A pheromone that coordinates parental care is evolutionary conserved among burying beetles (Silphidae: Nicrophorus)

Abstract

Pheromones regulating mating behavior are diverse in structure and typically show high species specificity. However, depending on their information content they can also be quite conserved across species. Here, we demonstrate that methyl geranate, an anti-aphrodisiac produced during brood care, is a conserved volatile organic compound within the genus Nicrophorus (burying beetles). Burying beetles are well known for their elaborate biparental care. They reproduce on small vertebrate carcasses and typically it is a pair of beetles, a male and a female, which cooperate in feeding and defending their young. During the intensive period of parental care, female Nicrophorus vespilloides have been shown to emit a volatile substance, methyl geranate, which acts as an anti-aphrodisiac and deters males from copulating. Methyl geranate is biosynthetically linked to juvenile hormone III, a hormone mediating a temporary infertility in this species. By investigating volatile emission of seven geographically and phylogenetically distinct burying beetle species, we provide evidence that methyl geranate is a conserved substance released by parenting adults throughout the genus. We, furthermore, show that there is high quantitative variation (1) between species, which can partly be explained by species differences in body size and (2) within species, which can be attributed to sex differences and individual brood size differences. Moreover, we demonstrate that a species of the genus Ptomascopus, which is closely related to Nicrophorus, but shows no elaborate post-hatching parental behavior, emits only trace amounts of methyl geranate during breeding. Our results, therefore, suggest that the synthesis of an anti-aphrodisiac was an important step in the evolution of concerted parental care in burying beetles. However, behavioral experiments are needed to further corroborate our hypothesis.