Data from: Transcriptional variation associated with cactus host plant adaptation in Drosophila mettleri

Although the importance of host plant chemistry in plant-insect interactions is widely accepted, the genetic basis of adaptation to host plants is not well understood. Here, we investigate transcriptional changes associated with a host plant shift in Drosophila mettleri. While D. mettleri is distributed mainly throughout the Sonoran Desert where it specializes on columnar cacti (Carnegiea gigantea and Pachycereus pringleii), a population on Santa Catalina Island has shifted to chemically divergent coastal prickly pear cactus (Opuntia littoralis). We compared gene expression of larvae from the Sonoran Desert and Santa Catalina Island when reared on saguaro (C. gigantea), coastal prickly pear, and laboratory food. Consistent with expectations based on the complexity and toxicity of cactus relative to laboratory food, within population comparisons between larvae reared on these food sources revealed transcriptional differences in detoxification and other metabolic pathways. The majority of transcriptional differences between populations on the cactus hosts were independent of the rearing environment, and included a disproportionate number of genes involved in processes relevant to host plant adaptation (e.g. detoxification, central metabolism, and chemosensory pathways). Comparisons of transcriptional reaction norms between the two populations revealed extensive shared plasticity that likely allowed colonization of coastal prickly pear on Santa Catalina Island. We also found that while plasticity may have facilitated subsequent adaptive divergence in gene expression between populations, the majority of genes that differed in expression on the novel host were not transcriptionally plastic in the presumed ancestral state.尽管宿主植物化学物质在植物-昆虫互作中的重要性已得到广泛认可，但昆虫适应宿主植物的遗传基础仍未被充分阐明。本研究以墨翅果蝇（Drosophila mettleri）为对象，探究其宿主植物转换相关的转录组变化。墨翅果蝇主要分布于索诺兰沙漠，其天然宿主为柱状仙人掌（巨人柱仙人掌Carnegiea gigantea和节柱仙人掌Pachycereus pringleii）；而圣卡塔利娜岛上的该果蝇种群已转换为取食化学组成差异显著的海岸梨果仙人掌（Opuntia littoralis）。我们分别对取食巨人柱仙人掌、海岸梨果仙人掌以及实验室人工饲料的索诺兰沙漠种群与圣卡塔利娜岛种群的幼虫进行了基因表达比较分析。相较于实验室人工饲料，仙人掌的化学组成更为复杂且具有毒性，这一特性与我们的预期相符：对同一种群内取食不同饲料的幼虫进行比较分析，发现其解毒代谢与其他代谢通路存在转录水平差异。在仙人掌宿主上饲养时，两个种群间的绝大多数转录差异不受饲养环境的影响，且其中显著富集了与宿主植物适应相关的基因（如解毒代谢、中心代谢以及化学感应通路相关基因）。对两个种群的转录反应规范进行比较后发现，二者存在广泛的共享可塑性，这或许助力了圣卡塔利娜岛种群成功定殖海岸梨果仙人掌。本研究同时发现，尽管可塑性或许推动了后续种群间基因表达的适应性分化，但在新型宿主上出现表达差异的绝大多数基因，在推测的祖先种群状态下并不具备转录可塑性。