Regulation of brood size by male parents and cues employed to assess resource size by burying beetles

Abstract

Burying beetles prepare small vertebrate carcasses as a resource for their young and adjust the size of their brood to match the size of the resource. We tested whether single males of N. orbicollis can regulate brood size in the absence of clutch or brood size adjustments by females, and whether parents use mass- or volume-related cues to estimate resource potential. When provided with 25 first instar larvae, single males reared significantly more young on larger carcasses than on smaller carcasses (18.5 versus 11.4). Mortality of young occurred almost exclusively during the early stages of parental care, and therefore was unrelated to depletion of the resource. The mean mass of individual larvae at dispersal did not vary with resource size, and was consistent with 15 previous experiments utilizing N. orbicollis, suggesting that regulation of brood size had occurred. Examination of previous experiments also suggested that the number and mean mass of young was not affected by whether one or two parents provide care. Mass and volume of carcasses were manipulated to examine possible cues that burying beetles might employ to assess resource size. The addition of lead weights into the body cavity of a mouse corpse (mean increase in mass of 64%) did not alter the number of young produced by male-female pairs. When volume of a corpse was experimentally increased using hollow plastic tubes (mean increase of 21%), however, pairs reared 17% more offspring than on control carcasses. Mean mass of individual offspring on volume-enhanced carcasses was significantly less (– 18%) than on control carcasses. This suggests that burying beetles use a volume- but not a mass-related cue to assess resource potential. We also present evidence that increased handling time of a carcass during nest preparation may lead to deterioration in resource quality.