Artificial Selection of Early Emerging Helpers in the Cooperatively Breeding Ambrosia Beetle

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 dispersing and reproducing 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 female helpers on the life history, behaviour and fungal symbionts in the ambrosia beetle Xyleborinus saxesenii. Two lineages were bred in the laboratory over the course of five generations, originating from the mixed offspring of two females caught in the wild. 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, these traits recovered to levels similar to those observed at the beginning of the experiment. Furthermore, significant differences in the fungal community were associated with our selection from the fourth generation onwards. The results suggest that X. saxesenii did not respond to our selection pressure. This may be due to the species' low genetic variability, which is the result of its sib-mating habits, or its high phenotypic plasticity with regard to social behaviour.