以粒線體DNA控制區序列探討台灣及南中國海海域泛熱帶斑海豚（Stenella attenuata）的族群結構

Population Genetic Structure of Pantropical Spotted Dolphin, Stenella attenuata, in Waters of Taiwan and South China Sea Based on Mitochondrial DNA Control Region Sequences

本研究是利用粒線體DNA控制區序列之447個鹼基探討台灣及南中國海海域泛熱帶斑海豚（Stenella attenuata）的族群結構與遺傳多樣性。我們將這些海域的海豚，區分為三個預設族群，包括台灣海峽、台灣東部海域與南中國海域，並且檢測此三海域的海豚族群並無族群分化之假說。在34個體的DNA序列中，共有14變異位點，可以分為13個單套型。在這些單套型中，有9個是地區特有型，包括台灣海峽2個、台灣東部海域4個與南中國海域3個。而南中國海域並無地區共有之單套型。遺傳多樣性估計值包含單套型多樣值（haplotype diversity, h）與核甘酸多樣值（nucleotide diversity,π）兩種，三個族群的數值範圍分別是h介於0.7778-0.8883，以南中國海域最高;π介於0.0049-0.0096，以台灣東部海域最高。與數種小型齒鯨同段DNA的遺傳多樣性估計值相比，本研究的估計值均偏低。由最小幅網路分析與親緣關係建構法分析三個族群之DNA單套型，均無明顯的區域性分化趨勢。分子變異分析結果發現，由單套型頻度資料所估算出的Wright’s fixation index, Fst，顯示南中國海族群分別與台灣海峽（Fst = 0.1761, p = 0.0156）以及台灣東部海域（Fst = 0.2029, p = 0.0059）兩個族群有顯著的分化。然而，由遺傳距離資料所估算的分化指數，Φst，任何族群間均無顯著分化。這是由於南中國族群之DNA單套型雖然具地區獨特性，但是其與台灣兩個族群大多數之單套型的相異度並不大所致。雖然有極多的族群研究顯示，棲地的差異是造成共域或鄰域之鯨豚族群分化的重要因素之一，然而由我們的研究結果顯示，位於亞洲大陸棚的台灣海峽淺水域與大陸斜坡陡降的台灣東部深水域的泛熱帶斑海豚族群，彼此之間並無顯著分化。未來的研究中，增加南中國海樣本數以及更系統性的在台灣海域蒐集樣本，將有助於釐清南中國海與台灣海域族群分化的問題，並且也可持續監測這些海域之海豚的遺傳多樣性，作為保育管理單位的建議。

A total of 447 base pairs of the mitochondrial DNA control region from 34 pantropical spotted dolphins, Stenella attenuata, in the waters of Taiwan and South China Sea were sequenced and analyzed. In this study, we tested the null hypothesis of non-differentiation genetic structure of the spotted dolphin of Taiwanese and adjacent waters. There were three putative populations in this study －Taiwan Strait, eastern Taiwan and South China Sea. The genetic structure and population differentiation of the putative populations were estimated to clarify the population status. There were 14 variable sites within the sequences and 13 haplotypes defined. Among the haplotypes, nine were unique and four were shared. The South China Sea population had three haplotypes, all of these were unique. The haplotype diversity estimates of the three populations range from 0.8883 in South China Sea, followed by 0.8182 in Taiwan Strait and 0.7778 in eastern Taiwan. Nucleotide diversity estimates range from 0.0096 in eastern Taiwan, 0.0078 in South China Sea and 0.0049 in Taiwan Strait. The Minimum-spanning network does not describe a clear pattern of haplotype and geographical locale relationship. Neighbor-joining and Maximum Likelihood phylogenetic analyses with Stenella longiroatris as outgroup also could not divide the haplotypes into clades representing the three putative populations. The Analysis of Molecular Variance (AMOVA) results show two patterns of population differentiation. The analysis using haplotype frequency, Fst, indicates significant population subdivision between South China Sea and Taiwan Strait (Fst = 0.1761, p = 0.0156), and between South China Sea and eastern Taiwan populations (Fst = 0.2029, p = 0.0059). However, the analysis using genetic distance and frequency information, Φst, does not reveal significant population differentiation between any pair of comparisons. Additionally, the relatively lower genetic diversity estimates of pantropical spotted dolphins in Taiwanese waters suggest that future monitoring is needed. A more systematic collecting method and expanding sampling area should be carried out for future investigations.