Nutritional and Social Environmental Effects on Parental Care

Parental care is likely to evolve when benefits of care are greater than costs. Provision of parental care may buffer vulnerable offspring against unpredictable or hazardous environments permitting parents to breed in situations too hostile for unassisted juvenile survival. The nature of environmental unpredictability faced by parents and their offspring (e.g., availability of nutritional resources, breeding resources and/or the strength of competition) provides the ecological context in which costs and benefits of parental traits are defined. Therefore investigations about how the environment might shape parental traits ought not only to be conducted in the laboratory but also in a natural setting where unanticipated parameters may have profound effects on theoretical predictions. I conducted a series of manipulative experiments and observational studies in the laboratory and in the field using burying beetles, Nicrophorus vespilloides, to examine the effects of environmental variation on parental competitive ability, reproductive productivity, longevity and the expression of parental sex-role differences and alternative reproductive tactics. In these beetles a relative size advantage confers success in contests for scarce and vital breeding resources so a central prediction was that reproductive success would be positively correlated with body size. In contrast I found that reproductive performance was favoured over contest success when nutritional resources were delayed temporarily during a developmental window. Larger beetles do win contests for breeding-resources but the benefits of being large depend on the quality of the social environment experienced (i.e., the relative size of an opponent). In a naturalistic setting, smaller males avoided direct contests because they attracted proportionately more females and as a result their breeding associations were more often monogamous. This has potential benefits for females because they avoid female-female contests and brood parasitism. Variation in the nutritional environment provided by parents (the carcass size on which offspring are reared) directly influences body size creating a dynamism between the nutritional and social environments experienced by these beetles depending on their size, which has ramifications for their individual success and maintenance of alternative strategies in the population as a whole.