| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 106 === Freshwater fishes are ideal model species for studying phylogeographical patterns due to their limited dispersal capabilities and colonization histories. In the previous studies, vicariance events are often considered as the causes of population differentiation. However, this can not completely present the history of population differentiation, especially for differentiation of different species in different time. The mechanism of differentation in populations is still debating. Microphysogobio is a genus of small-sized freshwater fishes, belonging to the cyprinid subfamily Gobioninae distributed in East Asia. Twenty six species of Microphysogobio are considered valid in the world, and two species of which, M. alticorpus (MA) and M. brevirostris (MB) , are endemic to Taiwan. They are allopatrically distributed in, north and south of the Miaoli Plateau, respectively. In this study, I employed the mt cytb gene and eight nuclear genes as molecular markers to unravel the colonization and divergent histories of these two species. The results showed that there were different patterns of intraspecific differentiation in these two species. In MA, mt cytb revealed distinct lineages for samples collected from different localities. The nuclear genes, however, clearly showed gene flow between distinct mtDNA defined lineages. The mito-nuclear discordance may be caused by selection in mitochondrial genome. For conservation, evolutionarily significant units (ESU) should be rechecked. In MB, mtDNA and nuclear genes revealed two major lineages, and there may be population expansion in 0.14 million years ago. Different genetic basis of two lineages should be considered for conservation. The importance of this study is presenting molecular evidence of MA and MB were sympatric in Houlung river. Furthermore, the study suggested mitochondrial genome may not be neutral, and it may reveal signature of selection, which affected differentiation of populations.
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