Evolutionary Consequences of Sex Linkage and Sex-Specific Selection.

Abstract

Males and females make equal genetic contributions to each generation, yet each sex is exposed to different, sometimes opposing forces of natural and sexual selection. Because males and females are part of a common gene pool, “sex-specific selection” – selection differing between males and females in strength and/or direction – can potentially have major population genetic and adaptive consequences for sexually reproducing species. When selection follows the same trajectory in both sexes and acts more strongly in males, sex-specific selection facilitates adaptation. However, opposing selection between the sexes can also generate genomic conflict over the outcome of evolution. Such “sexually antagonistic selection” represents an adaptive constraint for sexually reproducing species.

Despite its potential importance, theoretical and empirical studies in evolutionary genetics often overlook sex-specific selection. Though this neglect is beginning to be remedied, a thorough understanding of the adaptive consequences of sex-specific selection is currently lacking. This dissertation represents an attempt to better understand the evolutionary genetic consequences of sex-specific selection, and specifically focuses on three related questions: (A) Is adaptation enhanced or constrained by sex-linked inheritance, which theory predicts should enhance opportunities for sex-specific selection? (B) How do sex linkage and processes of sex-specific selection interact to influence patterns of fitness heritability between parents and offspring? (C) What are the long-term adaptive consequences of sexual reproduction on population fitness and the genetic load of deleterious mutations?

These questions are addressed using a combination of mathematical theory, bioinformatics and comparative genomics techniques, and quantitative genetic experiments using the fruit fly Drosophila melanogaster. The theoretical and empirical aspects of the dissertation confirm that sex-specific selection is an important evolutionary consideration and that it generates both adaptive benefits and adaptive costs for sexually reproducing species.