney New South Wales 2052 Australia
| | - Michael D. Jennions
- Division of Evolution, Ecology & Genetics; Research School of Biology, The Australian National University; Daley road Canberra Australian Capital Territory 2601 Australia
| |
Collapse
|
8
|
Calsbeek R, Duryea MC, Goedert D, Bergeron P, Cox RM. Intralocus sexual conflict, adaptive sex allocation, and the heritability of fitness. J Evol Biol 2015; 28:1975-85. [PMID: 26310599 DOI: 10.1111/jeb.12713] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2014] [Revised: 06/25/2015] [Accepted: 07/29/2015] [Indexed: 11/27/2022]
Abstract
Intralocus sexual conflict arises when selection favours alternative fitness optima in males and females. Unresolved conflict can create negative between-sex genetic correlations for fitness, such that high-fitness parents produce high-fitness progeny of their same sex, but low-fitness progeny of the opposite sex. This cost of sexual conflict could be mitigated if high-fitness parents bias sex allocation to produce more offspring of their same sex. Previous studies of the brown anole lizard (Anolis sagrei) show that viability selection on body size is sexually antagonistic, favouring large males and smaller females. However, sexual conflict over body size may be partially mitigated by adaptive sex allocation: large males sire more sons than daughters, whereas small males sire more daughters than sons. We explored the evolutionary implications of these phenomena by assessing the additive genetic (co)variance of fitness within and between sexes in a wild population. We measured two components of fitness: viability of adults over the breeding season, and the number of their progeny that survived to sexual maturity, which includes components of parental reproductive success and offspring viability (RS(V) ). Viability of parents was not correlated with adult viability of their sons or daughters. RS(V) was positively correlated between sires and their offspring, but not between dams and their offspring. Neither component of fitness was significantly heritable, and neither exhibited negative between-sex genetic correlations that would indicate unresolved sexual conflict. Rather, our results are more consistent with predictions regarding adaptive sex allocation in that, as the number of sons produced by a sire increased, the adult viability of his male progeny increased.
Collapse
Affiliation(s)
- R Calsbeek
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| | - M C Duryea
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| | - D Goedert
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA.,CAPES Foundation, Ministry of Education of Brazil, Brasília, DF, Brazil
| | - P Bergeron
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| | - R M Cox
- Department of Biological Sciences, Dartmouth College, Hanover, NH, USA
| |
Collapse
|
9
|
Romano A, Romano M, Caprioli M, Costanzo A, Parolini M, Rubolini D, Saino N. Sex allocation according to multiple sexually dimorphic traits of both parents in the barn swallow (Hirundo rustica). J Evol Biol 2015; 28:1234-47. [PMID: 25913917 DOI: 10.1111/jeb.12650] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2015] [Revised: 04/21/2015] [Accepted: 04/23/2015] [Indexed: 01/10/2023]
Abstract
Parents should differentially invest in sons or daughters depending on the sex-specific fitness returns from male and female offspring. In species with sexually selected heritable male characters, highly ornamented fathers should overproduce sons, which will be more sexually attractive than sons of less ornamented fathers. Because of genetic correlations between the sexes, females that express traits which are under selection in males should also overproduce sons. However, sex allocation strategies may consist in reaction norms leading to spatiotemporal variation in the association between offspring sex ratio (SR) and parental phenotype. We analysed offspring SR in barn swallows (Hirundo rustica) over 8 years in relation to two sexually dimorphic traits: tail length and melanin-based ventral plumage coloration. The proportion of sons increased with maternal plumage darkness and paternal tail length, consistently with sexual dimorphism in these traits. The size of the effect of these parental traits on SR was large compared to other studies of offspring SR in birds. Barn swallows thus manipulate offspring SR to overproduce 'sexy sons' and potentially to mitigate the costs of intralocus sexually antagonistic selection. Interannual variation in the relationships between offspring SR and parental traits was observed which may suggest phenotypic plasticity in sex allocation and provides a proximate explanation for inconsistent results of studies of sex allocation in relation to sexual ornamentation in birds.
