Genetics of reproductive behaviour in Nasonia

Reproductive isolation is important in the process of speciation, but its genetic basis is poorly understood. To get more insight in this, I focused on three species from the Nasonia genus of parasitic wasps occurring in micro-sympatry in eastern North America. N. vitripennis is a cosmopolitan and generalist species that parasitizes pupae of several fly species. N. giraulti and N. oneida are specialists of pupae of blowflies commonly found in bird nests. In nature, the species are reproductively isolated by infection with species-specific strains of the bacterial endosymbiont Wolbachia that cause cytoplasmic incompatibility. In the area of sympatry, prezygotic isolation mechanisms are expected to have evolved that prevent hybridization. N. vitripennis and N. oneida females have strong mate discrimination (MD) against heterospecific males. N. giraulti females do not discriminate. It has been suggested that within-host-mating (WHM) in N. giraulti, where the other species mate after emergence from the host, functions as a reproductive barrier. I analysed the genetic architecture of interspecific MD and WHM using hybridization experiments, artificial selection and quantitative genetics. My results show that there is large variation in female interspecific MD between species pairs. The trait has a relatively simple genetic basis and lowered interspecific MD can be selected for in few generations. WHM occurs both in laboratory and field hosts in N. giraulti, but N. giraulti females do not mate inside hosts if an exit is available. I conclude that both interspecific mate discrimination and within-host-mating do not form a complete barrier to gene flow within this genus.