Parental care trade-offs and the role of filial cannibalism in the maritime earwig, Anisolabis maritima

Abstract

Animals that provide parental care are expected to weigh the value of current offspring against the value of future offspring, such that total investment across all offspring is allocated to maximize lifetime fitness. In this study, we characterize the trade-offs associated with maternal care in the maritime earwig, Anisolabis maritima (Dermaptera: Anisolabididae). We measured the benefits of care in terms of hatching success through removal experiments and the costs of care by comparing the future fecundity of caring females to that of removals. We show that the benefits of care greatly outweigh the costs, providing a seven-fold increase in hatching success. Artificially removed females had larger subsequent clutches and shorter internest intervals, but very low hatching success. Naturally abandoning females always cannibalize all their eggs. Partial clutch cannibalism was a ubiquitous feature of maternal care, although rates were variable among individuals. In post hoc tests, we first addressed the ultimate explanation that filial cannibalism is a way for females to facultatively adjust their investment per clutch in order to maximize future reproduction. We then tested two proximate explanations for filial cannibalism: (1) females that lay more eggs for their given body size tend to consume more eggs, reflecting a nutritional deficiency; (2) females prefer to cannibalize the youngest eggs to reduce the overall duration of egg care. In addition, we consider the alternative explanation that females eat unviable eggs for hygienic reasons. Our results provide support for both energy limitation and hygienic maintenance. Higher rates of egg cannibalism near the very end of nesting were also suggestive of nymphal cannibalism, a phenomenon that will be examined in future work.