東亞地區台灣吻鰕虎 (Rhinogobius formosanus) 之生活史及族群遺傳

Abstract

台灣吻鰕虎 (Rhinogobius formosanus) 長期被認為是台灣北部的特有洄游性物種，然而在2012年，於中國福建發現亦有其族群的存在。近期，兩個台灣的族群被研究且發現位於台北翡翠水庫上游的族群為陸封型族群。不過，對於中國的族群仍研究不足並且對該物種的生物地理模式的了解仍然有限。本研究主要為了探討兩個目的。首先，透過耳石的鍶鈣比分析探討中國的台灣吻鰕虎族群是否也存在陸封型族群。再來，透過台灣以及中國共五個族群的遺傳結構分析來探討造成族群分離的機制。本研究中所採樣的樣本供來自五個地區，其中兩個來自中國、三個包括一個陸封型族群來自北台灣。本研究所使用的分子標記為粒腺體DNA，用於分析五個台灣吻鰕虎族群的族群遺傳，而耳石的鍶鈣比分析則用於重建鰕虎的生活史。耳石的分析實驗結果顯示中國福清鰕虎的鍶鈣比為持續不間斷低走向的現象，判斷其為陸封型族群。另一方面，中國福鼎鰕虎的鍶鈣比則顯示出由高往低的走向，因此判斷其為洄游型族群。至於分子分析的結果，由分子變異分析 (AMOVA) 的結果來看，中國以及台灣兩邊的族群顯示出顯著性的遺傳差異。另外，中性檢定的結果顯示出台灣的兩個洄游型族群發生近期族群擴張的現象，而中國的族群則無，並且此現象由貝氏天際線來推測可能發生於冰河期結束後。雖然台灣吻鰕虎能在浮游階段進入到海洋，但是牠可能傾向於不活動至太遠處，進而避免了中國以及台灣族群間的基因交流。族群遷移分析的結果呈現台灣往中國的方向性，不過，從分子變異分析(AMOVA)以及遺傳分化程度(ФST) 的結果推測，地理隔離的效應較播遷的影響來得強。台灣洄游型的族群擴張現象可能因於時間尺度及環境的差別。總結來說，中國方面發現了一個陸封型族群，而中國及台灣的族群分離式由台灣海峽作為物理障蔽形成地理隔離所造成。

Rhinogobius formosanus is an amphidromous species of goby, which had been long considered endemic to northern Taiwan. However, a population was reported from Fujian, China in 2012. Recently, two populations in Taiwan were identified and a landlocked population at the upstream of the Feitsui Reservoir in Taipei was confirmed. Nevertheless, the populations in China were still being understudied and the knowledge of the biogeographic pattern of this species is still limited. There are two objectives in this study. First, to investigate as to whether there is a landlocked population of the R. formosanus in China by analyzing the otolith Sr:Ca ratios. Second, to examine the mechanism that causes the disjunction of R. formosanus in Taiwan and China by comparing the genetic structure among the five populations. In this study, the samples were collected from five locations, two from Fujian, China and three from northern Taiwan, including one landlocked habitat. Mitochondrial DNA was used as the molecular marker to study the population genetics of the five R. formosanus populations, while the otolith Sr:Ca ratios were used to reconstruct the life history of the gobies. The results showed a consistently low Sr:Ca ratios in the gobies from Fuqing in China, suggesting the Fuqing population being a landlocked goby. On the other hand, the gobies from Fuding, China showed a high to low Sr:Ca ratios, suggesting the Fuding population being amphidromous gobies. As for the molecular analysis results, the populations between Taiwan and China showed a significant genetic differentiation based on the AMOVA analysis result. Besides, the two amphidromous populations in Taiwan showed a recent population expansion based on the neutrality test result, but not the China populations and the Bayesian skyline result suggested it happened at the end of glaciation. Although R. formosanus can enter the ocean during the larval stage, it might not travel for a long distance, which can prevent the gene flow between the Taiwan and China populations. The population migration result showed a direction of Taiwan to China, however, the AMOVA and ФST results suggested the vicariance effect stronger than dispersal. The results of population expansion happened in Taiwan’s amphidromous populations might be due to the time scale and environmental differences. In conclusion, a landlocked population is found in China and the disjunction of the China and Taiwan populations is caused by a vicariance in which the Taiwan Strait formed a barrier that separated the populations.