The analysis of factors limiting the distributions of drosophilid flies

果蝇主要分布在热带至北极地区的林地。但单种分布范围不太广，热带种的分布几乎局限于热带地区，温带种的分布则局限于温带地区。本研究主要探讨热带物种为何不在温带地区分布，温带物种为何不在热带地区存在的问题。根据对日本30种果蝇的研究，热带果蝇不耐冷，这抑制了它们在温带地区的定居。据报道，在许多生物中，适应寒冷的物种比来自温暖地区的物种具有更高的代谢率。然而，在果蝇中没有观察到这种趋势。另一方面，温暖地区耐寒物种的缺失表明耐寒性的获得导致了对温暖地区适应性的丧失。本研究比较了28种果蝇的行走速度和蛹发育速度。如果行走速度降低，它们就容易受到捕食者的攻击。如果蛹发育速度减慢（即蛹期延长），它们也容易受到捕食者、拟寄生虫和传染性微生物的攻击。在我们的实验中，耐寒物种的行走速度和蛹发育速度较低，表明耐寒物种比不耐寒物种在温暖地区更不利。然而，对果蝇的捕食者、拟寄生物或感染性微生物的研究却知之甚少。本研究对日本果蝇的拟寄生蜂进行了调查，记录了20余种。需要研究耐寒品种是否比不耐寒品种受到的寄生蜂攻击更严重。

Drosophilid flies occur mainly in woodlands from tropical to arctic regions. However, the distribution rage of single species is not so wide, and the distribution of tropical species is almost restricted in tropical regions and that of temperate species in temperate regions. This study focuses on the question why tropical species are not distributed in temperate regions and temperate species are not present in tropical regions. According to the present study with 30 drosophilid species from Japan, tropical species are not cold tolerant, and this inhibits them to colonize temperate regions. It has been reported in many organisms that cold-adapted species have higher metabolic rates than species from warmer regions. However, such tendency was not observed in drosophilid flies. On the other hand, the absence of cold-tolerant species in warmer regions suggests that the acquisition of cold tolerance resulted in the loss of adaptability to warmer regions. Here, walking speed and the rate of pupal development were compared for 28 drosophilid species. If walking speed is reduced, they would become vulnerable to predators. If the rate of pupal development is retarded (i.e., pupal period is prolonged), they would also become vulnerable to predators, parasitoids and infectious microorganisms. In our experiments, cold-tolerant species had lower walking speed and lower rate of pupal development, suggesting that cold-tolerant species are disadvantageous in warmer regions than cold-intolerant species. However, little is known on predators, parasitoids or infectious microorganisms of drosophilids. In this study, we made a survey on parasitoid wasps of drosophilid flies in Japan and recorded about 20 species. It is needed to examine whether or not cold-tolerant species are more heavily attacked by parasitoids than cold-intolerant species.