Acclimation in ants: Interference of communication and waterproofing through cuticular hydrocarbons in a multifunctional trait

Organismal traits may experience conflicting selection pressures if they fulfil different functions simultaneously. This can require trade-offs between functions or alternatively functional separation between elements of the trait. An important multifunctional trait in insects is the cuticular hydrocarbon (CHC) layer. CHCs cover the body of nearly all insects, protect against desiccation and serve as a communication signal. In social insects like ants, they provide cues for nestmate recognition. To maintain their waterproofing function, insects have to adjust CHC composition to current temperatures. These changes might affect information content and interfere with communication, which would be especially detrimental in social insects. Here, we studied how acclimation affects nestmate recognition in two sister species of the ant genus Lasius. Colony fragments were exposed to three climate regimes. We analysed behaviour towards same and differently acclimated conspecifics, and determined which CHCs were related to acclimatory changes, colony differences and inter-individual aggression. Differential acclimation led to higher aggression and chemical distances among former nestmates. We identified small CHC subsets, which only differed among colonies or among acclimation treatments. Moreover, few compounds sufficed to explain inter-individual aggression, suggesting that ants do not use the entire CHC profile for nestmate recognition and that colony identity is encoded in a redundant way. Across individual CHCs, their contribution to colony differences and to differences among acclimatory treatments was negatively correlated, indicating that there is some degree of functional separation. However, CHC classes could not be clearly assigned to one or another function, indicating that the role of each CHC is idiosyncratic and may differ among species. Acclimatory effects and colony differences were more independent from each other in L. platythorax than in L. niger, indicating that functional separation can differ even among sister species. Our results show that CHC functions are more intertwined than previously assumed, suggesting that insects cannot optimise all functions independently. The main constraint might be the need to maintain a certain phase behaviour of the CHC layer, which depends on CHC composition and affects functionality. The need to separate functions might depend on species-specific ecological and life-history parameters. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Organismal traits may experience conflicting selection pressures when fulfilling different functions simultaneously. In insects, the cuticular hydrocarbon (CHC) layer is an important multifunctional trait. Acclimation affects nestmate recognition and inter-individual aggression among ants by influencing CHC composition. However, there is some degree of functional separation among CHC classes, and the role of each CHC is idiosyncratic. The need to maintain a certain phase behaviour of the CHC layer might be the main constraint for insects in optimizing all CHC functions independently.