The cuticular hydrocarbon variation of \(Apis\) \(mellifera\): An interplay between the environment and genetics

The western honey bee (Apis mellifera) possesses a wide distribution range across which it faces diverse climatic selective pressures. In consequence, A. mellifera has evolved into several subspecies, each of which exhibits adaptations specific to the environment within their native distribution ranges. The cuticular hydrocarbons (CHCs), which prevent water loss and mediate chemical communication, represent an interesting example of such local adaptive traits. CHCs’ biological functioning depends on their composition because the different hydrocarbons present different waterproofing capabilities. CHC composition is considered to be influenced by the environmental temperature and humidity and can be determinant for the desiccation resistance of insects. Surprisingly, the variation of CHC composition between A. mellifera subspecies has been widely neglected, despite their potential role as an adaptation to local climate. Furthermore, up to date there is no analysis on the variation of the CHC profiles of honey bees in response to diverse environmental conditions. This thesis analyzes the CHC composition and expression of CHC biosynthesis-related genes of nurse and forager bees of different subspecies, to better understand the variation of the CHC profile of honey bees in light of its role as a climatic adaptation. A series of common garden experiments were performed to disentangle the effect of the environment and genetics on the expression of the CHC profiles in the bees. The results suggest that the evolution of subspecies specific CHC profiles in A. mellifera has been largely influenced by genetic drift and/or phylogenetic constraint. These results also provide evidence of how the variation in the expression of specific CHC biosynthesis-related genes contributes to the CHC composition shift exhibited by A. mellifera workers in their nursing-to-foraging task transition. Moreover, the results evidence the adaptive plasticity of the CHC of honey bees in response to distinct environmental conditions. This work showcases the complexity of the regulation of CHC profiles and lays the ground for future research to further investigate on the genetic basis of CHC biosynthesis, the factors influencing CHC profile variation, and the impact of such variation on the biological functioning of CHCs.