台灣產多囊海鞘屬之分類及分子親緣關係

Abstract

多囊海鞘(genus Polycarpa)為個體型海鞘，大多生長於熱帶及亞熱帶的淺水域珊瑚礁或岩石上，是珊瑚礁生物群聚的重要成員。牠們的革質外鞘可以提供其他動物附生，例如：雙殼貝、多毛蟲、以及其他種海鞘等都是常見附生動物。多囊海鞘屬，全世界已知紀錄約有四十餘種，但過去在台灣的研究中只有一種之紀錄。本研究目標是了解台灣產多囊海鞘的物種多樣性及其分子親緣關係。於2005至2006年之間，在台灣沿岸海域一共採集了102隻個體經比對形態特徵，鑑定出五種多囊海鞘，其中四種為新紀錄種。在親緣關係方面，本研究選擇兩段去氧核糖核酸，粒線體細胞色素C氧化酶(COI)及核糖體轉錄區間(ITS)，做為分子標誌經由聚合酶連鎖反應(polymerase chain reaction)增幅，並經DNA定序之後，分別以鄰聚法(Neighbor-joining)、最大儉約法(Maximum-parsimony)、最大似然率(Maximum-likelihood)、及貝氏法(Bayesian method)來建構親緣關係樹，所得到的樹形大致相似，也符合形態的分群。結果也顯示，不同種多囊海鞘中的孵育型生殖模式，可能是各自獨立演化的結果，同時，在皺裂多囊海鞘中(Polycarpa rima)可能有隱蔽種(cryptic species)的存在。

The species of Polycarpa (Stolidobranchia: Styelidae) are solitary ascidians that generally occur on the surface of coral reefs or rocks in tropical and subtropical shallow waters. They are important members in marine sessile communities because their leathery tunic provides habitats for other organisms, such as bivalves, polychaetes, echinoderms and other ascidians. There are about 40 species of Polycarpa worldwide, but only one species is previously recorded in Taiwan. The objectives of this study are to explore Polycarpa species diversity in Taiwan and to infer their molecular phylogeny. In total, 102 individuals of 5 Polycarpa species were collected from northern and southern Taiwan in 2005 and 2006. Among them, 4 Polycarpa species are newly recorded in Taiwan. Partial mitochondrial cytochrome C oxidase subunit I (COI) and the nuclear ribosomal internal transcribed spacer (ITS) DNA sequences were amplified and sequenced. These sequences were applied to phylogenetic reconstruction using neighbor joining, maximum parsimony, maximum likelihood, and Bayesian methods. The topologies of phylogenetic trees reconstructed by four methods are similar. Based on the phylogeny of Polycarpa, there are two major findings: (1) brooding mode of reproduction in the Polycarpa species have evolved independently; (2) there may be a cryptic species within the Polycarpa rima complex.