| Summary: | 博士 === 國立臺灣師範大學 === 生命科學研究所 === 95 === The colonization and differentiation of mangrove species are noticeably affected by geographic histories. The Indo-West Pacific (IWP) is the region that contains the most abundant and specious mangrove assemblages. The population of Ceriops tagal endemic in Southeast Asia, like that of many other mangrove species, was structured by the isolation of present Malay Peninsula and ancient Sundaland. I used maternally inherited chloroplast DNA, with which the effects of pollen dispersal could be excluded, to retrace the phylogeographic relationships among populations and dispersal route of propagules of C. tagal. In this dissertation, the Malay Peninsula was demonstrated to effectively isolate the gene flow of populations of C. tagal between the South China Sea (SCS) and the Bay of Bengal (BOB). During the glacials, the emergence of the Sunda Shelf connected the Borneo and the Malay Peninsula, forming a strict barrier named Sundaland. This caused populations within the SCS sharing common ancestral genotypes, and so was the situation in populations of the BOB water mass. The Gulf of Thailand (GOT) began to take shape 21 thousand years ago, and mangroves therefore started to retreat (or expand) to the coasts of the GOT. While populations in the GOT had frequent gene flow due to the tides and seashore currents, the independent demographic dynamics of each local population structured the whole GOT population. The closed gulf maintains the stable historical demography of whole GOT population and thus forms a classical metapopulation. The Kra Isthmus, the narrowest part of the Malay Peninsula, had been submerged under sea level before ca. 5 Mya, and this might lead to unhindered gene flow of mangroves between the SCS and the BOB. The divergent time of the SCS and BOB populations based on strict molecular clock is slightly underestimated when compared with the formation time of the Kra Isthmus. The long distance dispersal between the SCS and the BOB may be the cause of the underestimation of molecular clock. The most likely route for long distance dispersal across the land barrier is that via the Malacca Strait. The high gene flow between populations in the South Malay Peninsula and other areas in the past estimated by the coalescent-method provides an indirect evidence of Malacca Strait as the gate of dispersal. The isolation of populations in the two water masses during the glacials and the acceleration of gene flow due to sea-level rise during the interglacials might cause the high genetic diversity of mangroves in the IWP now. Moreover, while the periodic expansion and contraction of the SCS due to the sink and emergence of the Sundaland caused population expansion in the SCS, this situation never happened in the BOB, and population there maintained demographically stable. The population in the SCS may expand through colonization instead of local population growth because only few local populations were detected to expand. Thus, for conservation application, I suggest that the coasts of the Southeast Asia should be protected in order to provide steppingstone for the dispersal of mangroves.
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