Meeting Abstract
Competitive interactions between females can result in permanent behavioral and physiological programming of offspring via hormone-mediated maternal effects. For birds, exposure to increased competition generally causes greater deposition of testosterone into their egg yolks. Increased yolk testosterone programs offspring to grow faster and be more aggressive, traits that appear beneficial for high-competition environments. Nevertheless, not all studies show a positive relationship between competition and yolk testosterone, and these studies are generally labeled as anomalies. However, if we address these studies from a species-specific context, rather than assuming a uniform “ideal” phenotype for a given environment, we may find that alternative allocation patterns of yolk testosterone in response to competition create phenotypes that are likewise beneficial. Transient changes in competition (e.g., breeding density) may elicit a hormonal response, but there are also other inherent, species-specific traits (e.g., solitary vs colonial breeders) that generate differences in competition and likely provide selection pressures that shape this response. To test this idea, we performed a meta-analysis using effect size of yolk testosterone allocation in response to competition. We used species-specific traits to account for inter-specific variation in yolk testosterone response and found that effect size was significantly moderated by several traits, in particular, coloniality. Applying a species-specific perspective helps contextualize studies that show little or negative response of yolk testosterone to competition and improves our understanding of how variation in this response evolved.
