蝴蝶的基因體顯示種間混亂的基因交換與擬態適應
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| Fig. 1 本研究定序的目標物種的分佈與其相關類群的親緣關係 |
摘要
The evolutionary importance of hybridization and introgression has long been debated. Hybrids are usually rare and unfit, but even infrequent hybridization can aid adaptation by transferring beneficial traits between species. Here we use genomic tools to investigate introgression in Heliconius, a rapidly radiating genus of neotropical butterflies widely used in studies of ecology, behaviour, mimicry and speciation. We sequenced the genome of Heliconius melpomene and compared it with other taxa to investigate chromosomal evolution in Lepidoptera and gene flow among multiple Heliconius species and races. Among 12,669 predicted genes, biologically important expansions of families of chemosensory and Hox genes are particularly noteworthy. Chromosomal organization has remained broadly conserved since the Cretaceous period, when butterflies split from the Bombyx (silkmoth) lineage. Using genomic resequencing, we show hybrid exchange of genes between three co-mimics, Heliconius melpomene, Heliconius timareta and Heliconius elevatus, especially at two genomic regions that control mimicry pattern. We infer that closely related Heliconius species exchange protective colour-pattern genes promiscuously, implying that hybridization has an important role in adaptive radiation.
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| Fig. 2 a. 毒蝶染色體與家蠶染色體同源基因的比較圖，染色體間的連線代表同源基因的來源 b. 毒蝶化學感受蛋白與大樺斑蝶、家蠶間的關係，顯示出蝴蝶獨有與毒蝶獨有的擴張 |
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| Fig. 4 這個分析顯示控制擬態斑紋的基因座B/D的在族群間的基因交換證據 |
這篇是「毒蝶是否真的交換了控制擬態斑紋的基因？」的主要基礎，作者群是很威猛的毒蝶基因體協會 (The Heliconius Genome Consortium)，透過定序數個Heliconius melpomene族群的全基因體，比較毒蝶的基因體變化與鱗翅目基因體的演化。作者群從基因體中挑出12669基因出來作各種分析，首先比較毒蝶與家蠶 (Bombyx mori)在染色體學上的差異，大部分的基因都能在家蠶上發現，但染色體位置有所差異。其次將化學感受蛋白(Chemosensory protein, CSP)的序列，加上家蠶與大樺斑蝶 (Danaus plexippus)，以系統發生學的方式分析，發現蝴蝶特有與毒蝶特有的基因擴張。毒蝶內部基因體分析則發現族群間或是共擬態者間的基因交換頻繁，特別是兩個控制擬態斑紋的基因，顯示這樣的交換可能對於毒蝶的迅速種化與斑紋的多樣化有關。
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