Evolution, genetic basis and behavioural consequences of cuticular hydrocarbon diversification: the case of parabiotic ants

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Insect cuticles are covered with cuticular hydrocarbons (CHC). They serve two important functions: as desiccation barrier and for chemical communication. Especially in social insects, CHC profiles encode a multitude of information such as species membership, sex, reproductive caste, and colony membership. Despite their high importance, however, the evolution of CHC profiles and the underlying genetic mechanisms are little understood. Also, little is known which CHC are important for intra- and interspecific recognition.We propose to investigate a model system which is highly suited for addressing such questions. The neotropical ants Crematogaster levior and Camponotus femoratus are parabiotically associated, i.e. they share a common nest in a mutualistic way. Their CHC profiles are unusually diverse: in both taxa, multiple chemotypes exist, which have few or no compounds in common. In contrast, CHC variation in most other species is restricted to quantitative variation of the same compounds. Thus, our model system shows high chemical variability between closely related individuals, which are likely to be physiologically and ecologically similar. This unique combination opens up intriguing opportunities to investigate the evolution of cuticular hydrocarbon profiles, the causes and consequences of chemical diversification and its role for speciation. We will study the genetic basis of CHC diversity as well as the role of chemical differentiation for intra- and interspecific communication.First, we will study genetic and chemical differentiation across populations of Cr. levior in French Guiana, and elucidate population structure using genotyping by sequencing (GBS). This will allow us to investigate the relations of genetic, chemical and geographic distance to reveal the role of chemical differentiation for reproductive isolation and speciation. Second, we will study how chemical differentiation affects nestmate recognition and recognition by an associated species. Using behavioural assays with CHC fractions, we will study which CHC classes are relevant for intra- and interspecific recognition.For both Cr. levior and Ca. femoratus, we will investigate which genes are differentially expressed and/or differentially selected in different chemotypes. Our results will provide novel insights into the genetic regulation of CHC differentiation, which is still largely unknown. To verify the functionality of identified candidate loci, we will silence them via RNAi and determine the effect on CHC profiles. The biological relevance of CHC changes for nestmate and species recognition will be determined in aggression bioassays. The high CHC variation between chemotypes suggests that small changes on DNA and/or regulatory level suffice to induce large-scale changes in the CHC profile. Our project will provide a multitude of novel insights on the evolution, genetic mechanisms and behavioural consequences of cuticular hydrocarbon diversification in ants.