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

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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.