Female-limited X-chromosome evolution in Drosophila
This project is a follow-up to a previous investigation of male-limited X-chromosome (MLX) evolution in Drosophila melanogaster. By using an FM balancer chromosome, I can force the X to only be expressed in females for many generations. This will result in a relaxation of counter-selection in males, and cause the X to evolve to maximize female fitness. The female-limited X-chromosome evolution (FLX) experiment will therefore help to resolve a number of outstanding questions, for example whether the magnitude of the response is the same in FLX evolution as in MLX evolution, and whether it is the same traits which respond. Males are generally expected to be subject to stronger sexual selection than females, so it is possible that both sexes are displaced towards the male optimum for such traits. In that case I would expect to see a larger change as result of FLX evolution in traits that are sexually selected in males (but not male-limited in expression) relative to traits that are subject to natural selection in either sex.
A final exciting question which the FLX experiment may be able to shed some light on is the importance and nature of dominance and epistasis in Drosophila. By expressing evolved X-chromosomes in females in a heterozygous (i.e. one FLX-evolved X-chromosome and one Control X-chromosome) or homozygous (i.e. two FLX-evolved X-chromosomes) state, I will be able to test for fitness-related dominance and epistatic variance on the X-chromosome in Drosophila. Theory suggests that dominance should be important for X-linked sexually antagonistic genetic variation, and result from the MLX experiment suggest that epistatic interactions between the X-chromosome and the autosomes are common for sexually antagonistic loci.