Collapse
Affiliation(s)
- A Romano
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Romano
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Caprioli
- Department of Biosciences, University of Milan, Milan, Italy
| | - A Costanzo
- Department of Biosciences, University of Milan, Milan, Italy
| | - M Parolini
- Department of Biosciences, University of Milan, Milan, Italy
| | - D Rubolini
- Department of Biosciences, University of Milan, Milan, Italy
| | - N Saino
- Department of Biosciences, University of Milan, Milan, Italy
| |
Collapse
|
10
|
Patten MM. Meiotic drive influences the outcome of sexually antagonistic selection at a linked locus. J Evol Biol 2014; 27:2360-70. [DOI: 10.1111/jeb.12493] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 08/01/2014] [Accepted: 08/14/2014] [Indexed: 02/05/2023]
Affiliation(s)
- M. M. Patten
- Department of Biology; Georgetown University; Washington DC USA
| |
Collapse
|
11
|
Connallon T, Clark AG. Balancing selection in species with separate sexes: insights from Fisher's geometric model. Genetics 2014; 197:991-1006. [PMID: 24812306 PMCID: PMC4096376 DOI: 10.1534/genetics.114.165605] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 05/06/2014] [Indexed: 01/08/2023] Open
Abstract
How common is balancing selection, and what fraction of phenotypic variance is attributable to balanced polymorphisms? Despite decades of research, answers to these questions remain elusive. Moreover, there is no clear theoretical prediction about the frequency with which balancing selection is expected to arise within a population. Here, we use an extension of Fisher's geometric model of adaptation to predict the probability of balancing selection in a population with separate sexes, wherein polymorphism is potentially maintained by two forms of balancing selection: (1) heterozygote advantage, where heterozygous individuals at a locus have higher fitness than homozygous individuals, and (2) sexually antagonistic selection (a.k.a. intralocus sexual conflict), where the fitness of each sex is maximized by different genotypes at a locus. We show that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection. Although heterozygote advantage and sexual antagonism represent alternative mechanisms for maintaining polymorphism, they mutually exist along a balancing selection continuum that depends on population and sex-specific parameters of selection and mutation. Sexual antagonism is the dominant mode of balancing selection across most of this continuum.
Collapse
Affiliation(s)
- Tim Connallon
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853
| |
Collapse
|
12
|
Larsen CT, Holand AM, Jensen H, Steinsland I, Roulin A. On estimation and identifiability issues of sex-linked inheritance with a case study of pigmentation in Swiss barn owl (Tyto alba). Ecol Evol 2014; 4:1555-66. [PMID: 24967075 PMCID: PMC4063458 DOI: 10.1002/ece3.1032] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Revised: 01/30/2014] [Accepted: 01/31/2014] [Indexed: 11/25/2022] Open
Abstract
Genetic evaluation using animal models or pedigree-based models generally assume only autosomal inheritance. Bayesian animal models provide a flexible framework for genetic evaluation, and we show how the model readily can accommodate situations where the trait of interest is influenced by both autosomal and sex-linked inheritance. This allows for simultaneous calculation of autosomal and sex-chromosomal additive genetic effects. Inferences were performed using integrated nested Laplace approximations (INLA), a nonsampling-based Bayesian inference methodology. We provide a detailed description of how to calculate the inverse of the X- or Z-chromosomal additive genetic relationship matrix, needed for inference. The case study of eumelanic spot diameter in a Swiss barn owl (Tyto alba) population shows that this trait is substantially influenced by variation in genes on the Z-chromosome ( and ). Further, a simulation study for this study system shows that the animal model accounting for both autosomal and sex-chromosome-linked inheritance is identifiable, that is, the two effects can be distinguished, and provides accurate inference on the variance components.
