Adaptive maternal plasticity in response to perceptions of larval competition

Summary Because the developmental performance of a genotype can vary substantially depending on the conditions to which it is exposed, mothers are known to exercise strong choice concerning oviposition sites. Females potentially adjust the provisioning or paternity of offspring by responding to multiple environmental factors, but how those factors interact in the context of female assessment has been under investigated and remains poorly understood. In this study, we examine how female perceptions of the larval environment affect the size, fitness and paternity of her brood. We mated female yellow dung flies, Scathophaga stercoraria, with two different males each, manipulated female perception of larval competition levels, and subsequently split clutches across high and low-competition conditions. We found that females (especially large females) laid more eggs when they perceived low levels of competition for their brood. Females further adjusted brood size depending on the size of their last mate (who typically sires most offspring), increasing brood size for large second mates when perceiving low levels of competition, and for small second mates when they perceived competition to be high. Larval survival was highest for females who perceived the same larval conditions that their larvae experienced, and whose last mate was well suited to such conditions (e.g. small for competitive conditions, or large in the absence of competition). In contrast, the effects of competition on paternity did not depend on maternal perceptions of larval competition, as would be expected if females exercise adaptive cryptic choice to favour alternate male phenotypes depending on the intensity of larval competition. Our experimental approach supports complex and sophisticated changes in female behaviour in response to cues of larval fitness. Our results further emphasize that most plasticity in maternal behaviour serves to improve larval fitness directly, providing valuable empirical support for theoretical assertions of the primacy of material benefits over good-genes.