RUNAWAY SEXUAL SELECTION WITHOUT GENETIC CORRELATIONS: SOCIAL ENVIRONMENTS AND FLEXIBLE MATE CHOICE INITIATE AND ENHANCE THE FISHER PROCESS

Abstract A key element at the heart of the Fisher–Lande–Kirkpatrick model of the sexual selection process is the genetic correlation between (male) trait and (female) preference. The strength of this association is critical in determining a population’s evolutionary trajectory, which is why estimating its magnitude is so important. In the Lande model, the trait-preference correlation is solely established and maintained by mate choice, and although it is unclear how exclusively mate choice does this in nature, the experimental designs typically employed to measure trait-preference genetic correlations could be systematically weakening estimates by not allowing free mate choice (similarly with husbandry practices). The precise impact of the problem is unknown, and possibly unknowable, but simple solutions can be applied to ensure the accuracy of trait-preference correlation estimates is maximized.

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Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait

Nature Communications ◽

10.1038/s41467-021-23804-7 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Kensuke Okada ◽

Masako Katsuki ◽

Manmohan D. Sharma ◽

Katsuya Kiyose ◽

Tomokazu Seko ◽

...

Keyword(s):

Sexual Selection ◽

Natural Selection ◽

Experimental Evolution ◽

Genetic Correlations ◽

Lifetime Reproductive Success ◽

Fundamental Theory ◽

Female Fitness ◽

Male Trait ◽

Flour Beetles ◽

Male Specific

AbstractTheory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters.

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Gamete-mediated mate choice: towards a more inclusive view of sexual selection

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2018.0836 ◽

2018 ◽

Vol 285 (1883) ◽

pp. 20180836 ◽

Cited By ~ 21

Author(s):

Jukka Kekäläinen ◽

Jonathan P. Evans

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Sperm Competition ◽

Female Choice ◽

Mating Systems ◽

Molecular Level ◽

Evolutionary Significance ◽

Random Interactions ◽

Physiological Processes ◽

The Everyday

‘Sperm competition’—where ejaculates from two or more males compete for fertilization—and ‘cryptic female choice’—where females bias this contest to suit their reproductive interests—are now part of the everyday lexicon of sexual selection. Yet the physiological processes that underlie these post-ejaculatory episodes of sexual selection remain largely enigmatic. In this review, we focus on a range of post-ejaculatory cellular- and molecular-level processes, known to be fundamental for fertilization across most (if not all) sexually reproducing species, and point to their putative role in facilitating sexual selection at the level of the cells and gametes, called ‘gamete-mediated mate choice’ (GMMC). In this way, we collate accumulated evidence for GMMC across different mating systems, and emphasize the evolutionary significance of such non-random interactions among gametes. Our overall aim in this review is to build a more inclusive view of sexual selection by showing that mate choice often acts in more nuanced ways than has traditionally been assumed. We also aim to bridge the conceptual divide between proximal mechanisms of reproduction, and adaptive explanations for patterns of non-random sperm–egg interactions that are emerging across an increasingly diverse array of taxa.

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Mate Choice, Sex Roles and Sexual Cognition in Vertebrates: Mate Choice Turns Cognition or Cognition Turns Mate Choice?

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.749495 ◽

2021 ◽

Vol 9 ◽

Author(s):

Theodora Fuss

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Mating System ◽

Cognitive Abilities ◽

Cognitive Skills ◽

Sex Roles ◽

Environmental Changes ◽

Antipredator Behavior ◽

Energy Levels ◽

Problem Solver

The idea of “smart is sexy,” meaning superior cognition provides competitive benefits in mate choice and, therefore, evolutionary advantages in terms of reproductive fitness, is both exciting and captivating. Cognitively flexible individuals perceive and adapt more dynamically to (unpredictable) environmental changes. The sex roles that females and males adopt within their populations can vary greatly in response to the prevalent mating system. Based on how cognition determines these grossly divergent sex roles, different selection pressures could possibly shape the (progressive) evolution of cognitive abilities, suggesting the potential to induce sexual dimorphisms in superior cognitive abilities. Associations between an individual’s mating success, sexual traits and its cognitive abilities have been found consistently across vertebrate species and taxa, providing evidence that sexual selection may well shape the supporting cognitive prerequisites. Yet, while superior cognitive abilities provide benefits such as higher feeding success, improved antipredator behavior, or more favorable mate choice, they also claim costs such as higher energy levels and metabolic rates, which in turn may reduce fecundity, growth, or immune response. There is compelling evidence in a variety of vertebrate taxa that females appear to prefer skilled problem-solver males, i.e., they prefer those that appear to have better cognitive abilities. Consequently, cognition is also likely to have substantial effects on sexual selection processes. How the choosing sex assesses the cognitive abilities of potential mates has not been explored conclusively yet. Do cognitive skills guide an individual’s mate choice and does learning change an individual’s mate choice decisions? How and to which extent do individuals use their own cognitive skills to assess those of their conspecifics when choosing a mate? How does an individual’s role within a mating system influence the choice of the choosing sex in this context? Drawing on several examples from the vertebrate world, this review aims to elucidate various aspects associated with cognitive sex differences, the different roles of males and females in social and sexual interactions, and the potential influence of cognition on mate choice decisions. Finally, future perspectives aim to identify ways to answer the central question of how the triad of sex, cognition, and mate choice interacts.

