Molecular Genetic Analysis of a Seasonal Character in D. melanogaster Natural Populations

D. melanogaster has Afrotropical origins, colonising Europe around 10-15 thousand years ago, where they faced the challenges of a variable, seasonal environment. Individuals able to predict oncoming unfavourable winter conditions were at a selective advantage. This may have led to the evolution of seasonal diapause, a physiological response allowing flies to overwinter. In this work I studied the adaptation of the D. melanogaster overwintering strategy to different environmental conditions. Several genes have been found to modulate diapause, and some of these are characterised by two (or more) alleles whose frequencies are distributed as latitudinal clines in North America and Australia. We have studied the geographical distribution of the allele frequencies of three genes (timeless, tim; couch potato, cpo and Insulin-like-Receptor, InR) in European natural populations of D. melanogaster. Overall, our results highlight a peculiar and complex situation in Europe, as compared to North America or Australia where significant and robust clines were found for cpo and InR. Interestingly, such geographical differences correlate with the phenotype: clines in diapause are robust in North America but extremely weak in Europe, perhaps reflecting different selective pressures and colonisation dynamics in the Old World.