| Summary: | 博士 === 國立清華大學 === 生命科學系 === 97 === The genus Formosania is distributed in mountain streams in Taiwan and in south-eastern coast rivers of China. Their limited dispersal ability, the needs of high contents of dissolved oxygen in freshwater, and being considered economic invaluable make them appropriate materials for study of the biogeography across Taiwan Strait. We collected Formosania spp. samples from central-western to north-eastern Taiwan, and south-eastern rivers (from Pearl R. to Fei-Yun R.) in China. F. stigmata is the most widely distributed species in geography, it is found in Jiao-Xi R., Min-Jiang R., and Han-Jiang R.; F. lacustre is not only found in Taiwan, but also in Mu-Lan R., Jing-Jiang R. in China; F. fascicauda is found only in Jiou-Long R., which is different from previous records. We sequenced Cyt b gene, followed by Neighbor Joining tree analysis, and Nested Clade Analysis. We found that F. lacustre was closely related to F. fascicauda, and then F. stigmata. F. chenyiyui, however, was closely related to Vanmanenia, the genus most related to Formosania. By molecular dating and geographical events referring, we speculated the time and migration pattern of the genus Formosania: the ancestors of Formosania might originate in Yangtze R., nearly 9 million years ago they migrated to the south-eastern coast area of China; around 4 million years ago, in eastern Min-Jinag R. drainage, the ancestors of F. stigmata formed. Meanwhile, in Jin-Jiang R. and Jiou-Long R., the ancestors of F. lacustre and F. fascicauda formed. About 1.5 million years ago, the population in Jiou-Long R. separated from that of Jin-Jiang R., F. fascicauda appeared. Between 1.4-1.2 million years ago, the headwater stream of eastern Min-Jiang R. captured the western Min R., the F. stigmata in eastern Min R. followed the connected river systems to Han-Jiang R.. In latest glacial age, F. stigmata migrated from Min-Jiang R. to Jiao-Xi R.. The Formosania sp. population in Mu-Lan R. was previously classified as F. fascicauda or F. stigmata, but the Cyt b gene analysis and morphological comparison indicated a strong similarity of this population to F. lacustre. We speculate that the population in Mu-Lan R. was formed in the latest ice age when F. lacustre dispersed from Taiwan to Fujian coastal region, remained in Fujian during the interglacial period.
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