Abstract

Sociality and fungiculture independently evolved multiple times in wood-boring weevils. Interestingly, these lineages vary in ploidy levels (haplodiploidy vs. diploidy) and mating systems (inbreeding vs. outbreeding), which makes them ideal models for testing the importance of these factors for social evolution. Here I present our most recent findings on our focal species, Xyleborinus saxesenii, which demonstrate the potential of wood-boring weevils for studies on social evolution and evolution of symbiosis. This species is facultatively eusocial, i.e. given optimal conditions many females decide to delay dispersal from the mother’s nest and help to rear their siblings. In a selection experiment on either early dispersal or philopatry, we show that philopatric and cooperative behaviours are jointly selectable in females. Remarkably, this is the first successful selection for cooperative behaviour in an animal and thus unravels important trade-offs and mechanisms underlying the evolution of sociality. In the following, it will be of utmost importance to investigate the underlying genetic mechanisms that facilitate such processes. However, this would be meaningless without investigating the main driver of beetle sociality – fungiculture. Sociality apparently evolved only in weevils nutritionally associated with fungi. Fungal yields are probably higher in socially maintained nests, but to be sure I study also the mechanisms of beetle fungiculture. Several symbiotic fungi and bacteria occur in ambrosia beetle nests and I currently aim (i) to identify the role of the major microbial players, (ii) to understand how those interact with each other and most importantly (iii) to explore how the beneficial crops are maintained and defended against fungal weeds.