Formation of reproductive barriers in a hybrid zone of American and Caribbean Drosophila melanogaster. Joyce Kao, Sergey Nuzhdin. University of Southern California, Los Angeles, CA.

   In order to understand the interaction between gene flow and adaptation in Drosophila melanogaster, multiple populations have been collected from different locations along the southeast US and the Carribean Islands. We specifically focus on studying the existence of reproductive barriers in populations collected from regions where two allopatric populations interbreed again after being separated for a long period of time by which each individual population has accumulated new alleles adapting to their separate environments. The southeast US and the Carribean Islands are a recent hybrid zone between two distinct populations that diverged 10000 years ago: the European flies which colonized the US with the European settlers and the African flies which were introduced into the Caribbean islands via the trans-Atlantic slave trade. Previous studies have already established the existence of clines in several pre-zygotic/pre-mating reproductive characteristics in flies out of this area. We have phenotyped post-mating traits in female flies including re-mating rates, egg laying rates, and post-mating lifespan and have found evidence that some of these traits may be post-mating reproductive barriers. We also have evidence that partial temporal isolation might be occurring in this cline. Genome-wide signatures of selection especially in genes relating to pre- and post-mating reproductive barriers will be examined by re-sequencing 23 isofemale lines from this area of the world.