臺灣地區煙草粉蝨亞澳地理群親緣地理學研究

Abstract

煙草粉蝨 (Bemisia tabaci) 種內具有高度遺傳變異，為重大經濟害蟲。近年來分子標誌的應用，已被區分為至少26型生物小種或12型遺傳群。過去研究顯示，中國 (China)、澳洲 (Australia) 及亞洲I (Asia I) 等3型遺傳群屬於亞澳地理群，亞洲II (Asia II) 遺傳群屬於亞洲地理群，兩地理群重疊分布於亞洲，其中亞洲地理群在親緣地理學已有初步探討。本研究選用粒線體CO1及微衛星基因座探討煙草粉蝨亞澳地理群之親緣地理學。利用粒線體CO1以貝氏法重建亞澳地理群之親緣關係樹，樹型顯示亞澳地理群可區分為中國、澳洲、亞洲及遠東等四大支系，前兩支系即分別為China與Australia遺傳群，後兩支系同屬於Asia I遺傳群。最小跨度網狀圖可區分出4型單倍群並符合前述之四大支系，單倍群間具有高序列分化程度 (7∼11%)，推測遺傳群間或遺傳群內存在隱蔽種。臺灣地區僅有China及Asia I遺傳群分布，China遺傳群僅分布於金門及馬祖，Asia I遺傳群內遠東支系及亞洲支系各自分布於臺灣島內北部及南部。此外，島內兩支系間呈現高遺傳差異與低基因交流程度，並根據臺灣地質史與昆蟲粒線體CO1之進化速率，推測臺灣亞澳地理群具有不同拓殖來源且進來時間亦不相同。進一步利用微衛星基因座探討臺灣亞澳地理群之族群結構，貝氏法分群將臺灣亞澳地理群區分為4個clusters，clusters 1及2分別與中國支系及亞洲支系相符合，clusters 3及4同屬遠東支系。遺傳分化指數與歸群分析顯示，相距20公里內之族群基因交流順暢，幾乎沒有分化。臺灣島內兩支系如同粒線體CO1之分析結果，彼此呈現高度分化，推測遺傳群內之遺傳結構已產生分歧。clusters 3及4共域分布在臺灣北部及東部，彼此呈現高度分化但仍有少量基因交流，推測兩亞群正在逐漸分歧，種內生物互動及地形阻隔為可能之成因。根據歸群分析推測族群之擴散歷史，cluster 1之馬祖族群呈現南往北之擴散方向，推測由夏季西南季風造成，臺灣島內之族群亦存在某些擴散路徑，可能與島內複雜的地形結構與種間生物互動有關。比較亞澳地理群及亞洲地理群之親緣地理結構，亞洲地理群具有複雜的單倍群結構，推測為較早拓植到臺灣之地理群。地形、氣候、生物互動及地質歷史等因子影響臺灣地區煙草粉蝨亞澳群之分布、擴散歷史及基因交流。

Bemisia tabaci (Hemiptera: Aleyrodidae) is an important pest and is known to have a high degree of intraspecific genetic diversity. More than 26 biotypes or 12 genetic groups have been designated in Bemisia tabaci. Previous studies showed that the China, Australia, and Asia I genetic groups belong to the Asia-Australia geographic group and the Asia genetic group belongs to Asia II geographic group. These two geographic groups have overlapping distributions in Asia. However, preliminary analyses have only been conducted on the Asia group. In this study, mitochondrial cytochrome oxidase I (mtCO1) and microsatellite loci were used to analyze the phylogeography of the Asia-Australia geographic group. A phylogenetic tree of Bayesian inference using CO1 data indicated that the Asia-Australia geographic group can be divided into four major clades: China, Australia, Far-East Asia and Asia clades. The first two clades respectively belong to the China and Australia genetic groups. The other two belong to Asia I genetic group. The identification of four clades is consistent with the four haplogroups distinguished through a minimum spanning network analysis of CO1 data. Sequence divergences between haplogroups reach 7∼11% and provide evidence for cryptic species among and within genetic groups. Collections in Taiwan found the China, Far-East Asia and Asia clades. Samples from the islands of Matsu and Kinmen, located off the southeastern Chinese coast, belong to the China clade. Other samples from the main island of Taiwan belong to the Far-East Asia and Asia clades. On the island of Taiwan, there is high genetic differentiation and little gene flow between the Far-East Asia and Asia clades. Therefore, the hypothesis of multiple origins with different colonization times is proposed, and this was also supported by the geological histories in the island of Taiwan and the evolutionary rate of mtCO1 in insect. Furthermore, the microsatellite loci were used to analyze the population structure of the Asia-Australia geographic group in Taiwan. The Bayesian cluster method defined the Asia-Australia geographic group into four clusters (clusters 1~4). Clusters 1 and 2 respectively match to the China and Asia clades. Clusters 3 and 4 belong to the Far-East Asia clade. FST values and an assignment test revealed high gene flow and almost no genetic differentiation in a small range of < 20 km. When including the entire Taiwanese region, the Far-East Asia and Asia clades have high genetic differentiation as shown by the results of CO1 analysis which reveal that the genetic structure has diverged within the genetic group. The distributions of clusters 3 and 4 overlap in northeastern Taiwan, but FST values and the assignment test indicated high genetic differentiation with little gene flow. This result suggests that clusters 3 and 4 are diverging on Taiwan and biological interaction between geographic groups and topographical isolation may be reasons for this. According to the assignment test, the dispersal history in cluster 1 of the Matsu population reveals a south to north trajectory which reflects the direction of southwest monsoons during the summer. Certain dispersal histories were also found on the main island of Taiwan which relate to the complex topography and interspecific biological interactions. Compared with the phylogeography between the Asia and the Asia-Australia geographic groups, the previous study showed that the former has complicated haplogroups and reveals earlier colonization in Taiwan. Topography, climate, biological interactions, and geological histories may have played important roles in the distribution, gene flow, and dispersal histories of this species in Taiwan.