Stress and sexual signaling: a systematic review and meta-analysis

The vertebrate stress response has been shown to suppress investment in reproductive and immune function and may also lead to a reduced investment in the production of secondary sexual traits. However, it has been difficult to model roles of stress in sexual selection due to the inconsistent results seen in empirical studies testing for the effect of stress on the expression of secondary sexual traits. We conducted a phylogenetically controlled meta-analysis of published associations between physiological correlates of stress and sexual signaling in vertebrates in order to identify any consistent patterns. Our analysis included signaling in both males and females, 4 stress measures, and 4 categories of sexually selected traits (vocalizations, traits that varied in size, traits that varied in coloration, and opposite-sex preference). Across 38 studies of 26 species, there was no significant relationship between physiological correlates of stress and the expression of sexual signals. Mean effect size, however, varied significantly across the 4 types of sexually selected trait. We propose development of a model that incorporates the nuanced effects of species ecology, trait type, ecological context, and the complex nature of the physiological stress response, on the expression of sexually selected traits.