The presence of conspecific intruders alters the magnitude of sex differences in care in a burying beetle

Biparental care occurs when males and females cooperate to care for their joint offspring. It is associated with sexual conflict because the benefits stem from the combined effort of both parents, while any costs depend on each parent's own effort. Thus, biparental care involves a delicate balance between cooperation and conflict. Shifts in this balance are likely to be driven by environmental conditions that alter the costs and benefits to males and females. Here, we used the burying beetle Nicrophorus vespilloides to investigate whether the presence of conspecific intruders shifts the balance towards cooperation (detected as an increase in the duration of biparental care relative to uniparental care) or alters the magnitude of sex differences in care, and whether any such effects are dependent on resources available for breeding. We found that the presence or absence of conspecific intruders had no effect on the duration of biparental care relative to uniparental care. Thus, there was no evidence that the presence of intruders caused a shift towards more cooperation. Females, but not males, responded to the presence of conspecific intruders by increasing their time spent providing one form of care, but only when breeding on larger resources. Thus, there was some evidence that the presence of intruders altered the magnitude of sex differences in care and that this was conditional upon the amount of resources available for breeding. Overall, our results show that threats from conspecific intruders alters sex differences in parental care, while not changing the balance between cooperation and conflict.