STUDY ON DISRUPTIVE SELECTION CAUSEING SPECIATION IN COMPLEX PREDATOR-PREY SYSTEMS

从行为学的角度研究了自然界中形成复杂捕食-食饵系统的因素。首先对目标种的系统发育进行了分析，发现目标种是单系的。其次是实验条件下几种猎物和捕食者的行为特征。例如，长裂叶螨（Schizotetranychus longus Saito）的大而连续的巢的功能有利于许多成虫在很长一段时间内集中进行合作防御，尽管它们的巢因其大而相对容易受到掠食性入侵。另一方面，由一只白裂叶螨雌性反复建造的较小的、分散的巢穴（最多有10个卵）是坚固的避难所，可以防止几个捕食者物种的入侵。除了上述功能外，我们还发现，一旦分散的巢穴遭受捕食，它们就会成为欺骗捕食者的“假人”。此外，它们在发现巢穴后，大多会侵入巢穴寻找并捕食卵。也就是说，这些分散的空洞巢穴增加了捕食者的搜索成本（时间），在遭受捕食后起到了“欺骗捕食者的假人”的作用。因此，我们可以得出这样的结论：这种捕食压力可能是一种破坏性的选择压力，导致了celarius种群的形成。在小甲虫和蚂蚁中，我们也发现了一些相关的现象，并确定了它们的系统发育。这些结果已编制为13份报告，其中4份报告已被接受或出版。其他9个目前正在提交。因此，本研究结果强烈表明，具有多种特征的多个捕食者的捕食压力有时是通过破坏性选择导致猎物物种形成的非常强大的因素。

We studied on the factors which caused complex predator-prey systems in the nature from several behavioral view points. First we analyzed the phylogenies of the target species focused on and revealed that the species concerned are monophyletic. Next the behavioral traits of several prey and predator species under experimental conditions. For example, the function of the large and continuous nests of Schizotetranychus longus Saito was beneficial to cooperative defense through the concentration of many adults over a long period, although the nests are relatively vulnerable to predatory intrusion because of their large sizes. On the other hand, the smaller, scattered nests (with at most ten eggs) constructed repeatedly by a single Schizotetranychus celarius Banks female were solid refuges that can prevent several predator species from intruding. In addition to the above function, we found that once scattered nests have suffered predation, they then function as "dummies" to delude predators. Furthermore, most of them should invade the nests to search for and feed on eggs after nest detection. Namely, we indicated that these scattered void nests increase a predators searching cost (time), then function as "dummies for deluding predators" after suffering predation. Therefore, we could conclude that such predation pressure might operate as a disruptive selection pressure which caused the speciation of the celarius species group. In small beetles and ants, we also revealed several related phenomena and determined the phylogeny of them. These results have been prepared as 13 reports of which 4 reports had been accepted or published. The other 9 are now under submission.Then, the present results strongly suggest that the predation pressure by multiple predators having various traits sometimes operate as very strong factors which cause the speciation of prey species through disruptive selection.