Collapse
Affiliation(s)
- Camilla T Larsen
- Department of Mathematical Sciences, NTNU NO-7491, Trondheim, Norway
| | - Anna M Holand
- Department of Mathematical Sciences, Centre for Biodiversity Dynamics, NTNU NO-7491, Trondheim, Norway
| | - Henrik Jensen
- Department of Biology, Centre for Biodiversity Dynamics, NTNU NO-7491, Trondheim, Norway
| | - Ingelin Steinsland
- Department of Mathematical Sciences, Centre for Biodiversity Dynamics, NTNU NO-7491, Trondheim, Norway
| | - Alexandre Roulin
- Department of Ecology and Evolution, University of Lausanne 1015, Lausanne, Switzerland
| |
Collapse
|
13
|
Pennell TM, Morrow EH. Two sexes, one genome: the evolutionary dynamics of intralocus sexual conflict. Ecol Evol 2013; 3:1819-34. [PMID: 23789088 PMCID: PMC3686212 DOI: 10.1002/ece3.540] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Revised: 03/01/2013] [Accepted: 03/09/2013] [Indexed: 11/10/2022] Open
Abstract
As the evolutionary interests of males and females are frequently divergent, a trait value that is optimal for the fitness of one sex is often not optimal for the other. A shared genome also means that the same genes may underlie the same trait in both sexes. This can give rise to a form of sexual antagonism, known as intralocus sexual conflict (IASC). Here, a tug-of-war over allelic expression can occur, preventing the sexes from reaching optimal trait values, thereby causing sex-specific reductions in fitness. For some traits, it appears that IASC can be resolved via sex-specific regulation of genes that subsequently permits sexual dimorphism; however, it seems that whole-genome resolution may be impossible, due to the genetic architecture of certain traits, and possibly due to the changing dynamics of selection. In this review, we explore the evolutionary mechanisms of, and barriers to, IASC resolution. We also address the broader consequences of this evolutionary feud, the possible interactions between intra- and interlocus sexual conflict (IRSC: a form of sexual antagonism involving different loci in each sex), and draw attention to issues that arise from using proxies as measurements of conflict. In particular, it is clear that the sex-specific fitness consequences of sexual dimorphism require characterization before making assumptions concerning how this relates to IASC. Although empirical data have shown consistent evidence of the fitness effects of IASC, it is essential that we identify the alleles mediating these effects in order to show IASC in its true sense, which is a “conflict over shared genes.”
Collapse
Affiliation(s)
- Tanya M Pennell
- Evolution, Behaviour and Environment Group, School of Life Sciences, University of Sussex Falmer, East Sussex, BN1 9QG, UK
| | | |
Collapse
|
14
|
Kuijper B, Pen I, Weissing FJ. A Guide to Sexual Selection Theory. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2012. [DOI: 10.1146/annurev-ecolsys-110411-160245] [Citation(s) in RCA: 151] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mathematical models have played an important role in the development of sexual selection theory. These models come in different flavors and they differ in their assumptions, often in a subtle way. Similar questions can be addressed by modeling frameworks from population genetics, quantitative genetics, evolutionary game theory, or adaptive dynamics, or by individual-based simulations. Confronted with such diversity, nonspecialists may have difficulties judging the scope and limitations of the various approaches. Here we review the major modeling frameworks, highlighting their pros and cons when applied to different research questions. We also discuss recent developments, where classical models are enriched by including more detail regarding genetics, behavior, demography, and population dynamics. It turns out that some seemingly well-established conclusions of sexual selection theory are less general than previously thought. Linking sexual selection to other processes such as sex-ratio evolution or speciation also reveals that enriching the theory can lead to surprising new insights.
Collapse
Affiliation(s)
- Bram Kuijper
- Theoretical Biology Group, Center for Ecological and Evolutionary Studies, University of Groningen, 9747 AG Groningen, The Netherlands;, ,
- Behavior and Evolution Group, Department of Zoology, University of Cambridge, CB2 3EJ Cambridge, United Kingdom
| | - Ido Pen
- Theoretical Biology Group, Center for Ecological and Evolutionary Studies, University of Groningen, 9747 AG Groningen, The Netherlands;, ,
| | - Franz J. Weissing
- Theoretical Biology Group, Center for Ecological and Evolutionary Studies, University of Groningen, 9747 AG Groningen, The Netherlands;, ,
| |
Collapse
|
15
|
Katsuki M, Harano T, Miyatake T, Okada K, Hosken DJ. Intralocus sexual conflict and offspring sex ratio. Ecol Lett 2012; 15:193-7. [PMID: 22225600 DOI: 10.1111/j.1461-0248.2011.01725.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Males and females frequently have different fitness optima for shared traits, and as a result, genotypes that are high fitness as males are low fitness as females, and vice versa. When this occurs, biasing of offspring sex-ratio to reduce the production of the lower-fitness sex would be advantageous, so that for example, broods produced by high-fitness females should contain fewer sons. We tested for offspring sex-ratio biasing consistent with these predictions in broad-horned flour beetles. We found that in both wild-type beetles and populations subject to artificial selection for high- and low-fitness males, offspring sex ratios were biased in the predicted direction: low-fitness females produced an excess of sons, whereas high-fitness females produced an excess of daughters. Thus, these beetles are able to adaptively bias sex ratio and recoup indirect fitness benefits of mate choice.
