臺灣及鄰近地區草蜥屬的親緣關係與親緣地理學研究（有鱗目：蜥蜴科）

Phylogeny and Phylogeographic Studies of Takydromus in Taiwan and Adjacent Regions (Squamata: Lacertidae)

林思民(Si-Min Lin)

指導教授 ： 呂光洋

國立臺灣師範大學/理學院/生物學系/博士(2002年)

摘要

中文摘要
草蜥屬（Takydromus）在分類上屬於有鱗目（Squamata）、蜥蜴科（Lacertidae），主要分佈於東亞地區，喜歡棲息於草生地或森林邊緣。這個屬在本研究進行之初共有16至17種，並依其型態特徵區分為草蜥（Takydromus）與地蜥（Platyplacopus）兩個亞屬。這個屬有大約一半的種類分佈於日本、琉球與台灣，並形成當地的島嶼特有種。因此，利用分子工具，並結合地質變動的歷史，從不同的分類階層探討草蜥屬在東亞島嶼地區的演化歷史，即為本論文的主要目的（第一章）。
首先藉由定序完整的粒線體12S rRNA基因，以建立草蜥屬的親緣關係（第二章）。分子親緣關係顯示草蜥屬可粗略分為三大群，但是草蜥亞屬與地蜥亞屬並不各自形成單系群，而且部分種類的演化地位與傳統外部型態推測的結果有明顯的差異。草蜥屬在東亞島嶼地區的演化過程與島嶼之間相連接的歷史具有密切的關連，而島嶼之間因為冰河退去所造成的隔離演化效應（vicariance），可能是造成島嶼特有草蜥發生種化的主要因素。另一方面，由於草蜥種與種之間的遺傳距離上下差距極大，顯示較原始草蜥與較晚近草蜥的種化事件並非源自於同一系列的地質歷史事件。因此，依據分子生物與地質變動歷史的資料，我提出草蜥屬在東亞地區的「多次入侵」理論，用以解釋這些不同群草蜥在台灣的分佈及起源。根據分子時鐘的估算，可以讓我們大致掌握歷史上每一個分歧事件發生的時間。這個估算出來的演化速率，亦將在後續的討論之中多次被引用。
島嶼間的隔離效應雖然可以解釋大部分草蜥的種化機制，但是卻不含括所有可能的原因。台灣島由於地形崎嶇，山脈本身對陸域生物形成明顯的隔離效應。在第三章之中，我要介紹草蜥島內種化（in situ speciation）的案例。我於全島各地廣泛採集台灣草蜥（T. formosanus）的樣本，定序了兩個粒線體基因片段之後，發現東部、西部與北部的台灣草蜥在序列上擁有極大的差異，在外觀上亦具備可鑑別的特徵。其中，北部的族群與東部的族群應可提升為獨立的新種。這三個種與高海拔的雪山草蜥（T. hsuehshanensis）、高緯度的白條草蜥（T. wolteri）共同形成一個近緣的「台灣草蜥複合種群」（T. formosanus species complex），而這五個種之間的演化過程，亦將在第三章中進行詳細的討論。
在第四章，探討對象則鎖定為單一種內的演化歷史。我採集來自台灣西部14個地點的蓬萊草蜥（T. stejnegeri），進行族群遺傳與親緣地理學的探討。依據分子證據，蓬萊草蜥在種下可分為二到三個明確的系群（lineage），而其中最主要的兩個系群在台灣北部形成共域分佈的交會帶。我因此推測蓬萊草蜥極有可能在冰河時期居於不同的避難所內，因而形成明顯系群的分化；並由於冰河時期結束之後產生明顯的族群擴張，因此造成兩個系群在分佈上的重疊。利用網狀聚群分析（nested clade analysis）、中性檢測（neutrality tests）與單一位點突變頻率分析（frequency spectrum）等不同方法，結果均顯示蓬萊草蜥在最近地質變動歷史中的族群擴張現象。
由於冰河事件在地質史上的反覆出現，導致所有的陸域生物均受到這種氣候反覆變化的影響，進而發生族群數量的擴張與退縮。我將網狀聚群分析（nested clade analysis）的技術應用在台灣草蜥複合種群的四個特有種上，試圖找出物種在族群波動歷史上的共通性（第五章）。結果顯示分佈於平地的北部新種與東部新種的族群遺傳結構與蓬萊草蜥類似，並顯現出更明顯的族群歷史性波動。這三個種均呈現明確但部分重疊的兩個系群，極為可能是冰河時期結束之後發生族群擴張的結果。但是分佈於西部平地的台灣草蜥族群，相較之下呈現較為穩定的族群歷史。我推測其與共域之蓬萊草蜥間的種間競爭，可能是導致其族群在冰河結束之後無法大量擴張的因素。另一方面，依據推測，分佈於高山的雪山草蜥，應該在冰河結束之後呈現族群退縮的趨勢。但可能受限於網狀聚群分析的分析效力，亦可能受限於樣本數量的大小，這個結果在分析之中並不明顯。
在經過這些研究之後，發現台灣地區同時分佈著七種草蜥，並包含六個特有種。由於草蜥屬的共域分佈現象在其他地方相當罕見，因此這樣的種類密度，在世界上是獨一無二的。然而直至目前為止，我們對草蜥生態上或分佈上的瞭解，仍然極為有限。在第六章之中，我將對未來的相關研究題材提出展望，並對上述的研究進行總結。

