Overlapping generations is a defining characteristic of advanced social life. In cooperative breeding societies, temporary groups of mature offspring are formed that assist in the rearing of additional brood before the offspring disperse and reproduce independently. It is hypothesized that the delayed dispersal period of helpers will determine the number of siblings that can be reared, thus resulting in an indirect fitness gain. The objective of this study, was to investigate the effect of artificial selection for early dispersal of mature offspring on the life history, behaviour and fungal symbionts in the ambrosia beetle Xyleborinus saxesenii. Two lineages were bred in the laboratory for five generations. In one group, dispersing females were selected at random to initiate the next generation, while in the other group, only early dispersers were selected. A number of life-history traits exhibited a pronounced response in the initial generation, subsequently recuperating to levels approximating those observed at the outset of the experiment. Furthermore, significant differences were observed in the fungal communities from the fourth generation onwards. The results suggest that X. saxesenii has limited potential to respond to this selection pressure, potentially due to low genetic variability.

Animal societies use nestmate recognition to protect against social cheaters and parasites. In most social insect societies individuals recognize and exclude any non-nestmates and the roles of cuticular hydrocarbons as recognition cues are well documented. Some ambrosia beetles live in cooperatively breeding societies with farmed fungus cultures that are challenging to establish, but of very high value once established. Hence, social cheaters that sneak into a nest without paying the costs of nest foundation may be selected. Therefore, nestmate recognition is also expected to exist in ambrosia beetles, but so far nobody has investigated this behavior and its underlying mechanisms. Here we studied the ability for nestmate recognition in the cooperatively breeding ambrosia beetle Xyleborinus saxesenii, combining behavioural observations and cuticular hydrocarbon analyses. Laboratory nests of X. saxesenii were exposed to foreign adult females from the same population, another population and another species. Survival as well as behaviours of the foreign female were observed. Behaviours of the receiving individuals were also observed. We expected that increasing genetic distance would cause increasing distance in chemical profiles and increasing levels of behavioural exclusion and possibly mortality. Chemical profiles differed between populations and appeared as variable as in other highly social insects. However, we found only very little evidence for behavioural exclusion of foreign individuals. Interpopulation donors left nests at a higher rate than control donors, but neither their behaviours nor the behaviours of receiver individuals within the nest showed any response to the foreign individual in either of the treatments. These results suggest that cuticular hydrocarbon profiles might be used for communication and nestmate recognition, but that behavioural exclusion of non-nestmates is either absent in X. saxesenii or agonistic encounters are so rare or subtle that they could not be detected by our method. Additional studies are needed to investigate this further.