Evolution of overwintering strategies in Eurasian species of the Drosophila obscura species group

The phylogenetic relationship of Eurasian species of the Drosophila obscura species group remains ambiguous in spite of intensive analyses based on mo rphology, allozymes and DNA sequences. The present analysis based on sequen ce data for cytochrome oxidase subunit I (COI), and alpha-glycerophosphate dehydrogenase (Gpdh) suggests that the phylogenetic position of D. alpina i s also ambiguous. These ambiguities hale been considered to be attributable to rapid phyletic radiation in this group at an early stage of its evoluti on. Overwintering strategics are diversified among these species: D. alpina and D. subsilvestris pass the winter in pupal diapause, D. bifasciata and D. obscura in reproductive diapause, and D. subobscura and D. guanche witho ut entering diapause. This diversity may also suggest rapid radiation at an early phase of adaptations to temperate climates. On the other hand, adult tolerance of cold was closely related to overwintering strategy and distri bution: D. obscura and D. bifasciata with reproductive diapause were very t olerant; D. alpina and D. subsilvestris, which pass the winter in pupal dia pause were less tolerant; D. subobscura having no diapause was moderately t olerant and D. guanche occurring in the Canary Islands was rather susceptib le. Tolerance of high temperature at the preimaginal stages seemed to be al so associated with overwintering strategy; i.e. lower in the species with p upal diapause than in those with reproductive diapause or without diapause mechanism. (C) 1999 The Linnean Society of London.