Assessing the association between animal color and behavior: A meta-analysis of experimental studies

Color varies in pattern and degree across the tree of life. In animals, genetic variation in color is hypothesized to have pleiotropic effects on a variety of behaviors, due to shared dependence on underlying biochemical pathways. Such pleiotropy can constrain the independent evolution of color and behavior. Although associations between color and behavior have been reported, this relationship has not yet been addressed across a broad taxonomic scale with a formal meta-analysis. We used a phylogenetic meta-analytic approach to examine the relationship between individual variation in aggressive behavior and variation in multiple colors. Seventy-four studies met our inclusion criteria (vertebrates = 70; invertebrates = 4). After accounting for phylogeny and correcting for publication bias, there was a positive association between measures of aggression and degree or area of coloration (mean = 0.248, 95% CI = (0.044, 0.477)). Because this positive association was not restricted to melanin-based coloration, we conclude that this pattern does not strongly support the melanin-pleiotropy hypothesis. Because the association was also not affected by moderators accounting for individual condition, social rank, or age, the results do not strongly support hypotheses that condition dependence accounts for relationships between color and aggressive behavior. The badge of status hypothesis predicts that arbitrary traits can evolve to signal aggression or social dominance. We propose that this is the most parsimonious explanation for the patterns we observe. Because of lack of evidence for condition dependence in the association between color and aggression, we further propose that the genetic covariation between traits contributes to the evolution of the badges of status.