Access to a carcass, but not mating opportunities, influences paternal care in burying beetles

Abstract

Selection should favor greater parental effort when the caring individual is more likely to be related to the offspring in its care. If certainty of paternity varies across broods, plasticity in the extent of paternal care may be advantageous, provided that cues of a male’s paternity are available. Consequently, to understand relationships between parentage and parental care, it is necessary to identify the proximate factors governing the decision of males to provide care. Here, we examined parental decision rules in burying beetles, Nicrophorus vespilloides, carrion breeders exhibiting elaborate biparental care. In this species, aggressive interactions that ensue upon the discovery of a carcass by more than one male usually result in a single dominant male that monopolizes access to the carcass and the resident female, relegating subordinates to sneak matings. In the current study, we removed the dominant male after the larvae had hatched and found that about half of the subordinates opted to care for the brood. The decision to provide care was affected by carcass size and the presence of the resident female during the post-hatching period. In a second experiment, we manipulated a subordinate’s access to the resident female and/or the carcass during the pre-hatching period. Surprisingly, we found that mating opportunities had no effect on the subordinate’s decision to provide care. Instead, it was the opportunity to access the carcass that triggered male parental behavior. Our results highlight the need for careful experimental manipulations to identify the cue(s) used by males to assess their certainty of paternity.

Significance statement

Theory predicts that low confidence of paternity should favor a reduction in male parental care. However, empirical studies provide only mixed support for this tenet. A deeper understanding of the relationship between paternity assurance and parental care requires an understanding of the proximate mechanisms governing a male’s decision to care. Burying beetles reproduce on dead vertebrates and are known for their elaborate biparental care. We discovered, unexpectedly, that a male’s decision to care did not depend on his opportunities to mate with the resident female, but rather, on his opportunities to access the carcass. Males given access to the breeding resource cared for young even though they had been denied access to the resident female. Thus, deciphering the cues triggering parental behavior may reveal a “rule of thumb” that explains why paternal care can become unlinked from a male’s paternity.