Males evolved extravagant plumage, towering antlers, and frenetic mating displays, Darwin proposed, because that's what females like. Selection on secondary sexual characteristics often results in sexually dimorphic traits being tailored toward the specific reproductive needs of each sex, and sexual dimorphism typically arises because selection operates in different directions on each gender--selecting for large males and compact females, for example--promoting sex-specific gene expression. But when selection acts on a shared trait and the sexes are genetically constrained from becoming dimorphic, "intralocus" sexual conflict can occur. In a new study, Alison Pischedda and Adam Chippindale explore the potential costs of intralocus sexual conflict in the genetically tractable fruit fly, Drosophila melanogaster. By measuring the inheritance of fitness across generations, and across the genome, they show that sexual selection provides no advantage to the next generation. To the contrary, having a fit parent of the opposite sex leads to dramatically lower rates of reproductive success. Sexually antagonistic genes, it appears, may have far-reaching effects on patterns of fitness inheritance.
Using a recently developed genetic tool called hemiclonal analysis, researchers can screen the (nearly) entire genome for genetic variation within a population and for evidence of selection acting on that variation. Pischedda and Chippindale used hemiclonal analysis to generate high- and low-fitness parents, and selected three lines of the most and least fit mothers and fathers, based on egg production and number of offspring sired. High-fitness females laid 35% more eggs than low-fitness females; high-fitness males fathered 44% more offspring than their less-fit counterparts. After crossing every possible combination of high- and low-fitness parental lines (yielding 36 crosses), the authors evaluated fitness effects on offspring to determine patterns of fitness inherit
Contact: Natalie Bouaravong
Public Library of Science