取食蘚苔的小翅蛾為異域種化而非寄主轉移所產生的輻射演化

文章來源：Y Imada, A Kawakita & M Kato. Allopatric distribution and diversification without niche shift in a bryophyte-feeding basal moth lineage (Lepidoptera：Micropterigidae). Proc. R. Soc. B doi:10.1098/rspb.2011.0134 Published online.

簡介
鱗翅目昆蟲的多樣性極高，最常被提及的解釋為昆蟲與寄主植物的共演化，即植物演化出可抵抗飢餓幼蟲的化學物質，而植食性鱗翅目幼蟲則演化出可以克服該化學物 質的策略，或者轉換到另一種寄主植物上。因此，有數十萬種的植物，就可能會演化出數十萬種鱗翅目昆蟲，然而從一個對較原始的蛾類-小翅蛾科所得到最新的研 究顯示演化的故事不只「生態上的種化」如此簡單。
小翅蛾從侏儸紀至今都沒有與被子植物互動過，但是他們在日本群島中仍有適度的多樣性，日本京都大學Yume Imada的研究團隊在日本群島廣泛採集小翅蛾科昆蟲，同時採集幼蟲並鑑定其寄主蘚類，並以DNA樣本重建其親緣關係，結果發現有25個不同的物種在 1500-3500萬年前之間演化出來，而這些物種的寄主皆相同-他們都取食蛇苔 (或稱蛇蘚，Conocephalum conicum)， 顯示他們佔有相同的生態棲位，且他們都生活在潮濕多苔蘚的環境中。作者認為棲位移轉造成物種分化的可能性很低，由於這些小翅蛾的飛行能力不佳，被侷限於溪 流沿岸的潮濕環境裡，因此不同地區的族群受地理上的隔離，為異域種化的結果。作者表示此研究是目前所知無涉明顯的棲位分化之最大輻射演化案例。
芬蘭學者Tommi Nyman 等人於2010年發表在BMC Evol. Biol.上的研究，也以葉蜂為材料獲得相近的結果，Nyman認為生態上的種化因為題材有趣而受到矚目，並猜測由生態因素種化而來的植食性昆蟲約佔 20-50%，但是異域種化的例子就相對受到忽視。Imada與其團隊猜測晚近利用不同寄主植物的物種並不盡然會因為移入不同的棲位而演化出不同的物種， 可能的方案是在初期的異域種化後伴隨或接著發生寄主選擇的微幅分化；此方案也可能有助於說明為何相近的昆蟲類群經常取食關係近緣的植物。

ABSTRACT
The Lepidoptera represent one of the most successful radiations of plant-feeding insects, which predominantly took place within angiosperms beginning in the Cretaceous period. Angiosperm colonization is thought to underlie the evolutionary success of the Lepidoptera because angiosperms provide an enormous range of niches for ecological speciation to take place. By contrast, the basal lepidopteran lineage, Micropterigidae, remained unassociated with angiosperms since Jurassic times but nevertheless achieved a modest diversity in the Japanese Archipelago. We explored the causes and processes of diversification of the Japanese micropterigid moths by performing molecular phylogenetic analysis and extensive ecological surveying. Phylogenetic analysis recovered a monophyletic group of approximately 25 East Asian endemic species that feed exclusively on the liverwort Conocephalum conicum, suggesting that niche shifts hardly played a role in their diversification. Consistent with the low flying ability of micropterigid moths, the distributions of the Conocephalum specialists are each localized and allopatric, indicating that speciation by geographical isolation has been the major process shaping the diversity of Japanese Micropterigidae. To our knowledge, this is the largest radiation of herbivorous insects that does not accompany any apparent niche differentiation. We suggest that the significance of non-ecological speciation during the diversification of the Lepidoptera is commonly underestimated.
Keywords: Eriocraniidae; non-glossatan moths; Japan; molecular dating

其他相關參考資料：
1. Nature News: Moths diversify without changing diet
2. Nyman, T. et al. BMC Evol. Biol. 10, 266 (2010). | Article | PubMed |