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Speciation history of land snails Aegista subchinensis (Möllendorff, 1884) and its related species
divergence time estimation
southern Ryukyu Islands
|Abstract:||物種是演化生物學探討的基本單位，種化研究應基於正確的物種界定。整合多種獨立證據有助於系統分類學和種化過程的推論。琉球群島位於東亞的亞洲大陸邊緣，此區的親緣關係或親緣地理研究，大多侷限於擴散能力相對高的脊椎動物和節肢動物，而侷限於陸地且擴散能力低的生物的種化歷史尚未被研究。本論文針對分別分布於臺灣東、西部、石垣島和宮古島的四種特有大臍蝸牛，探討其種化歷史。根據分子與形態證據，分布於臺灣東部的臺灣大臍蝸牛族群為隱蔽種，描述命名新種為彩虹大臍蝸牛（第二章）。由於軟體動物可用的核基因標誌有限，因此以同屬物種的轉錄體開發新的核基因標誌（第三章）。為獲得合理可用於大臍蝸牛的分子時鐘，新定序臺灣盾蝸牛、彩虹大臍蝸牛和臺灣長蝸牛的粒線體序列，建構粒線體親緣關係樹推算柄眼目和大臍蝸牛的分化時間（第四章）。根據以上結果，進一步推測物種演化樹、族群波動歷史和歷史遺傳交流（第五章）。根據兩個粒線體基因和十個核基因重建的物種樹顯示，臺灣大臍蝸牛分化於2.05百萬年前，分布於石垣島的大臍蝸牛分化自1.55百萬年前，彩虹大臍蝸牛和分布於宮古島的大臍蝸牛則種化於1.40百萬年前。彩虹大臍蝸牛和宮古島大臍蝸牛，是由地理割裂造成的種化事件並伴隨單向遺傳交流。以統計法檢測高變異分子標誌，未顯示有族群擴張的現象，而extended Bayesian skyline plot成功重建族群波動歷史。|
Species is the fundamental unit for evolutionary biology. The big question of how species evolved should be based on the correct assignment of species. Integrating multiple independent evidences improve the inferences of systematics and speciation scenario. The Ryukyu Islands is an island chain located on the margin of Asia Continent in East Asia. Many phylogenetic or phylogeographic research conducted in this region were limited to vertebrates and arthropods with relatively high dispersal ability. The speciation history of terrestrial restricted animals with low dispersal ability has not yet been explored. In this dissertation, I focused on the speciation history of land snail Aegista spp. distributes in Taiwan, Ishigaki Island and Miyako Island. A cryptic species was identified from A. subchinensis in eastern Taiwan and described as a new species named A. diversifamilia based on molecular and morphological evidences (Chapter 2). Novel nuclear markers were developed from transcriptome since limited nuclear marker available for Mollusca (Chapter 3). In order to calculate a reasonable molecular clock that could be applied in Aegista spp., divergence time of Aegista was estimated based on calibrated mitogenomic phylogeny with three additional newly sequenced mitogenome, A. mackensii, A. diversifamilia and Dolicheulota formosensis (Chapter 4). Based on these results, species tree, demographic history and historical gene flow were estimated using multiple loci dataset (Chapter 5). The species tree inferred from the combination of two mitochondrial and ten nuclear DNA suggested A. subchinensis was diverged about 2.05 Mya, A. vermis separated from the common ancestor of A. diversifamilia and A. oculus at 1.55 Mya, and the latter ancestor speciated subsequently around 1.40 Mya. Vicariance speciation with asymmetric gene flow from A. diversifamilia and A. oculus was inferred based on IMa2 analysis. Statistical tests of highly polymorphic genes suggested no signature of population expansion for each species, while population fluctuation was inferred using extended Bayesian skyline plot.
|Appears in Collections:||學位論文|
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