關鍵字

草蜥屬 ； 親緣關係 ； 親緣地理學 ； 粒線體DNA

並列摘要

Abstract
The East Asian grass lizard genus, Takydromus Daudin in the family Lacertidae, is distributed in the Oriental and Palearctic regions. With specialized slender body shape and extraordinarily long tails, most Takydromus species inhabit in grasslands, dense scrub, or forest edge. At the beginning of my study in 1998, there were 16 or 17 species recognized in this genus, belonging to two subgenera: Takydromus and Platyplacopus. One of the most spectacular features of grass lizards in biogeography is the high percentage of endemism in the islands. Almost half of Takydromus species are endemic to the islands aligned along the Pacific coast of the East Asian continent. The formation and evolution of Takydromus in this region is an interesting issue in biogeography research (Chapter 1).
In Chapter 2, I sequenced the complete mitochondrial 12S rRNA from 14 Takydromus OTUs. Phylogenetic relationship was constructed by MP, NJ and ML methods, and the results of these three criterions are congruent. Three major groups were identified within this genus, whereas the monophyly of both subgenera was not supported. According to our deduction, the speciation process of Takydromus is closely related to the pattern of land connection among island groups influenced by glaciations. The vicariance between neighboring islands triggered the divergence between species. Furthermore, a model of multiple colonizations was proposed to explain the prominent difference of interspecific distance among different Takydromus groups. A rough estimation on the evolutionary rate helps us to deduce the age of each historical event, while this estimation would also be applied in the following sections.
Although the model of inter-island vicariance explained the distribution of most Takydromus species, an “ in situ speciation ” model was further proposed to explain the biodiversity of grass lizard in Taiwan. In Chapter 3, I collected T. formosanus from 27 locations throughout the entire island. Mitochondrial sequencing represented significant differentiation among eastern, western, and northern populations in Taiwan. With diagnostic morphological characters, two of these “evolutionarily significant units”, the northern lineage and the eastern lineage, were suggested to evaluate as new species. The combination of T. formosanus, T. hsuehshanensis, and T. wolteri formed a monophyletic group, and was defined as “Takydromus formosanus species complex”. The evolutionary relationship among the five members within this species complex was discussed in Chapter 3.
In Chapter 4, I focused on the population genetic study of Takydromus stejnegeri, another island-endemic species in Taiwan. Fourteen populations were collected, sequenced, and analyzed with nested clade analysis (NCA). Two to three major lineages were detected in T. stejnegeri, with partially overlapping distribution in northern Taiwan. Their current distribution was deduced to be a post-glacial expansion from two or three refugial regions. The recent history of “range expansion” for T. stejnegeri was supported by the evidence from NCA, neutrality tests, and frequency spectrum.
The periodical occurrence of glaciations caused the demographic fluctuation of these lizards. To figure out the pattern of such influences, I applied the analysis of NCA to the four endemic units of T. formosanus species complex in Chapter 5. The genetic pattern of the northern species (Takydromus sp. N) and the eastern species (Takydromus sp. E) were similar to that in T. stejnegeri, revealing a deep intraspecific branching with partially overlapping distribution. The demographic fluctuation in these two species was prominent, but not present in T. formosanus distributed in western Taiwan. An interspecific competition with T. stejnegeri is a probable explanation for its comparatively stable demographic history. On the other hand, the expected population decline in T. hsuehshanensis was not observed, probably owing to the analytical power of NCA or the adequate sampling for this species.
With seven species including six endemics, the island of Taiwan represents the highest biodiversity of Takydromus in the world. However, our knowledge on these secretive lizards is still limited. In Chapter 6, I will make some prospect on concerning studies in the future, and make a conclusive comment on the study of Takydromus in the past five years.

並列關鍵字

Takydromus ； phylogeny ； phylogeography ； mitochondrial DNA

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