Hydrocarbon divergence and reproductive isolation in Timema stick insects

Background: Individuals commonly prefer certain trait values over others when choosing their mates. If such preferences diverge between populations, they can generate behavioral reproductive isolation and thereby contribute to speciation. Reproductive isolation in insects often involves chemical communication, and cuticular hydrocarbons, in particular, serve as mate recognition signals in many species. We combined data on female cuticular hydrocarbons, interspecific mating propensity, and phylogenetics to evaluate the role of cuticular hydrocarbons in diversification of Timema walking-sticks. Results: Hydrocarbon profiles differed substantially among the nine analyzed species, as well as between partially reproductively-isolated T. cristinae populations adapted to different host plants. In no-choice trials, mating was more likely between species with similar than divergent hydrocarbon profiles, even after correcting for genetic divergences. The macroevolution of hydrocarbon profiles, along a Timema speciesphylogeny, fits best with a punctuated model of phenotypic change concentrated around speciation events, consistent with change driven by selection during the evolution of reproductive isolation. Conclusion: Altogether, our data indicate that cuticular hydrocarbon profiles vary among Timema species and populations, and that most evolutionary change in hydrocarbon profiles occurs in association with speciation events. Similarities in hydrocarbon profiles between species are correlated with interspecific mating propensities, suggesting a role for cuticular hydrocarbon profiles in mate choice and speciation in the genus Timema.

背景：个体在择偶过程中通常更倾向于选择具有特定性状值的配偶。若不同种群间的此类择偶偏好存在分化，则可产生行为生殖隔离，进而推动物种形成。昆虫的生殖隔离多依赖化学通讯，其中表皮碳氢化合物（cuticular hydrocarbons）在众多物种中均可作为配偶识别信号。本研究整合雌性个体表皮碳氢化合物数据、种间交配倾向数据与系统发育学数据，旨在评估表皮碳氢化合物在Timema属竹节虫物种多样化进程中的作用。
结果：在所分析的9个物种之间，以及适应不同寄主植物、已部分产生生殖隔离的T. cristinae种群之间，碳氢化合物谱型均存在显著差异。在无选择交配试验中，即便校正了遗传分化的影响，碳氢化合物谱型相似的物种间仍更易发生交配。基于Timema属物种系统发育树的碳氢化合物谱型宏观进化分析结果显示，其最符合以物种形成事件为核心的表型变化间断模型，这与生殖隔离进化过程中选择作用驱动的表型变化模式相一致。
结论：综合来看，本研究数据表明，Timema属物种及种群间的表皮碳氢化合物谱型存在差异，且碳氢化合物谱型的绝大多数进化变化均与物种形成事件相伴发生。物种间碳氢化合物谱型的相似性与种间交配倾向呈显著相关，这提示表皮碳氢化合物谱型在该属的配偶选择与物种形成过程中发挥了重要作用。