Origin and Evolution of temperate Drosophila

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Temperate drosophilids have been assumed to have originated from tropics or subtropics. The present study suggests that fungus-and herbage-feeders are advantageous to colonize temperate regions. In the Drosophila melanogaster species group of which members are fruit-feeders, some members of the takahashii and montium subgroups have succeeded to colonize temperate regions. The present molecular phylogenetic study suggests that at least the temperate members of the montium subgroup have originated from subtropical highlands. The temperate and subtropical highland species were able to grow at moderately low temperatures. This ability may be preadaptation to colonize temperate regions. However, the subtropical highland species did not have diapause and coldtolerance as well as the subtropical lowland species. Therefore, it is considered that a large genetic changes are required for the subtropical highland species to adapt to temperate climates. Diapause of temperate species is known to be critical to control life cycles and acquire cold tolerance. The present result suggests that diapause is important to acquire resistance to microorganisms. Most of these temperate species are multivoltine and enter diapause at short daylengths in autumn. On the other hand, D.alpina and D.moriwakii were univoltine and had long-day diapause in addition to short-day diapause. Since they have short-day diapause, their ancestors are assumed to be multivoltine and become univoltine through acquisition of long-day diapause.