帶著基因走：蝴蝶新斑紋的演化起源可能來自基因滲透
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標題：Evolutionary Novelty in a Butterfly Wing Pattern through Enhancer Shuffling
摘要
An important goal in evolutionary biology is to understand the genetic changes underlying novel morphological structures. We investigated the origins of a complex wing pattern found among Amazonian Heliconius butterflies. Genome sequence data from 142 individuals across 17 species identified narrow regions associated with two distinct red colour pattern elements, dennis and ray. We hypothesise that these modules in non-coding sequence represent distinct cis-regulatory loci that control expression of the transcription factor optix, which in turn controls red pattern variation across Heliconius. Phylogenetic analysis of the two elements demonstrated that they have distinct evolutionary histories and that novel adaptive morphological variation was created by shuffling these cis-regulatory modules through recombination between divergent lineages. In addition, recombination of modules into different combinations within species further contributes to diversity. Analysis of the timing of diversification in these two regions supports the hypothesis of introgression moving regulatory modules between species, rather than shared ancestral variation. The dennis phenotype introgressed into Heliconius melpomene at about the same time that ray originated in this group, while ray introgressed back into H. elevatus much more recently. We show that shuffling of existing enhancer elements both within and between species provides a mechanism for rapid diversification and generation of novel morphological combinations during adaptive radiation.
穆氏擬態間的物種是如此的相似，這樣的相似度到底是怎麼造成的一直是演化一個很大的挑戰。只考慮捕食者，好像沒辦法造成這樣的相似度；只考慮性擇，似乎無法解釋種間的趨同演化；又難道跟這些都無關，只是因為他們的祖先就是長這樣，所以後代子孫長的都一樣？
穆氏擬態的毒蝶（Heliconius）是個討論這樣的問題非常好的模型，每個區域各自有多態型，但在區域內的不同種蝴蝶都十分相像先前的研究已經告訴我們，這些看起來十分相似的蝴蝶，都是來自各自不同的支系，也就是斑紋的相似不是因為祖先的型態限制。
photo from present article photo from present article
這個研究從基因體著手，他們主要觀測的是這的擬態群的兩個紅色的區域－dennis（前翅基部部分）與ray（後翅放射狀的部分），他們假設有個順式調控基因(cis-regulatory loci)來調控一個轉錄子（transcription factor）optix，這是調控毒蝶紅色部份表現的轉錄子。結果顯示這些擬態的物種都不是最近的群，也就再次肯定了斑紋不是來自祖先的假設。而這個順式調控基因廣泛出現在這群蝴蝶內，顯示擬態的斑紋可以透過族群間的基因滲透在不同種間傳遞。他們也利用這個結果討論這個基因的滲透歷史（下圖），說明這些趨同的斑紋可能是透過雜交來傳遞，並藉由天擇來強化這個斑紋的選汰。
photo from present article
不過再怎麼說，這也還是同個屬內的東西，如果是跨科的物種的擬態群還是十分相似，但親緣關係很遠，應該不會也是透過基因滲透來傳遞的吧（如果透過Wolbachia不知有沒有可能？）
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