Jennifer C. Perry

Females of many species experience costs associated with mating. Seminal products, including nuptial gifts, may mitigate these mating costs or exacerbate them. For example, nuptial gifts derived from male accessory glands may transfer nutrition or potentially harmful seminal proteins to females. In this study, we assay the costs of multiple mating and the consumption of seminal products in a ladybird beetle. We compared longevity in females mated singly or multiply, while allowing or preventing spermatophore consumption at each mating. In order to distinguish a cost of mating per se from a cost of elevated reproduction, we prevented reproduction by using nutrient‐stressed females. Mating singly or multiply had no effect on female longevity, nor did spermatophore feeding influence longevity. The results imply, first, that intermediate mating rates do not directly harm females, though females may experience other indirect costs of mating (e.g. reduced foraging efficiency) or costs of reproduction; and second, that spermatophores transfer neither food nor directly harmful substances to female ladybirds.

Trophic egg‐laying – wherein mothers provide non‐developing eggs for offspring to eat – has attracted much empirical attention to diverse taxa (e.g. amphibians, non‐social and eusocial insects, fish, and marine gastropods). However, there has been been only a limited exchange of ideas among studies of different taxa. We advocate a unified approach to the study of trophic eggs within an evolutionary ecological framework. In this paper, we stress the importance of elucidating the adaptive function of trophic eggs through explicit hypothesis testing, and our primary objective is to outline key experiments that can test adaptive and functional hypotheses. Currently, some cases of hypothesized trophic eggs may simply represent offspring consumption of eggs that failed to develop for non‐adaptive reasons (e.g. sperm limitation). Furthermore, in many trophic egg‐laying species, it is unclear whether trophic eggs have evolved to provision offspring or to reduce cannibalism among offspring. With increased focus on theory and hypothesis testing, the study of trophic eggs can offer important insight into topics such as sibling rivalry, parent–offspring conflict, and parental care.

Sibling cannibalism occurs in many species, yet understanding of sibling cannibalism as an adaptation currently lags behind understanding of other antagonistic interactions among siblings. Observed sibling cannibalism phenotypes likely reflect the interaction between competitive games among siblings and parent‐offspring conflict. Using a game‐theoretic approach, we derive optimal offspring cannibalism behaviour and parental modifiers that limit or facilitate cannibalism. The results are compared to contemporary frequency‐independent analysis. With the addition of game interactions among siblings or parent‐offspring co‐evolution, our model predicts increased cannibalism (compared to the frequency‐independent prediction), as offspring compete to eat siblings. When infertile eggs are present – strengthening competition – offspring risk eating viable siblings in order to gain access to infertile eggs, intensifying parent‐offspring conflict. We use the results to make new predictions about the occurrence of sibling cannibalism. Additionally, we demonstrate the utility of trophic egg laying as a maternal mechanism to promote egg eating.