Data from: Divergence of cuticular hydrocarbons in two sympatric grasshopper species and the evolution of fatty acid synthases and elongases across insects

Cuticular hydrocarbons (CHCs) play a major role in the evolution of reproductive isolation between insect species. The CHC profiles of two closely related sympatric grasshopper species, Chorthippus biguttulus and C. mollis, differ mainly in the position of the first methyl group in major methyl-branched CHCs. The position of methyl branches is determined either by a fatty acid synthase (FAS) or by elongases. Both protein families showed an expansion in insects. Interestingly, the FAS family showed several lineage-specific expansions, especially in insect orders with highly diverse methyl-branched CHC profiles. We found five putative FASs and 12 putative elongases in the reference transcriptomes for both species. A dN/dS test showed no evidence for positive selection acting on FASs and elongases in these grasshoppers. However, one candidate FAS showed species-specific transcriptional differences and may contribute to the shift of the methyl-branch position between the species. In addition, transcript levels of four elongases were expressed differentially between the sexes. Our study indicates that complex methyl-branched CHC profiles are linked to an expansion of FASs genes, but that species differences can also mediated at the transcriptional level.表皮碳氢化合物（Cuticular hydrocarbons, CHCs）在昆虫物种间生殖隔离的演化进程中发挥核心作用。两种近缘同域分布的蝗虫物种——长翅戟纹蝗（Chorthippus biguttulus）与软戟纹蝗（C. mollis）的CHC谱，其主要差异在于主要甲基支链型CHCs的首个甲基基团所处位置。甲基支链的位置由脂肪酸合酶（fatty acid synthase, FAS）或延伸酶（elongases）决定。这两类蛋白质家族在昆虫中均出现了扩张现象。值得注意的是，FAS家族存在多次支系特异性扩张，尤其在甲基支链CHC谱高度多样化的昆虫目中尤为显著。我们在两个物种的参考转录组中分别鉴定出5个推定的FAS基因与12个推定的延伸酶基因。dN/dS检测未发现证据表明这些蝗虫体内的FAS与延伸酶受到正向选择作用。然而，其中一个候选FAS基因呈现出物种特异性的转录差异，或可推动两个物种间甲基支链位置的演化转变。此外，4个延伸酶基因的转录水平在雌雄个体间存在显著差异。本研究表明，复杂的甲基支链型CHC谱与FAS基因家族的扩张存在关联，而物种间的差异也可通过转录水平的调控得以实现。