Sex-dependent integration of ornamentation, personality, morphology, and life history

Phenotypic integration can be defined as the patterns and strength of the covariances between traits in an organism. The pace of life syndrome (POLS) hypothesis provides a testable case of phenotypic integration as it predicts that traits that mediate the trade-off between current and future reproduction should have coevolved with the slow-fast life-history continuum and may thus covary across individuals of a population. Although the POLS hypothesis has received increasing attention over the last decade, there is a need for investigating whether POLS are sex-specific and whether ornamental traits can be included within the POLS framework. We used 9 years of data to describe the integration patterns of ornamental coloration, personality, morphology, and life history in blue tits (Cyanistes caeruleus) and whether they differed between males and females. With that aim, we fitted multivariate mixed models separating the among- from the within-individual covariances. We found that the overall integration between the studied traits was weak, but our results suggested some sex-specific covariances at the among- and within-individual levels. Finally, using structural equation models (SEM), we tested for the presence of trait modules (i.e., covariances between traits involved in the same biological function) within each sex. SEMs suggested the presence of a morphological module but no modules for coloration or behavioral traits. Also, results obtained from the SEM did not support the POLS hypothesis. Overall, this work highlights the importance of considering sex when studying phenotypic integration and the relevance of SEM to test POLS hypothesis. Analyzing how traits measured on living organisms covary is an important step to understand their evolution. Here, we used nine years of data to analyze if the association between behavior, ornamentation, morphology, and life history differs between male and female blue tits. Our results showed weak associations between traits, mainly involving the ornaments and behavior, and they differed between the sexes. The results highlight the importance of considering sex when exploring association between traits.