Systematics of Seychellean Caecilians (Amphibia:Gymnophiona)

本研究旨在研究西印度洋塞舌尔群岛几个种群和无尾动物物种之间的进化关系。无足动物是一种小型无腿的穴居两栖动物，主要生活在热带地区。塞舌尔的花岗岩岛屿是部分被淹没的微大陆的山顶残余物。大约18000年前，当世界海平面较低时，塞舌尔微大陆（129560平方公里）完全出现。随着冰川后地球变暖，海平面上升，大约1万年前，塞舌尔微大陆分裂成一个群岛。与此同时，出现在微大陆上的物种被分散成岛屿种群。由于碎片化，在这些岛屿种群之间没有基因流动（杂交），如无尾鳗，它们不耐海水，缺乏跨越海洋屏障的传播手段。物种范围的破碎化是平行发生的，因此几个物种具有相同的破碎化历史。上述情况非常适合于研究各种进化现象。研究的主要目标是：(1)通过比较解剖和生化特征来确定物种和种群的进化关系；(2)确定基因交换中断对种群分化的影响；(3)对比解剖分化，确定岛分离时间与分子分化的关系；(4)确定不同物种间的遗传分化模式是否相似，这表明进化速度是一致的；(5)利用物种间不同程度分散的多物种方法检验最近发展起来的基因流动模型。

The research is aimed at studying the evolutionary relationships among several populations and species of caecilians in the Seychelles Archipelago, western Indian Ocean. Caecilians are small, legless, largely burrowing amphibians restricted to the tropics. The granitic islands of the Seychelles are the mountaintop remnants of a partially submerged microcontinent. About 18,000 years ago when world sea-levels were lower, the Seychellean microcontinent (129,560 km2) was fully emergent. With postglacial warming of the earth, sea-levels rose, and, about 10,000 years ago, the Seychellean microcontinent was fragmented into an archipelago. At the same time, the species that occurred on the microcontinent were fragmented into island populations. Since fragmentation, there has been no gene flow (interbreeding) between these island populations in species like caecilians, which are intolerant of salt water and lack means of dispersal across marine barriers. The fragmentation of species' ranges occurred in parallel, so that several species share the same fragmentation history. The situation described above is well-suited for the study of a variety of evolutionary phenomena. The major goals of the research are to (1) determine the evolutionary relationships of the species and populations by comparing anatomical and biochemical characters; (2) determine the influence of interrupted gene exchange on the divergence of populations; (3) determine the relationship between island separation time and molecular divergence compared to anatomical divergence; (4)determine whether patterns of genetic divergence are similar across species suggesting uniform rates of evolution; and (5) test recently developed models of gene flow using a multispecies approach with different degrees of dispersibility among species.