Hormonal regulation of offspring begging and mediation of parent–offspring conflict

Abstract

Recently, there has been much interest in the role of endogenous and maternal hormones as regulators of offspring begging and mediators of parent-offspring conflict. Here, we review recent work in this field, and identify inconsistencies in the literature. We find good evidence that hormones play a role as regulators of begging: 13 studies report a positive effect on begging and six a negative effect. There is also good evidence that hormones influence offspring fitness, but the direction of reported effects is inconsistent: eight studies report a positive effect on offspring fitness and 10 a negative effect. We explore potential pathways linking hormonal effects on begging and growth. We find that our current understanding of these pathways is incomplete, and suggest a simple model linking hormonal effects on begging and growth. We next discuss the role of hormones as mediators of parent-offspring conflict. We find little evidence that maternal hormones provide a mechanism for parental favouritism. We use graphical models to explore the hypothesis that maternal hormones act as honest signals, and find that costs of hormone production can ensure the honesty of maternal hormones but only under very restricted conditions. We discuss evidence from recent cross-fostering experiments suggesting that maternal hormones act in the context of overlapping interests between parents and offspring. Finally, we highlight the need for more studies on nonavian taxa to establish whether hormonal regulation of begging is specific to birds or general across taxa where offspring beg for food from their parents.