| Summary: | 碩士 === 東海大學 === 生物學系 === 91 === Anourosorex squamipes, which is the monotypic species in the genus Anourosorex, is distributed from Tonkin, through Burma to Szechuan, China and Taiwan, showing a disjunct distribution pattern. The Taiwanese form was described as a subspecies A. squamipes yamashinai and occurs in the mountainous areas of Taiwan. The purpose of my study is to investigate the genetic variation within Taiwan population and compare the divergence with disjunct population in Mainland China. Moreover, I will try to explain the possible process and divergence time that caused the isolation.
Liver tissues were obtained from 78 individuals who were collected at 19 localities in Taiwan. Those of 8 individuals from Nan-Chung city and 2 individuals from Main-Yang City in Szechuan province were prepared also. The cytochrome b fragment was amplified using PCR with two primers designed newly. The partial sequences (737 bp) of all specimens from Southwestern China and Taiwan were successfully determined. The complete sequences (1140 bp) of cytochrome b gene were also determined from 5 specimens of Mt. Houhuan in Taiwan and 2 specimens of Main-Yang City in Szechuan province. Those complete sequences were used to explain the evolutionary relationship between two populations of Taiwan and Southwestern China. In a result of phylogenetic analysis of partial sequences, 28 haplotypes were identified with 43 variable sites of Taiwan population. The results of phylogenetic trees were indicating that Taiwan population distinctly diverged from Southwestern China population and 28 haplotypes in Taiwan were clustered into two groups (Northern and Southern groups). In addition, there were 7 diagnostic sites could be used to distinguish both groups of Taiwan. The genetic distances between Northern group in Taiwan and Southwestern China population was almost similar to that between Southern group in Taiwan and Southwestern China population. Furthermore, the haplotype diversity (h) and fixation index (FST) were revealed that the divergence would be significantly high within Taiwan population. This result was supported by AMOVA test also.
In a result of analysis of complete cytochrome b gene sequences, an intraspecies variation (6%) was indicated from the genetic distance between Taiwan and Southwestern China population. Analysis of divergence time based on molecular clock theory was revealed that Taiwan and Southwestern China population was separated at 0.72 Mya and the two groups of Taiwan population were separated at 0.19 Mya. From these data, the invasion of A. squamipes from continent to Taiwan might have been occurred once. The population of A. squamipes might have reached at the western area of Taiwan during the Günz glacial period and then been distributed into Taiwan. After glacial period, the population could have been reduced, and took refuge to the middle-elevation of mountainous area, with the "bottleneck effect". So, the two groups could have been isolated by topography of Taiwan and evolved independently.
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