The analyses of evolutionary factor and rate of marine organisms isolated in marine lakes, Palau Islands

虽然进行了许多研究，以澄清“海洋生物如何在海洋中进化？“，这是如此困难，因为广泛的基因流动发生在海洋中，如兔子鱼的情况（Kuriiwa等人，出版中）。然后，我们选择了帕劳群岛的部分混合型海洋湖泊作为演化模式。这些湖泊是由大约12，000年前硬珊瑚产生的石灰石上升而形成的，并且仍然以稳定的状态存在。如果湖泊被完全隔离，海洋生物就有可能在每个湖泊中被隔离和进化。湖中的动物群和植物群与外海的动物群和植物群有很大的不同。一些水母和藻类物种在形态和生态上与它们在外海的相关或相同物种不同。大部分物种的海洋湖泊种群遗传变异性极低，且各海洋湖泊种群与外海种群存在遗传分化。这表明，12,000年以来，海洋湖泊种群受到了强烈的瓶颈效应，并在各海洋湖泊中发生了独特的演化。为了与海洋湖泊物种的进化进行比较，我们还调查了帕劳群岛的陆生蜗牛。在每个岛上都发现了许多形态分化的陆生蜗牛物种。据认为，其中大多数是未描述的物种和特有的帕劳群岛。因此，可以得出结论，完全的地理隔离诱导生物进化较短的进化时间。

Although many studies were carried out to clarify "How do marine organisms evolve in the sea?", it was so difficult because extensive gene flow occurs in the sea, such as the case of rabbitfish (Kuriiwa et al., in press). Then, we selected meromictic marine lakes in Palau Islands as the evolutionary model. The lakes were formed by raise of lime stones derived from hard corals approximately 12,000 years ago and have still existed in stable state. If the lakes have been isolated completely, there is the possibility that marine organisms have been isolated and evolved in each lake.We investigated dominant species of fish, bivalves, copepods, jellyfish and algae in the lakes. The fauna and flora in the lakes are quite different from those of the outer sea. Some species of jellyfish and algae are morphologically and ecologically differentiated from their related or same species in the outer sea. Genetic variability of marine lake populations in most species is extremely low, and the each marine lake population was genetically differentiated from the outer sea populations. It suggests that the marine lake populations have suffered strong bottleneck effect and peculiarly evolved in each marine lake since 12,000 years ago. To compare with the evolution of marine lake species, land snails isolated in Palau Islands were also investigated. Many land snail species morphologically differentiated were discovered in each island. It is thought that the most of them were undescribed species and peculiarly speciated in Palau Islands. Thus, it is concluded that complete geographical isolation induces biological evolution for the shorter evolutionary time.