Biophysical and functional consequences of cuticular hydrocarbon variation in ants

角质层碳氢化合物（CHCs）几乎覆盖了所有昆虫的身体。它们的组成是高度可变的：种内（如同化）变异涉及相同碳氢化合物的数量变化，而不同的物种可以拥有完全不同的碳氢化合物。CHC层可以防止干燥，抵抗病原体，并作为通信信号。虽然人们正在深入研究CHC变异对传播的作用，但对它如何影响防水和抵御病原体的能力知之甚少。这两种功能在很大程度上取决于碳氢化合物分子之间的相互作用，这些相互作用影响CHC层的相行为、熔化行为和粘度。我们仍然不知道CHC的变化是如何决定这些物理特征的，以及它们是如何影响CHC的功能的。在这里，我建议研究CHC的变化如何影响蚂蚁的物理CHC特性以及防水和抵抗真菌病原体的能力。首先，我将研究两种蚂蚁的种内变化：大陆种群和海洋种群的适应CHC变化程度（反应规范）。在适应过程中，昆虫改变其CHC曲线以增强抗旱性。面对更强的波动，大陆种群应该进化出更大的反应规范，从而比海洋种群有更好的应对波动的能力。这两个物种的殖民地将沿着欧洲的海洋-大陆梯度收集，并在不同的温度制度下进行驯化。随后，我们将研究CHC变化和驯化相关的生物物理特性、干旱存活、透水性和CHC诱导的真菌病原体生长抑制的变化。它们将在不同政权之间进行比较，也将在不同人口之间进行比较。其次，我将研究种间变化，重点研究昆虫物种间最突出的CHC差异：它们是以不饱和烃为主还是以多支烷烃为主。这种区别解释了种间CHC变异的主要部分，而几乎所有昆虫都有正构烷烃。我们将比较两种剖面类型的物种在物理特性、防水能力和真菌生长抑制方面的差异。特别是，我们将研究这些特征如何依赖于当前温度，以及它们如何随着适应CHC的变化而变化。综上所述，该项目将化学成分与CHC层的物理表型和功能联系起来。特别是CHC组成（除正构烷烃外）与物理特性之间的联系是新颖的，以前几乎没有研究过。它将揭示哪些化学和物理性状在生物选择下，从而有助于我们对CHC进化的理解。此外，我们将能够评估物种和同种种群如何应对不同的气候。这对于预测它们如何应对气候变化至关重要。

Cuticular hydrocarbons (CHCs) cover the body of nearly all insects. Their composition is highly variable: intraspecific (e.g. acclimatory) variation concerns quantitative changes of the same hydrocarbons, whereas different species can possess entirely different hydrocarbons. The CHC layer protects against desiccation, against pathogens, and serves as communication signal. While the role of CHC variation for communication is being intensively studied, considerably less is known about how it affects waterproofing and the ability to fend off pathogens. Both functions are largely determined by interactions between hydrocarbon molecules, which affect phase behaviour, melting behaviour, and viscosity of the CHC layer. We still hardly know how CHC variation determines these physical traits, and how they affect CHC functionality. Here, I propose to study how CHC variation affects physical CHC traits and the ability to waterproof and protect against fungal pathogens, in ants. Firstly, I will study intraspecific variation in two ant species: the extent of acclimatory CHC changes (the reaction norm) among continental and maritime populations. During acclimation, insects change their CHC profiles to enhance drought resistance. Being exposed to stronger fluctuations, continental populations should have evolved a larger reaction norm and thus a better ability to cope with fluctuations, than maritime ones. Colonies of both species will be collected along a maritime-continental gradient across Europe and acclimated at different temperature regimes. Subsequently, we will investigate CHC changes and acclimation-related changes in biophysical properties, drought survival, water permeability and CHC-induced growth inhibition of fungal pathogens. They will be compared across regimes, but also across populations. Secondly I will study interspecific variation, focusing on the most prominent CHC difference among insect species: whether they are dominated by unsaturated hydrocarbons or by multiply branched alkanes. This distinction explains a major part of interspecific CHC variation, whereas nearly all insects have n-alkanes. We will compare species of the two profile types concerning physical traits, waterproofing ability and the inhibition of fungal growth. In particular, we will investigate how these traits depend on the current temperature and how they change along with acclimatory CHC changes. Taken together, this project will link chemical composition to the physical phenotype and functionality of CHC layers. Especially the link between CHC composition (beyond n-alkanes) and physical traits is novel and has hardly been studied before. It will reveal which chemical and physical traits are under biological selection, and hence contribute to our understanding of CHC evolution. Moreover, we will be able to assess how species and conspecific populations can deal with different climates. This will be crucial to predict how they respond to climate change.