Meeting Abstract
Altricial young are not capable of securing food for themselves, and must solicit feeding from parents. The ability of an individual to outcompete its siblings for this parental provisioning is, therefore, integrally related to its future reproductive potential. Several adaptations may be beneficial to young animals in this regard. For example, large size relative to siblings may promote success in sibling competition and draw increased provisioning from parents. Similarly, aggression may increase success in this context. However, the physiological mechanisms underpinning effective sibling rivalry are not well understood. Sibling rivalry may be hormonally mediated. Hormonally mediated traits such as rapid growth could provide an advantage in scramble competitions such as those exhibited by altricial birds. In this study, we analyzed the effects of the peptide hormone insulin-like growth factor 1 (IGF-1) on markers of sibling rivalry in Eastern Bluebirds (Sialia sialis) and assessed the ability of nestlings to adaptively modulate levels of this hormone in response to brood size. Free-living bluebird nestlings were cross-fostered in order to artificially modify brood size, body measurements were taken, and endogenous IGF-1 levels were quantified. In a subsequent experiment, exogenous IGF-1 was administered to nestlings in order to elucidate its effects on body size and behavior. This study has the potential to contribute to our understanding of both sibling rivalry and hormonal plasticity.
