多重基因架構下的親緣關係，顯示毒蝶的漸進性輻射演化
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| photo: NSF |
摘要
Müllerian mimicry among Neotropical Heliconiini butterflies is an excellent example of natural selection, associated with the diversification of a large continental-scale radiation. Some of the processes driving the evolution of mimicry rings are likely to generate incongruent phylogenetic signals across the assemblage, and thus pose a challenge for systematics. We use a data set of 22 mitochondrial and nuclear markers from 92% of species in the tribe, obtained by Sanger sequencing and de novo assembly of short read data, to re-examine the phylogeny of Heliconiini with both supermatrix and multispecies coalescent approaches, characterize the patterns of conflicting signal, and compare the performance of various methodological approaches to reflect the heterogeneity across the data. Despite the large extent of reticulate signal and strong conflict between markers, nearly identical topologies are consistently recovered by most of the analyses, although the supermatrix approach failed to reflect the underlying variation in the history of individual loci. However, the supermatrix represents a useful approximation where multiple rare species represented by short sequences can be incorporated easily. The first comprehensive, time-calibrated phylogeny of this group is used to test the hypotheses of a diversification rate increase driven by the dramatic environmental changes in the Neotropics over the past 23 myr, or changes caused by diversity-dependent effects on the rate of diversification.We find that the rate of diversification has increased on the branch leading to the presently most species-rich genus Heliconius, but the change occurred gradually and cannot be unequivocally attributed to a specific environmental driver. Our study provides comprehensive comparison of philosophically distinct species tree reconstruction methods and provides insights into the diversification of an important insect radiation in the most biodiverse region of the planet.
說起毒蝶 (Heliconius)的故事，真是怎麼說也說不完，有關研究怎麼做也做不完。（文章也怎麼看都看不完.....）
早在大概二十世紀初的時候，一群研究毒蝶的科學家以當時的分子生物學技術，增幅幾個在粒腺體內的基因，重建毒蝶的演化歷史，終於得到一個長久以來疑問的證據：這些長的很像的毒蝶的親緣關係不是最近緣的，因此得知這些擬態的斑紋都是趨同演化來的。
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| Beltrán et al (2002) 以四個基因片段為基礎重建的親緣關係，包含25毒蝶屬物種與有關的外群 |
一開始就說，毒蝶的故事說也說不完，舊的議題配上新的技術是可以弄出新梗的。由於早年技術限制的問題，用的基因片段不多，種類也不多，只能看出個大概的輪廓，於是這個作者群重新檢驗毒蝶族 (Heliconiini) 的親緣關係，取樣了92%的物種以及22個基因，再次建立這個系統發生樹，並且輔以定年的資料，深入探討演化的歷史。
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| Fig. 1 本篇的主要結果，左下角為分化速率，越紅表示分化速率越快。作者同時將某些重要地理事件以紅線與雪花表示，並未與某些特定的節點產生關聯。 |
毒蝶的故事，看起來還會繼續綿延下去，科學家的奮鬥將永不止息！
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