台灣東部地區草蜥屬雜交現象之偵測

Abstract

台灣草蜥（Takydromus formosanus Boulenger 1894）包含了兩個尚未發表的隱蔽種，其一為翠斑草蜥（學名暫定為Takydromus viridipunctatus），分佈在台灣的北部地區，並以立霧溪的北岸為南界；而另外一種則為鹿野草蜥（學名暫定為T. luyeanus），分佈在立霧溪以南的東台灣。翠斑草蜥與鹿野草蜥互為姊妹種，如此接近的親緣關係及地理分佈，提供給研究高等動物雜交行為及種化現象一個很好的題材。本研究的目的，即欲利用微衛星體基因座(microsatellite)與粒線體DNA，偵測兩種草蜥在地理分佈的潛在交界地區(potential contact zone)是否有雜交現象的發生；並進而推測雜交所引發之基因滲漏（genetic introgression）的嚴重程度。 研究結果顯示翠斑草蜥與鹿野草蜥在交界地區並沒有共域的情況。從潛在的交界帶採集到的299隻個體中，利用13組微衛星體基因座及其中6組具有高分化指數的微衛星體基因座分別進行分析，其中約有3%~10.4%的個體被判斷為是雜交子代。由於僅有一隻雜交個體在粒線體DNA上帶有另一種草蜥的遺傳特徵，因此推測翠斑草蜥與鹿野草蜥的雜交現象主要是藉由雄性的基因滲透，而兩物種之間的基因滲透方向是雙向的。我們推測低比例的遷移率與天擇的壓力可能是限制翠斑草蜥與鹿野草蜥雜交現象頻繁發生的重要因素。Takydromus formosanus Boulenger 1894 includes two unpublished, cryptic species: T. viridipunctatus, distributed in northern Taiwan including Taipei, Keelung, and Yilan, with its southern boundary around the northern bank of the Liwu River; and T. luyeanus, distributed in Hualian and Taidong, with its northern boundary around the southern bank of Liwu River. The close phylogenic relationship and geographic distributions of T. viridipunctatus and T. luyeanus may provide important informations to study speciation and hybridization of higher organisms. In this study, we aim to detect the existence and degree of probable hybridization occurring in the potential contact zone between these parapatricly distributed species by using microsatellite and mitochondrial DNA markers. According to our data, sympatric distribution between T. viridipunctatus and T. luyeanus is not found in this study. However, among the 299 samples collected from the potential contact zone, about 3%~10.4% individuals were detected to be hybrids within 13-loci and 6-loci analyses. The microsatellite and/or mitochondrial DNA information of the purported hybrids show different patterns to adjacent individuals and carry genetic characters of the other species. Low proportions of hybrids carry mitochondrial DNA information of another species. It is presumed that the large proportions of equivocal individuals could be hybrids due to male introgression, and the introgression of T. viridipunctatus and T. luyeanus is bidirectional. Low dispersal rate and certain selection forces may play important roles in constraining hybridization.