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

尽管进行了许多研究来澄清“海洋生物是如何在海洋中进化的？”，但这是非常困难的，因为海洋中存在广泛的基因流动，例如兔子鱼(Kuriwa等人，正在出版中)。然后，我们选择了帕劳群岛的分生海相湖泊作为演化模式。这些湖泊是大约12000年前从硬珊瑚中提取的石灰石抬升形成的，至今仍以稳定的状态存在。如果这些湖泊已经被完全隔离，那么每个湖泊中的海洋生物都有可能被隔离和进化。我们调查了湖泊中的鱼类、双壳类、桡足类、水母和藻类的优势物种。湖中的动植物与外海的有很大的不同。一些种类的水母和藻类在形态和生态上与它们在外海的近亲或相同物种有所不同。海洋湖泊种群在大多数物种中的遗传变异性极低，每个海洋湖泊种群都与外海种群存在遗传分化。这表明，自12000年前以来，海洋湖泊种群遭受了强烈的瓶颈效应，并在每个海洋湖泊中发生了独特的演化。为了与海洋湖泊物种的演化进行比较，还调查了帕劳群岛分离的陆地蜗牛。在每个岛屿上都发现了许多形态分化的陆生蜗牛物种。据认为，它们中的大多数是未被描述的物种，并在帕劳群岛特有的物种。因此，完全的地理隔离导致生物进化的时间更短。

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.