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Sexual Selection and Mate Choice: Insights from Neutralist Perspectives

Evolutionary Biology ◽

10.1007/s11692-015-9315-x ◽

2015 ◽

Vol 42 (3) ◽

pp. 366-378 ◽

Cited By ~ 6

Author(s):

Austin L. Hughes

Keyword(s):

Sexual Selection ◽

Mate Choice

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4. Sex roles and stereotypes

Sexual Selection: A Very Short Introduction ◽

10.1093/actrade/9780198778752.003.0004 ◽

2018 ◽

pp. 52-68

Author(s):

Leigh W. Simmons

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Sexual Behaviour ◽

Sex Roles ◽

Animal Species ◽

Male And Female ◽

Mating Competition ◽

Characteristic Behaviour ◽

Males And Females ◽

Female Roles

‘Sex roles and stereotypes’ examines the notion, implicit in many of the original ideas about sexual selection, that males and females have natural ‘roles’ with characteristic behaviour associated with each sex. It also explores further the reasons behind deviations from the ‘typical’ sex roles in mate choice and in mating competition. Are there ‘standard’ male and female roles in both humans and other animal species? One version of sex roles holds that males are generally dominant and females submissive, stemming from the way that sexual selection favours different behaviours in each sex. This could mean that sexual selection dictates particular behaviours in males and females. But in fact, sexual behaviour is extraordinarily varied in nature.

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Synthesis and Outlook

Male Choice, Female Competition, and Female Ornaments in Sexual Selection ◽

10.1093/oso/9780198818946.003.0009 ◽

2021 ◽

pp. 153-161

Author(s):

Ingo Schlupp

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Sex Ratios ◽

Empirical Work ◽

Male Mate Choice ◽

Female Ornamentation ◽

Female Quality ◽

Investment In Reproduction ◽

Selection Research ◽

Male Mate

In this final chapter I want to briefly recap what I presented in the previous chapters and provide a few ideas on what might be done in the future to move the field forward. All three factors I discussed as relevant in male mate choice—male investment in reproduction, sex ratios, and variability in partner quality—are still emerging fields in sexual selection research and need more theoretical and empirical work. I suggest that variability in female quality is more important and more complex than currently known. The same is true for sex ratios. On the other hand, I suggest that sheer investment in gametes may be a little less important than currently assumed. Most importantly we need to explore the interactions of these three pathways to male mate choice. Female competition and also female ornamentation are still somewhat enigmatic and both topics are likely to grow in importance for our understanding of sexual selection. I think considering male and female choice together, as well as female and male competition will ultimately provide a more complete picture of Darwinian sexual selection.

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Sexual selection after gamete release in broadcast spawning invertebrates

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0069 ◽

2020 ◽

Vol 375 (1813) ◽

pp. 20200069 ◽

Cited By ~ 2

Author(s):

Jonathan P. Evans ◽

Rowan A. Lymbery

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Sperm Competition ◽

Sexual Conflict ◽

Gamete Release ◽

Theme Issue ◽

Animal Kingdom ◽

External Fertilization ◽

Broadcast Spawning ◽

Males And Females

Broadcast spawning invertebrates offer highly tractable models for evaluating sperm competition, gamete-level mate choice and sexual conflict. By displaying the ancestral mating strategy of external fertilization, where sexual selection is constrained to act after gamete release, broadcast spawners also offer potential evolutionary insights into the cascade of events that led to sexual reproduction in more ‘derived’ groups (including humans). Moreover, the dynamic reproductive conditions faced by these animals mean that the strength and direction of sexual selection on both males and females can vary considerably. These attributes make broadcast spawning invertebrate systems uniquely suited to testing, extending, and sometimes challenging classic and contemporary ideas in sperm competition, many of which were first captured in Parker's seminal papers on the topic. Here, we provide a synthesis outlining progress in these fields, and highlight the burgeoning potential for broadcast spawners to provide both evolutionary and mechanistic understanding into gamete-level sexual selection more broadly across the animal kingdom. This article is part of the theme issue ‘Fifty years of sperm competition’.

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Mate Choice Contributes to the Maintenance of Shell Color Polymorphism in a Marine Snail via Frequency-Dependent Sexual Selection

Frontiers in Marine Science ◽

10.3389/fmars.2020.614237 ◽

2020 ◽

Vol 7 ◽

Author(s):

Daniel Estévez ◽

Eugene Kozminsky ◽

Antonio Carvajal-Rodríguez ◽

Armando Caballero ◽

Rui Faria ◽

...

Keyword(s):

Sexual Selection ◽

Mate Choice ◽

Color Polymorphism ◽

Snail Species ◽

Effective Population ◽

Evolutionary Mechanisms ◽

Shell Color ◽

Frequency Dependent ◽

Ideal System ◽

Frequency Changes

Natural color polymorphisms are widespread across animal species and usually have a simple genetic basis. This makes them an ideal system to study the evolutionary mechanisms responsible for maintaining biodiversity. In some populations of the intertidal snail Littorina fabalis, variation in shell color has remained stable for years, but the mechanisms responsible are unknown. Previous studies suggest that this stability could be caused by frequency-dependent sexual selection, but this hypothesis has not been tested. We analyzed shell color polymorphism in mating pairs and surrounding unmated individuals in two different populations of L. fabalis to estimate sexual fitness for color, as well as assortative mating. The estimated effective population size from neutral markers allowed us to disregard genetic drift as the main source of color frequency changes across generations. Shell color frequency was significantly correlated with sexual fitness showing a pattern of negative frequency dependent selection with high disassortative mating for color. The results suggested a contribution of male mate choice to maintain the polymorphism. Finally, the implementation of a multi-model inference approach based on information theory allowed us to test for the relative contribution of mate choice and mate competition to explain the maintenance of color polymorphism in this snail species.

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