The analysis of factors limiting the distributions of drosophilid flies

果蝇主要出现在从热带到北极地区的林地。但单一种的分布范围不大，热带种的分布几乎局限于热带地区，温带种的分布几乎局限于温带地区。这项研究的重点是为什么热带物种不分布在温带地区，而温带物种不存在于热带地区。根据目前对来自日本的30种果蝇的研究，热带物种不耐寒，这阻碍了它们在温带地区的定居。据报道，在许多生物体中，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，在果蝇身上没有观察到这种趋势。另一方面，在较温暖的地区缺乏耐寒物种表明，耐冷性的获得导致了对较温暖地区的适应性的丧失。在这里，比较了28种果蝇的行走速度和蛹发育率。如果行走速度减慢，它们就会变得容易受到捕食者的攻击。如果蛹发育速度减慢(即蛹期延长)，它们也会容易受到捕食者、寄生蜂和感染性微生物的攻击。在我们的实验中，耐寒物种的行走速度和蛹发育速度都较慢，这表明耐寒物种在较温暖的地区比不耐寒物种更不利。然而，对捕食者、寄生蜂或果蝇的感染性微生物知之甚少。本研究对日本果蝇寄生蜂进行了调查，共记录约20种。需要研究耐寒物种是否比不耐冷物种更容易受到寄生蜂的攻击。

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.