Origin and Evolution of temperate Drosophila

温带果蝇被认为起源于热带或亚热带。目前的研究表明，真菌和草食动物有利于在温带地区定居。在以水果为食的黑腹果蝇物种群中，takahashi亚群和montium亚群的一些成员成功地在温带地区定居。目前的分子系统发育研究表明，montium亚群的温带成员至少起源于亚热带高原。温带和亚热带高原物种能够在较低的温度下生长。这种能力可能是在温带地区定居的预适应。而亚热带高原种的滞育和耐寒性不如亚热带低地种。因此，认为亚热带高原物种需要大量的遗传变化来适应温带气候。温带物种滞育是控制生命周期和获得耐寒性的关键。目前的结果表明，滞育对获得对微生物的抗性很重要。这些温带物种大多是多伏特的，在秋季白天很短就进入滞育。另一方面，D.alpina和D.moriwakii是单伏性的，滞育期除短日滞育外，还有长日滞育。由于它们的滞育时间较短，因此它们的祖先被认为是多伏特的，通过获得长时间的滞育而变成单伏特的。

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.