Resource concealment and the evolution of parental care in burying beetles

Comparative experimental study of species can provide insight into behavioral transitions in evolution. The insects offer many such examples for the analysis of parental care. We examined three distantly related species of Nicrophorus and two non-Nicrophorus silphid beetles for their ability to conceal odors from a carcass that cue competitors that attempt to usurp the resource. We predicted that species with well-developed parental care would exhibit a heightened ability to conceal a resource from competitors, even when differences in burying behavior and direct defense were experimentally eliminated. Carcasses were provided to male-female pairs in the laboratory for 3 days and then experimentally buried in the field, without parents, to assess discovery by Nicrophorus and vertebrate scavengers. The burying beetles Ni. orbicollis, Ni. sayi and Ni. pustulatus were far more successful in hiding a prepared resource (>76%) from free-flying Nicrophorus than the less parental Ptomascopus morio or Necrophila americana (<25%). Carcasses provided to P. morio and Ne. americana were also more likely to be discovered by Nicrophorus than non-prepared control carcasses, suggesting that microbially derived odor cues available to competitors were increased by non-Nicrophorus interaction with carcasses. In the absence of burial, carcass preparation had no effect on vertebrate scavenging. We hypothesize that the evolution of burying and carcass modification to conceal a discovered resource from diverse competitors, more so than control of microbial decay, was a critical step in the evolutionary transition to monopolization of a small carcass, nesting and extended parental care in the Silphidae.