Behavioral dynamics between caring males and females in a beetle with facultative biparental care

In families in which both parents care for multiple offspring, the amount of care a parent provides can be simultaneously influenced by multiple social interactions (i.e., parent-parent and parent-offspring). In this study, we first tested for sex differences in the parents' contribution to care and then used path analysis to address the simultaneous impact of parent-parent and parent-offspring interactions on male and female care in the burying beetle, Nicrophorus vespilloides. In this species, both parents provision their offspring predigested carrion from a vertebrate carcass, and the larvae beg for food from their parents. We found that females were more involved in direct care for the larvae and spent more time than did males provisioning the larvae with food. By using path analysis, we found a negative relationship between male and female provisioning, suggesting that parents adjust their behavior to that of their mate. Furthermore, we found that both social interactions (i.e., larval begging) and nonsocial factors (i.e., brood size) significantly influenced male provisioning, but had no significant effect on female provisioning. We suggest that the difference in the relative contribution of the two sexes to the care of the offspring explains why only males seemed to adjust their care to variation in social and nonsocial factors. For example, females may be less able to adjust their care to variation in larval begging and brood size because they were already working near their maximum capacity.