Evolution of clasper morphology between Drosophila simulans and D. mauritiana. Maria D.S. Nunes¹, Kentaro Tanaka¹, Corinna Hopfen^2,3, Christian Schlötterer², Alistair P. McGregor¹. 1) BMS, Oxford Brookes University, Oxford, United Kingdom; 2) Institute for Population Genetics, Vetmeduni, Vienna, Austria; 3) Max Planck Institute for Biology of Ageing, Cologne, Germany.

   Male sexual characters are often among the first traits to diverge between closely related species. Identifying the genetic basis and evolutionary forces underlying this rapid evolution has great potential to allow us to understand the processes of animal diversification and the evolution of new species. Several traits of the genital arch have evolved in closely related species of Drosophila. In this study we focused on the evolution of the clasper, a structure important for correct positioning and attachment of the male to the female during mating. The size, shape and bristle number of this structure have evolved dramatically between D. mauritiana and D. simulans and it is likely to have affected their mating behavior. In order to map the genetic basis of these differences we generated a QTL map for clasper area and bristle number. We found two major QTL for clasper area, one on the right arm of the 2^nd chromosome and another on the right arm of the 3^rd chromosome, while clasper bristle number mapped to the X chromosome. Using marker-assisted recombination mapping, we have introgressed each of those QTL regions from D. mauritiana into D. simulans and used available gene expression data on male genital discs to identify candidate genes that cause these evolutionary changes . As well as studying how these genes cause variation in clasper morphology, since the clasper develops from the same tissue as other divergent terminalia structures, we are currently testing whether our candidate genes have pleitropic effects on anal plate and posterior lobe morphology. These results are important not only for understanding the genetic basis of genitalia evolution but also because they provide a platform for further research to test for differences in copulation behavior and isolation mechanisms between species.