Sex differences in parental defence against conspecific intruders in the burying beetle Nicrophorus vespilloides

In species with biparental care, females often provide more care than males. Previous work has focused on sex differences in parental food provisioning and defence against predators. However, parents often also defend their offspring against conspecific intruders, which could be male or female. Thus, there is a need for studies examining sex differences in the behaviour of both caring parents and intruders, and whether sex differences in the behaviour of caring parents depend upon the intruder's sex. We conducted an experiment on the burying beetle Nicrophorus vespilloides where a single female or male resident caring for a brood was confronted with a male or female intruder. Female residents were more successful in defending their brood and engaged in more fights against an intruder than males. Residents engaged in more fights against male intruders and, among those that successfully defended their brood, residents spent more time provisioning food to larvae when confronted with female intruders. There was no evidence that sex differences in the behaviour of caring parents depended upon the intruder's sex. There were no sex differences in any measures of reproductive success among those residents that successfully defended their brood and no sex differences in the life span or mass gain of either residents or intruders. Our study extends the study of sex differences in parental care to the context of defence against conspecific intruders by demonstrating sex differences in the behaviour of both residents and intruders and sex differences in reproductive success in the presence of conspecific intruders.