Variations of male cuticular hydrocarbons with geoclimatic variables: an adaptative mechanism in Drosophila melanogaster ?

7-tricosene (7T) and 7-pentacosene (7P) are the major components of cuticul ar hydrocarbons in Drosophila simulans and D. melanogaster males. A chemica l study of 16 isofemale lines of D. melanogaster sampled at the first and e ighth generations in laboratory conditions showed the stability of chromato graphical profiles. Then a large scale study of male 7T/7P polymorphism was performed with 85 populations of D. melanogaster and 29 of D. simulans col lected all over the world. There were significant correlations of the value s of the balanced ratio (7T - 7P)/(7T + 7P) with geo-climatic parameters, s uch as latitude, longitude, mean temperature, temperature range and vapour pressure. Parallel variations were also reported for the homologous linear alkanes (23 and 25 Carbon atoms) but not for the longer branched alkanes (2 7 and 29 Carbon atoms). No correlation was significant for the D. simulans populations studied. In this species a similar polymorphism of 7T/7P was fo und but restricted to a few populations from West Equatorial Africa.