Changes in gene expression align with behavioural differences in reproductive choices in a social beetle.

Social animals often share their colony with individuals of different relatedness levels and life stages. In most social insects, the society structure consists of only one or a few reproducing females in the colony. When no reproductive depression is in place, a fertile female must, therefore, choose whether to stay with its natal group and limit her reproductive potential or leave to establish a new colony. The factors governing and following this reproductive decision are still largely unknown. The date stone beetle, Coccotrypes dactyliperda (Curculiondae), resides in intricate galleries carved inside date seeds. Sib mating is common in this species, and the inbreeding coefficient is high. While most females in a natal group stay and raise their offspring with their sisters, some females leave the group to start a colony of their own, regardless of the resources available within the natal group. In this study, we hypothesized that dispersing females should present physiological changes consistent with the anticipated challenges, including finding a host and egg laying, while the physiology of females that stay in the natal seed should demonstrate adaptation related to cohabiting in an existing nest. To test our hypothesis, we examined the development of ovaries in females that left the natal seed and their sisters that remained in the seed. In addition, we sequenced and analysed the transcriptome of pooled groups of females that left the natal seed and their sisters that stayed. Our physiological and transcriptomic results indicate that females that left the natal seed exhibit greater ovarian development compared to females that remained in the seed. Our transcriptomic data revealed further differences between the two groups, including genes related to nest-mate recognition and other physiological adaptations. Our study is the first to link behaviour, physiological changes and transcriptomic analyses with decision-making in relation to reproductive strategies in a social beetle.