Effects of selection for early dispersal on the ambrosia beetle Xyleborinus saxesenii and its fungal symbionts

Overlapping generations is a defining characteristic of advanced social life. In cooperative breeding societies, for example, 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 number of helpers and their delayed dispersal period 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 cooperatively breeding ambrosia beetle Xyleborinus saxesenii. Two lineages of beetles were bred in the laboratory for five successive 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. The laboratory rearing resulted in an increasing proportion of successful nests in both lineages. Additionally, the control lineage exhibited a reduction in lifespan and in productivity. Furthermore, significant differences were observed in the fungal communities from the third generation onwards. The results suggest that X. saxesenii has limited potential to respond to this selection pressure, potentially due to sibmating and resulting low genetic variability. Furthermore, the correlation between nest lifespan and productivity is a crucial factor in explaining philopatry and altruism in this species.