- 學位論文
台灣淡水沼蝦屬之地理親緣關係探討
Phylogeographies of the freshwater prawns (Macrobrachium Bate, 1868) of Taiwan
摘要
本研究利用台灣15種沼蝦(Macrobrachium Bate, 1868)的分子親緣關係，及在印度太平洋上的地理分布型態，來推論台灣沼蝦屬的生物地理起源及擴散路徑，並就其來台繁衍後在島上所形成的地理分群的關係作探討。 首先利用粒線體16S rDNA及核內28S rDNA序列，分別以貝葉氏、最大似然性、最大簡約性、最小演化及鄰近連接等分析方法，來建構其親緣關係樹。結果發現16S rDNA序列長度較短，含高量的腺嘌呤、低量的胞嘧啶及極顯著的transition。而序列間的歧異度及α-values均低，並伴隨著較高的transition/transversion (ts/tv)比值。使得物種間的遺傳距離小，親緣樹無法清楚分枝。相反地，28S序列則較長，含高量的鳥糞嘌呤及顯著的transversion。序列間的歧異度及α-values均較高，並具有較低的transition/transversion (ts/tv)比值。因此物種間的遺傳距離較廣，親緣樹分枝清楚。28S所建構的樹型，其解析度及信心支持率均明顯比16S所建構的樹型來得高。其中配合貝葉氏分析方法所建構的親緣關係樹，其解析度及信心支持率最高，在本研究中是最佳的分析模式。 台灣的淡水沼蝦，僅知1種為陸封型，其物種組成與菲律賓群島及琉球群島之相似度高。其起源及擴散路徑可分為4種類型：(1) 熱帶東南亞島群之東區：經由菲律賓群島來到台灣，包括M. australe、M. lar、M. latimanus、M. gracilirostre、M. jaroense、M. esculentum、M. lepidactyloides及M. placidulum等8種；(2) 熱帶東南亞島群之西區：經由菲律賓群島或中國大陸來到台灣，包括M. equidens、M. latidactylus及M. mammillodactylus等3種；上揭2類型共11個物種，皆為兩側洄游性，經由洋流來到台灣後，逐步適應環境，而生存在東部地區形成東岸分布型，它們主要分布在台灣東部，部分物種亦分布在鄰接的北部及南部地區，其中M. australe則另分布在台灣的西北部。這些物種在島上的分布及擴散來台的途徑與黑潮關係密切。(3)經由中國大陸來到台灣的陸封型M. asperulum、兼具兩側及陸封的M. nipponense 及兩側洄游的M. formosense；(4) 在台灣本島種化的M. japonicum及特有種M. shaoi；上揭2類型，除M. shaoi外，餘4種在島上分布形成全島型，它們廣泛分布於台灣的溪流，其中M. japonicum及M. formosense為兩側洄游性，其在島上的分布型態與兼具兩側洄游的M. nipponense及陸封性的M. asperulum極為相似，卻與同為兩側洄游性的全島型物種之分布極為不同，顯示M. japonicum及M. formosense或許並非全然為兩側洄游性，而是如M. nipponense為兼具兩側洄游性的物種，此點需要進一步的研究證實。台灣淡水沼蝦在島上的分布型態，是演化過程中物種地理起源、擴散來台途徑及其對環境適應能力等因素所造成。
並列摘要
This study used molecular phylogenies of 15 freshwater prawns (Macrobrachium Bate, 1868) of Taiwan and their distributions in the Indo-Pacific region to postulate their biogeographical origins and dispersal routes, and to relate them with their distribution patterns in Taiwan. For phylogenetic study, characters of mitochondrial 16S rDNA sequences (16S) and nuclear 28S rDNA sequences (28S) of the freshwater prawns of Taiwan were examined. The phylogenetic analyses were conducted with Bayesian (BI), maximum likelihood (ML), maximum parsimony (MP), and minimum evolution and neighbor-joining (MENJ) methods. The 16S extracted was smaller in sequence length, rich in adenine, poor in cytosine, and biased strongly to transitions in the nucleotide substitutions, whereas the 28S extracted was larger, rich in guanine, and biased to transversions. The phylogenetic trees derived from the 28S had appreciably higher topological resolution with deeper branching (less polytomies) and higher topological confidence with stronger phylogenetic signals than the 16S trees. The poor resolution and confidence of the 16S trees were attributable primarily to its poor sequence divergences associated with high transition/transversion (ts/tv) ratios and low α-values of the gamma distributions. The result was a severe convergence of taxa within a narrow range of small genetic distances, so that their bifurcation could not be determined unambiguously. The 28S was highly diverged and had larger genetic distances with low ts/tv ratios and high α-values, resulting in much less convergence of the taxa. The 28S tree reconstructed with BI produced the best topological resolution and confidence in the separate analyses. Therefore, the 28S with the BI method was selected for the phylogenetic analysis of this study. The freshwater Macrobrachium prawn fauna in Taiwan was diverse, rich in amphidromous species but poor in land-locked and endemic species. The fauna showed higher similarity to those of the Philippines islands and Ryukyu Islands than that of the China mainland. Their biogeographical origins and dispersal routes were postulated and divided into four groups: 1) the first group with its origin in the eastern region of tropical Southeast Asia islands, dispersing to Taiwan through the Philippines islands for M. australe, M. lar, M. latimanus, M. gracilirostre, M. jaroense, M. esculentum, M. lepidactyloides, and M. placidulum; 2) the second group with its origin in the western region of tropical Southeast Asia islands, dispersing to Taiwan through the Philippines and/or mainland China for M. equidens, M. latidactylus, and M. mammillodactylus; 3) the third group with its origin in mainland China for M. formosense, M. asperulum, and M. nipponense; and 4) the forth group with its origin on the island of Taiwan for M. japonicum. For the above four groups, the 11 species of the first two groups of the Southeast Asia origins were all amphidromous. They were distributed in the east-coast of Taiwan, some in its adjacent northern and southern regions. They were not found in the west coast. They showed a close association with the Kuroshio Current in the dispersion. For the four species of the last two groups of East Asia origins, they were common in streams around the island, and occurred in both east coast and west coast. M. japonicum and M. formosense that have been considered to be amphidromous showed the distribution patterns fairly similar to that of non-obligatory amphidromous M. nipponense and even to that of landlocked M. asperulum, rather than to those of the amphidromous species of the east-coast group. The evidences suggest that these two species might not be the amphidromous but the non-obligatory amphidromous. A further study is needed for the confirmation. The distribution patterns of the Macrobrachium prawns in Taiwan are resulted from their life cycle modes, adaptability to local environments at present and biogeographic origins and dispersal routes in the past evolutionary history. For the remaining species, M. shaoi is the only endemic prawn to Taiwan and its life cycle is still unknown.