Mechanisms of host plant induced plasticity of cuticular hydrocarbon phenotypes in mustard leaf beetles

角质碳氢化合物(CHC)在昆虫的物种识别和配偶识别中起着至关重要的作用。在其他生物和非生物因素中，食物可以影响昆虫的CHC表型，这些变化可能会改变交配行为，并导致种群之间或寄主用途不同的密切相关物种之间的生殖隔离。两种寡食性芥菜叶甲Phaedon armorciae和Phaedon cochleariae共同生活在同一栖息地，但寄主用途不同。在自然条件下(寄主种类不同)，这两个物种都表现出行为隔离。然而，如果这两个物种是在同一寄主植物物种上饲养的，那么行为隔离就会被打破，两个物种会随机交配。化学分析表明，CHC表型受寄主使用的影响很大。饲养在同一寄主物种上的甲虫的CHC表型比饲养在不同寄主物种上的甲虫的CHC表型更相似，无论种群或物种同一性如何。饮食可能会对肠道微生物群产生重大影响。肠道微生物群的这些变化可以改变CHC的表型和交配行为。这项研究的目的是(A)调查寄主特定的分类交配是否适应后代的表现和免疫活性，以及(B)阐明食物诱导芥子甲虫CHC表型可塑性背后的机制和肠道微生物群的潜在作用。在第一步中，我们将把这两种甲虫饲养在不同的寄主植物上，以说明不同的寄主使用对肠道微生物群的影响。为了确定CHC表型变化的植物相关触发因素，我们将饲养甲虫：(I)在单一寄主物种上饲养甲虫，我们将以不同的方式操纵其叶圈微生物群；(Ii)在不同的人工饲料上饲养甲虫，这些饲料中添加不同的宿主特有的次生代谢物。下一步，我们将跟踪宿主转移后肠道微生物组的变化，以将肠道微生物组的时间变化与CHC表型的变化联系起来。此外，我们将使用RNA-SEQ方法分别分析不同宿主使用和肠道微生物群对甲虫基因表达的影响，特别关注CHC生物合成的卵母细胞。随后，选定的候选基因在宿主触发的CHC表型可塑性中的作用将通过RNA干扰(RNAi)来验证。我们的项目结果将提供关于CHC生物合成调控机制的新的基础知识，并突出种间相互作用和表型可塑性在昆虫通讯系统分化中的作用。

Cuticular hydrocarbons (CHCs) play an essential role in species and mate recognition in insects. Among other biotic and abiotic factors, diet could affect the CHC phenotype of an insect and these changes may modify the mating behavior and lead to reproductive isolation between populations or closely related species with divergent host use. The two oligophagous mustard leaf beetle species Phaedon armoraciae and Phaedon cochleariae co-occur in the same habitat, but differ in host use. Under natural conditions (different host species), both species show behavioral isolation. However, if both species were reared on the same host plant species, behavioral isolation breaks down and both species mate randomly. Chemical analyses show that the CHC phenotype is strongly affected by host use. CHC phenotypes of beetles reared on the same host species are more similar than CHC phenotypes of beetles reared on different host species, irrespective of population or species identity of the beetles. Diet could have a significant effect on the gut microbiome. These changes in the gut microbiome could change the CHC phenotype as well as the mating behaviour. The aims of this research project are (A) to investigate whether host-specific assortative mating is adaptive in terms of performance and immunocompetence of the offspring, and (B) to elucidate the mechanisms behind the diet-inducted plasticity of CHC phenotypes in mustard beetles and the potential role of the gut microbiome. In a first step, we will rear both beetle species on different host plant species to illustrate the impact of divergent host use on the gut microbiome. In order to identify the plant-associated trigger for the change in CHC phenotypes, we will rear beetles (i) on a single host species of which we will manipulate the phyllosphere microbiomes differently, and (ii) on different artificial diets that differ in the supplementation with host-specific secondary metabolites. In a next step, we will follow the change of the gut microbiome after a host shift to associate the temporal change of the gut microbiome with the change in the CHC phenotype. Furthermore, we will use an RNA-seq approach to analyse the impact of divergent host use and gut microbiomes, respectively, on gene expression in beetles with a special focus on oenocytes, the site of CHC biosynthesis. Subsequently, the role of selected candidate genes in host-triggered plasticity of CHC phenotypes will be validated by RNA interference (RNAi). The results of our project will provide new fundamental knowledge about the regulatory mechanisms of the CHC biosynthesis and highlight the role of interspecific interactions and phenotypic plasticity in the divergence of communication systems in insects.