A good day to die: bridging the gap between costs and benefits of parental care

Abstract

In species that provide parental care, offspring survival is often completely dependent on protection and resources afforded by the parents. Therefore, parents gain no fitness unless they raise offspring to a critical point of independence. In these species, selection should shape parental life history to increase their chances of surviving to this critical point. We test this hypothesis using females of two species of burying beetles, Nicrophorus orbicollis and N. marginatus. Burying beetles breed on small, vertebrate carcasses, and reproduction can be divided into two stages: carcass preparation and larva provisioning. Females were allowed to reproduce repeatedly until they died, and the stage in which each female died was recorded. Most females died while waiting for another carcass for their next reproductive bout or during carcass preparation, which indicates that females may have a physiological mechanism that allows them to delay death until their final brood is independent of parental care. In this paper, we show that female burying beetles of two species do not die at random times during reproduction, but instead die after they have finished caring for their offspring. This is the first time that non-random death has been shown in burying beetles. We show that females that die after offspring care is complete have a higher fitness than females that die at random because offspring in many species of burying beetles depend on parental care for food provisioning and protection. We also propose a hormonal mechanism through which females might extend their lives to allow them to finish caring for their offspring.