Sexual conflict · Genetic architecture of intralocus sexual conflict in a wild bird population

Genetic architecture of intralocus sexual conflict in a wild bird population

Males and females are typically dimorphic for a large number of phenotypic traits. Such sexual dimorphism (SD) is generally believed to be adaptive, reflecting difference in sex-specific phenotypic optima. While the widespread occurrence of SD indicates that its evolution is possible, large genetic correlations between most homologous male and female traits suggest that the short-term evolution of SD may generally be constrained. Indeed, whenever selection differs between the sexes for a trait or set of traits that is genetically correlated between the sexes, there is potential for the effect of selection in one sex to be altered by indirect selection in the other sex, a situation generally referred to as intralocus sexual conflict (ISC). While potentially common and important, such conflicts remain little studied in natural populations. In this project the genetic architecture and fitness consequences of ISC was studied in a wild population of great tits from Wytham Woods, Oxford. Sex-specific quantitative genetic parameters (additive genetic (co)variances) and selection coefficients were estimated for a set of sexually dimorphic morphological traits (bill width, bill length, wing length, tarsus length) using pedigree and lifetime reproductive success (LRS) data collected over multiple decades. A multivariate statistical framework was then used to predict micro-evolutionary responses and estimate the fitness consequences of sex-specific effects. Results indicated that studied morphological traits were highly heritable and generally influenced by the same genes in both sexes. Selection analyses indicated the presence of significant multivariate selection, without any evidence for a sex by selection interaction. Together, sex-specific additive genetic effects and multivariate selection generated predicted genetic variance in relative fitness explaining less than 1% of the phenotypic variation in relative fitness. Cross-sex genetic covariances were found to (non-significantly) increase the predicted rate of adaptation relative to a situation where traits were not genetically correlated between the sexes. Finally, the presence of separate genders, relative to a situation where there would be no sex-specific selection and genetic variance, was found to result in a decrease in the predicted rate of adaptation. Overall, this research project made significant contributions to our understanding of the evolutionary dynamic of sexual dimorphism in an important ecological model organism. It also contributed to the development of a multivariate framework to quantify the fitness consequences of sex-specific selection in wild populations. Increased knowledge about the genetic basis of sex-specific fitness will allow for a better understanding of the role of sexually antagonistic selection in maintaining genetic variation, developing more realistic sexual selection models, better understanding population dynamics and assessing the importance of sexual dimorphism in the speciation process. General knowledge about the genetic basis and evolutionary dynamic of sexual dimorphism is also highly pertinent to plant and animal breeding as well as human medical genetics.

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