Sex role dynamics in gobies: ultimate and proximate control

Traditionally, animals have been considered to have rather unflexible and 'conventional' sex roles: males compete for access to females by courtship and aggression; females are more coy and choosy. However, recent theory suggests that sex roles may vary a ccording to mate availability (operational sex ratio, OSR) and sex specific breeding costs. This theory has already had some success in explaining sex role differences between species. However, the control and magnitude of within species variation in sex roles are poorly understood. We have recently found that the two-spotted goby (Gobiusculus flavescens), a small marine fish, switch sex roles during their short breeding season: males are competitive early on, females late. This coincides with a dramatic change in OSR over the season and provides the first demonstration of a temporal sex role reversal in a vertebrate. In the present project, we investigate what are the major determinant(s) of animal sex roles. Specifically, we test if mating competition a nd choosiness in mate choice are influenced by OSR and breeding costs (parental investment). The project includes international collaboration between theoretical and empiricial experts, and addresses both ultimate and proximate aspects of sex roles. It is likely to significantly improve our understanding of animal sex role dynamics and sexual selection.