Studying latitudinal variations of winter related gene and characters in Drosophila simulans populations

Clines that are seen in allele frequency and quantitative characters are accepted as evidence of adaptive evolution. Studying the clinal variations is the key of understanding local adaptation. The high adaptation ability of cosmopolitan species enables them to be colonized in different climatic and geographical locations. Latitudinal clines that are seen in cosmopolitan species which spread over wider range of habitats put these species at the center of adaptive evolution studies. Drosophila simulans, which is a cosmopolitan species, is not as popular as Drosophila melanogaster for local adaptation studies, therefore knowledge about the adaptation mechanisms of this species is limited. There are different theories about how D. simulans overwintering. In this thesis, populations that were collected from different latitudes - Kampala, Haifa, Hatay, Ankara and Napoli - were studied in order to understand winter adaptation. For this purpose, we examined the frequency of reproductive diapause, chill coma recovery time and dry body weight characters which were associated with overwintering and the "Insulin like receptor" (InR) gene that was able to associated with these characters in D. melanogaster. Previous studies also showed clinal variation in these characters and overwintering in D. melanogaster. According to the results, populations differentiated in terms of phenotypic characters and InR locus, and inter-population variation was found to be related with latitude. In addition, we showed that D. simulans is under the same selection pressure for two characters in different geographical regions; and these results provide strong evidence for parallel clines for the first time for this species. Results shows that these characters and the InR locus may play a role in the local adaptation of the D. simulans populations for overwintering in their local environment, and thus our study supports the theory that the populations can overwinter in their local region without migration.