棲地零碎化對諸羅樹蛙族群遺傳結構影響之探討

Abstract

摘 要 諸羅樹蛙（Rhacophorus arvalis Lue, Lai, and Chen, 1995），為台灣特有兩棲類，目前僅在台灣南部的雲林北港溪、嘉義朴子溪及台南(麻豆)呈不連續分布，主要棲息環境為竹林、果園、稻田，棲息地易受人為的干擾，由於本身移動能力不佳，加上雄蛙對棲地有相當程度忠誠度（site fidelity）行為，是適合探討受棲地零碎衝擊的物種。現今野外諸羅樹蛙分佈地點，依照水系流域，可分成北港溪北岸、北港溪南岸、朴子溪與曾文溪(麻豆)四個不同群族，利用120隻個體增幅粒線體COX1、cyto b與D-loop部分序列，根據單基因型(haplotype)、核酸歧異度、族群分化、交流指數、AMOVA(analysis of molecular variance)、最小關聯網狀樹狀圖(minimum spanning network)與NCA( Nested clade analysis)方法，進行族群遺傳結構探討，結果顯示諸羅樹蛙最大種內變異程度僅0.004，為國內目前已發表兩棲類中最低者，其中麻豆族群內的遺傳變異為0。另外各地族群皆從很小的有效繁殖族群而來，推測可能和歷史棲地不可測(Stochastic)的環境壓力與人為干擾有關。北港溪南、北流域族群呈現小族群快速成長，而朴子溪與麻豆族群則是受長期瓶頸效應的小族群。從地理親緣關係來看，朴子溪流域的族群，過去可能從北港溪周遭擴散遷移而來。“過去零碎”(past fragmentation) —溪流間陸域的的隔離，導致四條流域諸羅樹蛙族群缺乏基因交流，在瓶頸效應下喪失基因多樣性，存在顯著的族群結構，成為四個不同的族群。目前麻豆族群建議為短期優先保育的地區，北港溪周遭流域族群為長期保育的熱點(hotspot)。Abstract Farmland green tree frog, Rhacophorus arvalis is an endemic species of Taiwan. Its main habitats include rice fields, bamboo plantations, and orchards. These environments are frequently disturbed through various types of human activities. Currently it is found only in limited farmlands in Yunlin, Chiayi, and Tainan counties. Apparently this species is greatly threatened by habitat fragmentations and other human activities. Farmland green tree frogs have limited dispersal capabilities due to low mobility and site fidelity. It is one of the best candidate animals to study the impacts of habitat fragmentations on wildlife. Based on their current distribution, farmland green tree frogs can be separate into four populations: north bank of Peikang stream、south bank of Peikang stream、Potz stream and Madou. A total of 120 individuals were used to analyze with partial mitochondrial COX1, cyto b and D-loop gene fragments. Haplotypes, nucleotide diversity, FST, Nm, AMOVA (analysis of molecular variance), minimum spanning network and NCA (Nested clade analysis) methods were applied. The Farmland green tree frog’s maximum intra-specific genetic variance is 0.004, which is the lowest among amphibian being investigated in Taiwan. Even the genetic variance of Madou population is 0. Molecular data showed that four populations all derived from small effective breeding populations. We suspected that the historical stochastic factors and human disturbance might play important roles in this aspect. The north and south bank of Peikang stream populations both were rapid growing. Nevertheless, Potz and Madou population have experienced a period of bottleneck. The phylogeographic evidences indicate that Potz population might come from Peikang population. Data also revealed a consistent phylogeographic pattern, and indicated the results of “past fragmentation”. This leads to low gene flow among populations and bottleneck effect. Genetic variations were lost greatly among population and formed four significantly different populations. We suggest madou population given the higher priority for species conservation in short term. Population of Peikang stream is the genetic hotspot for conservation.