利用遺傳多樣性探討瘤顎家蟻屬之分子親緣關係及推測入侵紅火蟻之發生源

Abstract

為研究瘤顎家蟻屬 (Strumigenys) 之遺傳多樣性及親緣關係，從臺灣及鄰近島嶼間採集樣本，並利用核糖體 DNA (rDNA) 之第二轉錄間區 (internal transcribed spacer 2，ITS2) 及粒線體DNA (mtDNA) 之 COI、COII 序列，作為親緣關係之分析。瘤顎家蟻所增幅出的 ITS2 序列，依種類的不同，其長度呈現從 659 bp 至 943 bp 不等的變化，原因為序列中有重覆插入及消失的小片段，而這些小片段就如同微衛星 DNA (microsatellite DNA) 片段般，在 DNA 序列上重覆出現，使得 ITS2 的序列長度呈現變化。 mtDNA 的 COI 及 COII 片段長度則較一致，其平均長度分別為 782 bp 及 576 bp。在序列 CG含量的百分比上， ITS2、COI、COII 分別為 60.8%、28.9% 及 23.9%。雖然 ITS 序列長度多變，但 ITS2 的二級結構，在不同的種類間，仍可排列出相當一致的十分枝狀結構。利用最大簡約法 (Maximum parsimony，MP) 及最大概似法 (Maximum likelihood，ML) 分析11種已知種類及3種未命名種之瘤顎蟻，結果發現在馬祖群島之北竿島及西莒島所採集到的兩個未命名種，分別與蓬萊瘤顎蟻 (S. formosensis) 及日本瘤顎蟻 (S. solifontis) 關係相近。然而，ITS2 的序列資料並無法明確的分辨日本瘤顎蟻、屈尺瘤顎蟻 (S. chuchihensis)、劉氏瘤顎蟻 (S. lewisi) 及採集自馬祖之種類 (Matsu SJ) 間的關係。類似的情形也出現在 mtDNA 的 COI 及 COII 序列上。雖然 ITS2、COI 及 COII 序列在分析其親緣關係上的不一致性如此高，但是這些序列資料，仍可作為分析瘤顎家蟻在臺灣及附近島嶼間的種間親緣關係。從 12 個種類及 9 個未命種類的 67 個族群所得的 mtDNA COI 及 COII 資料，可發現在種的階層有多系 (polyphyly) 及並系 (paraphyly) 的現象發生。這樣的情形可能是由於不完整的親系分配 (lineage sorting) 造成的結果。根據 ITS2 及 mtDNA COI 及 COII 的資料，可推測瘤顎家蟻熱帶分系的種類 (包括蓬萊瘤顎蟻、蘭嶼瘤顎蟻 (S. orchidensis)、西表瘤顎蟻 (S. stenorhina) 及馬祖的未命名種 (Matsu CB) 的遷徙路徑。此外，對蓬萊瘤顎蟻在臺灣島內的擴散方向也可以推論為從北到東，再到南部的遷徙。另細毛瘤顎蟻、日本瘤顎蟻、劉氏瘤顎蟻及未命名的 Matsu SJ 的族群，則可能是以「日本－琉球－臺灣」的方向及途徑向外擴散。利用上述相同的方法，對自2003年10月成功登陸台灣之入侵紅火蟻 (Solenopsis invicta)，做可能入侵源之推測，以 66 個分別採集自桃園、台北及嘉義地區族群的樣本 (包括 2 個零星發生於宜蘭及苗栗的族群)，16 個澳洲火蟻防治中心所提供的族群，及 15 個採自美國南卡羅萊納州、路易西安納州、密西西比州及德州的樣本，以 MP 及 ML針對其 mtDNA COI 及 COII 序列分析所得之結果皆呈現出，嘉義與澳洲及大部份美國的入侵紅火蟻族群關係相近而成為一分支，桃園-台北的族群則與少部份美國的族群另成兩分支。此分支的狀況雖無法明確的描述出台灣地區入侵紅火蟻擴散的確實路徑，但可確認美國為其主要的入侵源，且可能是單源單次入侵，或是從相近的來源多次入侵。而零星發生在苗栗及宜蘭的族群，則可能是經由人為的方式由桃園-台北地區擴散出去的。

Intraspecific divergence and phylogenetic relationships of Strumigenys between different localities in Eastern Asia were respectively inferred from sequences of the internal transcribed spacer 2 (ITS2) of rDNA and cytochrome oxidase subunit I, II (COI, COII) of mtDNA. The ITS2 sequences of Strumigenys in different species vary in length from 659 to 943 bp, due to large repeated insert-deletion fragments. The length of amplified mtDNA COI and COII sequences are ca. of 782 and 576 bp. The average GC content of ITS2, COI, and COII are 60.8%, 28.9%, and 23.9%, respectively. Secondary structures from ITS2 sequences are similar and present several conserved structure motifs. Eleven species and three unidentified species of Strumigenys were analyzed using both the maximum parsimony (MP) and maximum likelihood (ML) methods by ITS2 sequences. Results revealed that two of the unidentified species from Matsu Island are closely related to S. formosensis and S. solifontis, respectively while the third unidentified species from Orchid Island seems to be closely related to S. lacunosa. However, ITS2 sequences cannot resolve the relationship of S. solifontis, S. chuchihensis, S. lewisi, and Matsu SJ. The situation was the same as mtDNA COI and COII sequences. Although the diversity in ITS2, COI, and COII sequence are high, these data can still be a potential marker for primary analysis of the molecular phylogeny of Strumigenys at the species level on islands around Taiwan. Sixty-seven populations belong to 12 species and 9 unidentified species were used in mtDNA COI and COII sequence analyses. The topologies obtained reveal similar condition with ITS2. The diversity of these two sequences is still too high to clear the relationships among species. These phenomena pointed out the species-level polyphyly or paraphyly patterns and these patterns may be due to the incomplete lineage sorting. The migrate route of four tropical group species (S. formosensis, S. orchidensis, S. stenorhina, and an unidentified species from Beigan Island (Matsu CB)), can be slightly clarified. The possibility of dispersal direction of S. formosensis can also be extrapolated from north to east and south. The S. hispida, S. solifontis, S. lewisi, and unidentified species Matsu SJ, have the prospect of Japan-Ryukyu-Taiwan pathway to disperse outward. In order to clarity the dispersal route and/or invasive origin of the red imported fire ant (Solenopsis invicta, RIFA), which was first reported from Taiwan in October 2003, the method of mtDNA COI and COII sequences analysis were also applied to RIFA. In total 66 populations were collected in Taiwan, with 35 populations from Taoyuan County, 16 populations from Chiayi County, 13 populations from Taipei County, and two scatter distributed populations in other counties. Sixteen populations from Australia provided by the Fire Ant Control Centre, and 15 populations from USA, including South Carolina, Louisiana, Mississippi, and Texas, were also used in this study. The analysis of their mtDNA COI and COII sequences by MP and ML both present same topologies. RIFA populations of Chiayi, Australia, and most United States were clustered together. Taoyuan-Taipei populations clustered with the rest populations of United States. Although this topologies can not clarify the actual invasion source and the detail routes of dispersal of RIFA, however, the most likely scenario is United States, and may be introduced singly from one place, or multiply from the same places. The occasionally invaded spots of Miaoli and Yilan would be dispersed by human activities from Taoyuan-Taipei areas.