由於東南亞擁有複雜的地質歷史及海洋環境，因此生物多樣性尤其豐富。在更新世時期(Pleistocene)，海平面波動導致淺水域的陸地暴露, 繼而造成海洋盆地的分隔。在末次盛冰期(Last Glacial Maximum)，最低海平面甚至低於現今的水平120米。當時大量的土地暴露於海平面上，最大的連接加里曼丹（婆羅洲），蘇門答臘和爪哇，稱為巽他陸架(Sunda Shelf)。巽他陸架不單隔開了南中國海，西里伯斯海和蘇祿海，更分隔了印度洋和太平洋。當海平面上升，巽他陸架逐漸被海水覆蓋，附近的海洋生物於是重新佔領為淒息地。因此物種的散播和混合相信是造成東南亞地區豐富生物多樣性的原因。 / 親緣地理研究顯示，巽他陸架的出現顯著地塑造了海洋動物的基因格局(genetic pattern)。其中最突出的，是在印尼東部（西里伯斯海和弗洛雷斯海）和印尼西部（爪哇海）的動物樣本發現了明顯的基因分別。另一方面，由於海洋動物大部分都有浮游幼蟲階段，促進了遺傳的連繫(genetic connectivity)。然而，大部份的親緣地理研究都針對海洋動物，而缺乏對其他生物（例如植物及藻類）的知識。廣泛分佈於東南亞沿海海域的大型藻類馬尾藻屬(Sargassum spp.) ，有著獨特的生命史。它們有著固定的繁殖幼體(germlings)，而那些繁殖幼體卻可以依附在浮藻體(drifting fronds)上經海流傳播。這特點使它們成為一個很好的研究對象，並提供不同的視角了解該地區的親緣地理學和進化史。本論文選擇了三種在本地區最常見和分佈最廣的品種作研究，分別為匍枝馬尾藻(S. polycystum)，硬葉馬尾藻(S. aquifolium)和冬青葉馬尾藻(S. ilicifolium)。這些物種的種群結構預計會同時受到過去的地理隔離(vicariance event)和現今的海洋環流的影響。因此本研究用了三個分子標記，分別為細胞核內第二內轉錄間隔區(ITS2)，葉綠體染色體內的雙磷酸核酮糖羧化脢大小單位的間隔序列區(RuBisCo spacer)和線粒體細胞色素c氧化酶亞基-III(cytochrome oxidase subunit-III)來分析它們的種群結構。 / 研究揭示了冬青葉馬尾藻(S. ilicifolium)的種群可分為四個分支：西爪哇，南中國海，西里伯斯海/弗洛雷斯海和澳大利亞/太平洋群島，這相信是過去冰川分離的結果。這些分支重新佔領巽他陸架地區後產生了單型(haplotype)的混合。相反，匍枝馬尾藻(S. polycystum)和硬葉馬尾藻(S. aquifolium)在基因上比較同質並找不到分支。它們種群結構上的差異是由於不同的繁殖方式：冬青葉馬尾藻(S. ilicifolium)是季節性繁殖的，所以它的傳播很依賴於季候風洋流的方向；然而硬葉馬尾藻(S. aquifolium)則可以全年繁殖，這特性促進了它的傳播和基因的連繫；最後，匍枝馬尾藻(S. polycystum)能夠無性繁殖，這解釋到它相對較低的遺傳多樣性(genetic diversity)。 / 此研究首次透過東南亞馬尾藻的比較親緣地理發現不同的繁殖方式造成了種群結構的差異，並藉此提供了另一種機制來解釋該地區的進化歷史。 / Southeast Asia is well-known for its high biodiversity which is largely due to its complex geological history and present day oceanographic conditions. Fluctuating sea level during the Pleistocene resulted in exposure of land masses in relatively shallow water and isolation of marine basins. The lowest sea level at Last Glacial Maximum was 120m below present day level. This exposed a large land mass known as the Sunda Shelf which connected Kalimantan (Borneo), Sumatra and Java. South China Sea, Celebes Sea and Sulu Sea were isolated from each other while Indian Ocean was separated from Pacific Ocean. After rising of sea level, recolonization to Sunda Shelf region occurred. Population dispersal and mixing may have contributed to cause high biodiversity in the region. / Previous phylogeographical studies revealed significant genetic pattern of marine animals shaped by the emergence of Sunda Shelf. The most prominent of these was the isolation between Eastern (Celebes Sea and Flores Sea) and Western Indonesia (Java Sea). On the other hand, present oceanographic conditions also facilitated genetic connectivity among marine animals as most of them have pelagic larval stages. Most of the phylogeographical studies, however, were on marine animals. Marine macroalgae, in particular members of the genus Sargassum, are widely distributed in the coastal seas of Southeast Asia. Their unique life history patterns and restricted dispersal ability due to their immobile germlings on one hand, and unique dispersal strategy on the other hand with germlings attached on floating fronds that can be drifted by ocean currents, make them a good candidate to provide a different perspective in understanding the phylogeography and the evolutionary history of the region. Three species of Sargassum, S. polycystum, S. aquifolium and S. ilicifolium were chosen for study. They are the most common and most widely distributed canopy species in Southeast Asia. The population structures of these species were expected to be subjected to the influence of both the vicariant events in the past and the present day oceanographic circulation. Three molecular markers were used to assess the presence of any population structure, namely the nuclear Internal Transcribed Spacer 2 (ITS2), plastidal RuBisCo spacer (Rbc spacer) and mitochondrial cytochrome oxidase subunit-III (Cox3). / Significant structure was revealed in populations of S. ilicifolium, which could be divided into four clades: West Java, South China Sea, Celebes/Flores Sea and Australia/Pacific Islands as the result of past glacial isolation. Recolonization to Sunda Shelf occurred with admixture of haplotypes from adjacent clades. In constrast, homogeneous population was revealed in S. polycystum and in Southeast Asian population of S. aquifolium. The difference in population structure between these three species may be explained by differences in their modes of reproduction. Sargassum ilicifolium exhibits seasonal reproduction and its dispersal was highly dependent on direction of monsoon currents. On the other hand, S. aquifolium reproduces throughout the whole year which may facilitate its dispersal and genetic connectivity within Southeast Asia. Finally, S. polycystum can propagate asexually. This could have contributed to its low genetic diversity across its wide distribution range. / The present research provided the first comprehensive examination of comparative phylogeography of macroalgae in Southeast Asia with mode of reproduction found to be an important factor that significantly contributed to the structure of Sargassum populations. This study thus provided another likely mechanism to explain the evolutionary history of the region, as exemplified by the large genus Sargassum. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Chan, Sze Wai. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 126-138). / Abstracts also in Chinese.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077702 |
| Date | January 2014 |
| Contributors | Chan, Sze Wai (author.), Ang, Put O. (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Life Sciences, (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (xiv, 138 leaves) : illustrations (some color), maps (some color), computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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