以全球紅蛺蝶探討廣域分佈類群與其侷限分佈姊妹群之種化形成

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文獻來源: Wahlberg N. and D. Rubinoff. 2011. Vagility across Vanessa (Lepidoptera: Nymphalidae): mobility in butterfly species does not inhibit the formation and persistence of isolated sister taxa. Systematic Entomology 36(2): 362–370. [Abstract]

簡介

異域種化假設了族群間受地理隔離而無法進行基因交流，最終形成兩個獨立的分類群，因此對於廣域且活動能力強的物種來說此機制似乎無法形成隔離且侷限分佈的姊妹種。蛺蝶科紅蛺蝶屬(Vanessa)包含了許多世界性廣域分佈物種，卻也擁有不少局限分佈種，因次此屬成為測試此假說理想的材料之一。此研究藉由涵蓋全球紅蛺蝶屬與其姊妹群的取樣，使用粒腺體COI與8段核基因序列，進行親緣關係的重建與分子鐘枝系分歧的時間推估，所獲得的結果為: 1. 各基因所重建的親緣關係樹見少有衝突，且樹型符合過去形態證據所劃分的烏個紅蛺蝶種群; 2. 外群Antanartia成為駢系群，其中改屬兩物種在此研究中與Vanessa形成單系群，故以此將其轉屬，現用組合名為V. hippomene以及V. dimorphica，現今紅蛺蝶共計22種; 3. 由生物地理分析的結果呈現多數的侷限分佈種，其姊妹種為廣域分布種，因而顯示擴散分布與異域種化的存在。然而就分子定年的結果顯示這些分枝分化時間都相當久(大於500萬年)，此結果支持了長時間的隔離分化。然而作者認為紅蛺蝶屬的高活動力與異域隔離在此研究中，並無法完全解釋此屬在系統發生上的成因。

Abstract

Allopatric speciation is thought to occur in the absence of gene flow, thereby suggesting that widespread vagile species might be less likely to generate restricted sister taxa because of a lack of isolation. The butterfly genus Vanessa provides an ideal test of this concept, as it contains some of the most cosmopolitan and vagile species of butterflies on the planet, as well as some highly restricted taxa. Given the age of these groups, this arrangement offers a special opportunity to examine the relationship between vagility and phylogeny in generating novel taxa; specifically, does the vagility of some lineages impede allopatric speciation, leaving restricted clades more speciose? A phylogenetic hypothesis is proposed for all species belonging to the butterfly genus Vanessa based on DNA sequences from one mitochondrial and eight nuclear gene regions. The resulting topology shows very little conflict among gene regions, with five well-supported clades corresponding to morphologically consistent species groups. The data very strongly indicate a polyphyletic genus Antanartia, and thus to preserve monophyly two species previously assigned to Antanartia are transferred to Vanessa, Vanessa hippomene comb.n. and Vanessa dimorphica comb. n., resulting in a total of 22 species placed in Vanessa. A biogeographical analysis shows that in many cases the most geographically restricted species are sister to geographically widespread species, suggesting dispersal and allopatric speciation. Surprisingly, in almost all cases the divergences between widespread and restricted species are quite old (>5 Ma), suggesting long-term isolation and stability of both vagile and sedentary species, despite the high (even intercontinental) vagility of many extant species and, by extension, ancestral species. The biogeography of Vanessa suggests that species vagility and allopatry do not fully explain the forces governing cladogenesis in this remarkable genus.