Is sex chromosome evolution driven by sexual antagonism? A test with houseflies

Sexual antagonism or sexual conflict occurs when the two sexes have divergent optimal fitness strategies concerning reproduction. The importance of this phenomenon in driving evolutionary changes in development and behaviour is still debated. In this proposal we investigate the role of sexual antagonism in the evolution of sex chromosomes, by combining theoretical and experimental approaches to the polymorphic sex determination system of the housefly. Housefly populations carry male-determining factors on different chromosomes and possess two different female determiners. Our objectives are to determine 1) the coevolutionary dynamics of sex determination (SD) and sexually anatagonistic (SA) genes; 2) how SA and SD genes are distributed in the housefly genome, and how this is affected by recombination on standard and neo-sex chromosomes in males and females; and 3) whether neo-sex chromosomes undergo accumulation of genes with sex-limited expression (sexualisation of gene content).
We will use evolutionary models to study the coevolutionary dynamics of sexual antagonism and sex determination caused by interactions between male courtship behaviour and sex peptides, body size of both sexes, and female sex peptide receptors and mating preferences. We will measure recombination rates of autosomes and (neo-) chromosomes with molecular markers. The degree and genetic basis of sexually antagonistic selection in houseflies will be measured with interpopulation crosses and genomic screens for candidate loci. We will apply artificial selection and transmission of neo-sex chromosomes through one sex by experimental evolution, combined with transcriptomic analyses, in order to investigate sexualisation of sex chromosome gene content. The results will shed light on how sexual antagonism can drive evolutionary processes at the genomic level.