Collapse
Affiliation(s)
- Masako Katsuki
- Graduate School of Environmental Science, Okayama University, Tsushima-naka 1-1-1, Okayama, Japan
| | | | | | | | | |
Collapse
|
16
|
Sex-ratio control erodes sexual selection, revealing evolutionary feedback from adaptive plasticity. Proc Natl Acad Sci U S A 2011; 108:15925-30. [PMID: 21911375 DOI: 10.1073/pnas.1105721108] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Female choice is a powerful selective force, driving the elaboration of conspicuous male ornaments. This process of sexual selection has profound implications for many life-history decisions, including sex allocation. For example, females with attractive partners should produce more sons, because these sons will inherit their father's attractiveness and enjoy high mating success, thereby yielding greater fitness returns than daughters. However, previous research has overlooked the fact that there is a reciprocal feedback from life-history strategies to sexual selection. Here, using a simple mathematical model, we show that if mothers adaptively control offspring sex in relation to their partner's attractiveness, sexual selection is weakened and male ornamentation declines. This weakening occurs because the ability to determine offspring sex reduces the fitness difference between females with attractive and unattractive partners. We use individual-based, evolutionary simulations to show that this result holds under more biologically realistic conditions. Sexual selection and sex allocation thus interact in a dynamic fashion: The evolution of conspicuous male ornaments favors sex-ratio adjustment, but this conditional strategy then undermines the very same process that generated it, eroding sexual selection. We predict that, all else being equal, the most elaborate sexual displays should be seen in species with little or no control over offspring sex. The feedback process we have described points to a more general evolutionary principle, in which a conditional strategy weakens directional selection on another trait by reducing fitness differences.
Collapse
|
17
|
Abstract
Disruptive selection between males and females can generate sexual antagonism, where alleles improving fitness in one sex reduce fitness in the other. This type of genetic conflict arises because males and females carry nearly identical sets of genes: opposing selection, followed by genetic mixing during reproduction, generates a population genetic "tug-of-war" that constrains adaptation in either sex. Recent verbal models suggest that gene duplication and sex-specific cooption of paralogs might resolve sexual antagonism and facilitate evolutionary divergence between the sexes. However, this intuitive proximal solution for sexual dimorphism potentially belies a complex interaction between mutation, genetic drift, and positive selection during duplicate fixation and sex-specific paralog differentiation. The interaction of these processes--within the explicit context of duplication and sexual antagonism--has yet to be formally described by population genetics theory. Here, we develop and analyze models of gene duplication and sex-specific differentiation between paralogs. We show that sexual antagonism can favor the fixation and maintenance of gene duplicates, eventually leading to the evolution of sexually dimorphic genetic architectures for male and female traits. The timescale for these evolutionary transitions is sensitive to a suite of genetic and demographic variables, including allelic dominance, recombination, sex linkage, and population size. Interestingly, we find that female-beneficial duplicates preferentially accumulate on the X chromosome, whereas male-beneficial duplicates are biased toward autosomes, independent of the dominance parameters of sexually antagonistic alleles. Although this result differs from previous models of sexual antagonism, it is consistent with several findings from the empirical genomics literature.
Collapse
|
18
|
Connallon T, Clark AG. Sex linkage, sex-specific selection, and the role of recombination in the evolution of sexually dimorphic gene expression. Evolution 2010; 64:3417-42. [PMID: 20874735 PMCID: PMC2998557 DOI: 10.1111/j.1558-5646.2010.01136.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sex-biased genes--genes that are differentially expressed within males and females--are nonrandomly distributed across animal genomes, with sex chromosomes and autosomes often carrying markedly different concentrations of male- and female-biased genes. These linkage patterns are often gene- and lineage-dependent, differing between functional genetic categories and between species. Although sex-specific selection is often hypothesized to shape the evolution of sex-linked and autosomal gene content, population genetics theory has yet to account for many of the gene- and lineage-specific idiosyncrasies emerging from the empirical literature. With the goal of improving the connection between evolutionary theory and a rapidly growing body of genome-wide empirical studies, we extend previous population genetics theory of sex-specific selection by developing and analyzing a biologically informed model that incorporates sex linkage, pleiotropy, recombination, and epistasis, factors that are likely to vary between genes and between species. Our results demonstrate that sex-specific selection and sex-specific recombination rates can generate, and are compatible with, the gene- and species-specific linkage patterns reported in the genomics literature. The theory suggests that sexual selection may strongly influence the architectures of animal genomes, as well as the chromosomal distribution of fixed substitutions underlying sexually dimorphic traits.
Collapse
Affiliation(s)
- Tim Connallon
- Department of Molecular Biology & Genetics, Cornell University, Ithaca, New York 14853-2703, USA.
| | | |
Collapse
|