March 30 2010

12:00 BSRB 154

Ecolunch: Malin Ah-King
UCLA Ecology & Evolutionary Biology

Why evolve sex chromosomes? Testing a hypothesis of parental conflict over offspring sex ratio


The diversity in sex determination mechanisms in animals is enormous, shifting frequently between genetic and environmental sex determination and female and male heterogametic systems. Several explanations have been proposed to account for the evolution of sex determining mechanisms, however, most of these explanations are proximate. Here we suggest a novel ultimate hypothesis, that parental conflict over sex ratio is an important selective force favouring the evolution of heterogamety. The heterogametic sex can be seen as a momentary winner of the conflict. Once heterogamety has evolved, the idea predicts that the homogametic sex will evolve counter strategies to win back or increase its control over offspring sex ratio, such as parental care or internal fertilisation. One important assumption of this hypothesis is that there are ecological situations that promote the conflict between the parents. If parents have no interaction with their offspring after spawning, e.g. in pelagic spawners, there would be no selection for sex chromosomes. We will conduct a phylogenetic study of evolution of heterogametic sex determination in fishes in relation to habitat, parental care and internal versus external fertilisation. Fish are ideal for testing this hypothesis since both parental care and sex chromosomes has evolved numerous times in this taxon. This project is important because it addresses the adaptive significance of sex chromosomes from the perspective of one of the most well respected and influential ideas about natural selection, namely Fisher's theory of the evolution of progeny sex ratios.











































































































































































































































































































































































































































































































































































































this is idtest: