Sexually antagonistic selection during parental care is not generated by a testosterone-related intralocus sexual conflict–insights from full-sib comparisons

The reproductive interests of males and females will almost always differ, for example over whether to mate and how often, when to produce offspring and how many, or how much to invest in each offspring. Whenever the reproductive interests of males and females differ, opposing selection on males and females to achieve their preferred outcome will generate sexually antagonistic selection. Such sexual conflict is reflected in differences in the appearance and behaviour of the sexes as each evolves to gain the advantage in a fitness ‘arms race’. ‘Sexual conflict’ explores the evolutionary consequences of these arms races in the context of sexual selection as it occurs both before and after mating.

Download Full-text

Sex-Specific Selection and the Evolution of Between-Sex Genetic Covariance

Journal of Heredity ◽

10.1093/jhered/esz031 ◽

2019 ◽

Vol 110 (4) ◽

pp. 422-432 ◽

Cited By ~ 8

Author(s):

Joel W McGlothlin ◽

Robert M Cox ◽

Edmund D Brodie

Keyword(s):

Genetic Correlations ◽

Relative Strength ◽

Directional Selection ◽

Genetic Covariance ◽

Empirical Measures ◽

Antagonistic Selection ◽

Intralocus Sexual Conflict ◽

A Genome ◽

Brown Anole ◽

Sexually Antagonistic Selection

Abstract Because the sexes share a genome, traits expressed in males are usually genetically correlated with the same traits expressed in females. On short timescales, between-sex genetic correlations (rmf) for shared traits may constrain the evolution of sexual dimorphism by preventing males and females from responding independently to sex-specific selection. However, over longer timescales, rmf may evolve, thereby facilitating the evolution of dimorphism. Although it has been suggested that sexually antagonistic selection may reduce rmf, we lack a general theory for the evolution of rmf and its multivariate analog, the between-sex genetic covariance matrix (B). Here, we derive a simple analytical model for the within-generation change in B due to sex-specific directional selection. We present a single-trait example demonstrating that sex-specific directional selection may either increase or decrease between-sex genetic covariance, depending on the relative strength of selection in each sex and on the current value of rmf. Although sexually antagonistic selection can reduce between-sex covariance, it will only do so when selection is much stronger in one sex than in the other. Counterintuitively, sexually antagonistic selection that is equal in strength in the 2 sexes will maintain positive between-sex covariance. Selection acting in the same direction on both sexes is predicted to reduce between-sex covariance in many cases. We illustrate our model numerically using empirical measures of sex-specific selection and between-sex genetic covariance from 2 populations of sexually dimorphic brown anole lizards (Anolis sagrei) and discuss its importance for understanding the resolution of intralocus sexual conflict.

Download Full-text

Constraints on the coevolution of contemporary human males and females

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2012.2024 ◽

2012 ◽

Vol 279 (1748) ◽

pp. 4836-4844 ◽

Cited By ~ 50

Author(s):

Stephen C. Stearns ◽

Diddahally R. Govindaraju ◽

Douglas Ewbank ◽

Sean G. Byars

Keyword(s):

Sexual Conflict ◽

Age At First Birth ◽

Male And Female ◽

Selection Gradients ◽

Intralocus Sexual Conflict ◽

Individual Traits ◽

Sexually Antagonistic Selection ◽

Males And Females ◽

Female Responses ◽

Genetic Covariances

Because autosomal genes in sexually reproducing organisms spend on average half their time in each sex, and because the traits that they influence encounter different selection pressures in males and females, the evolutionary responses of one sex are constrained by processes occurring in the other sex. Although intralocus sexual conflict can restrict sexes from reaching their phenotypic optima, no direct evidence currently supports its operation in humans. Here, we show that the pattern of multivariate selection acting on human height, weight, blood pressure and glucose, total cholesterol, and age at first birth differs significantly between males and females, and that the angles between male and female linear (77.8 ± 20.5°) and nonlinear (99.1 ± 25.9°) selection gradients were closer to orthogonal than zero, confirming the presence of sexually antagonistic selection. We also found evidence for intralocus sexual conflict demonstrated by significant changes in the predicted male and female responses to selection of individual traits when cross-sex genetic covariances were included and a significant reduction in the angle between male- and female-predicted responses when cross-sex covariances were included (16.9 ± 15.7°), compared with when they were excluded (87.9 ± 31.6°). We conclude that intralocus sexual conflict constrains the joint evolutionary responses of the two sexes in a contemporary human population.

Download Full-text

Intralocus sexual conflict for fitness: sexually antagonistic alleles for testosterone

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2011.2340 ◽

2011 ◽

Vol 279 (1735) ◽

pp. 1889-1895 ◽

Cited By ~ 39

Author(s):

Suzanne C. Mills ◽

Esa Koskela ◽

Tapio Mappes

Keyword(s):

Negative Correlation ◽

Sexual Conflict ◽

Bank Vole ◽

Genetic Locus ◽

Myodes Glareolus ◽

Phenotypic Traits ◽

Intralocus Sexual Conflict ◽

Opposite Sex ◽

Sexually Antagonistic Selection ◽

Males And Females

Intralocus sexual conflict occurs when a trait encoded by the same genetic locus in the two sexes has different optima in males and females. Such conflict is widespread across taxa, however, the shared phenotypic traits that mediate the conflict are largely unknown. We examined whether the sex hormone, testosterone (T), that controls sexual differentiation, contributes to sexually antagonistic fitness variation in the bank vole, Myodes glareolus . We compared (opposite-sex) sibling reproductive fitness in the bank vole after creating divergent selection lines for T. This study shows that selection for T was differentially associated with son versus daughter reproductive success, causing a negative correlation in fitness between full siblings. Our results demonstrate the presence of intralocus sexual conflict for fitness in this small mammal and that sexually antagonistic selection is acting on T. We also found a negative correlation in fitness between parents and their opposite-sex progeny (e.g. father–daughter), highlighting a dilemma for females, as the indirect genetic benefits of selecting reproductively successful males (high T) are lost with daughters. We discuss mechanisms that may mitigate this disparity between progeny quality.

Download Full-text