The genomic and transcriptomic locus of sex-specific selection in birds

Final Report Summary - AVIAN DIMORPHISM (The genomic and transcriptomic locus of sex-specific selection in birds)

In this project, I used population and molecular genetic tools to ask fundamental questions in evolution and behavioral ecology related to how sexual selection affects the genome, and how the genome responds to contradictory selection in males and females to encode sexually dimorphic phenotypes. Work from this project has shown that sexual selection is a major force, and is as important as natural selection, in genome evolution. More specifically, my lab recently provided the first direct empirical evidence that sexual selection, in addition to shaping gene expression and sequence evolution on existing sex chromosomes, is the primary force precipitating sex chromosome formation.
How does transcriptional dimorphism encode phenotypic dimorphism?
By capitalizing on various forms of intra-sexual variation, my lab tested the predictions linking sex-biased gene expression and sexual dimorphism across multiple levels of biological diversity, including through development, within populations, across populations, and among species. Our results draw a clear relationship between a large proportion of sex-biased genes and phenotypic dimorphism, and are fundamental for my work identifying the force and loci of sexual selection within the genome, described below. More broadly, my results identified a large number of loci involved in sexual dimorphism, implying an extraordinary complexity to dimorphic phenotypes and suggesting an architecture of many loci of small effect.
How does is the genomes shaped by different sexual ecologies?
The genome is subject to different sexual selection pressures depending on mating system, and although we have a clear phenotypic understanding of sexual selection, it was unclear how sexual selection acts on the genome. In order to critically test long-standing theory regarding the nature and locus of sexual selection within the genome, I developed methods to study the footprint of sexual selection on gene sequence and expression. Our results are the first to show that sexual selection is as important a force as natural selection in shaping broad patterns of gene sequence, expression and genome evolution.
How does sexual selection influence sex chromosome evolution?
There is a complex relationship intertwining sexual selection, sexual conflict and sex chromosome evolution. Once formed, sex chromosomes are the only regions of the genome that differ in presence or dose between females and males, and are therefore predicted to become genomic hotspots for sexual conflict. However, sexual conflict is also thought to precipitate the formation of the sex chromosomes. I have used genomic and transcriptomic comparisons between the sex chromosomes and autosomes to differentiate cause from effect in the relationship between sexual conflict and sex chromosomes, to critically test the long-hypothesized role of sex chromosomes in encoding sexually dimorphic traits, and most recently to provide the first direct empirical evidence that sexual selection catalyzes sex chromosome formation. Our work has been key in disentangling the cause and effect of sexual selection on sex chromosome evolution, and more broadly for testing theory and revealing the potential of the sex chromosomes in the origin of sexual dimorphism.

Final Report Summary - AVIAN DIMORPHISM (The genomic and transcriptomic locus of sex-specific selection in birds)

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