Multiple sexual ornaments signal heterozygosity in male blue tits

Higher individual genetic quality has been hypothesized to be associated with the expression of conspicuous ornaments. However, the relationship between multicomponent sexual signals and heterozygosity is poorly understood. In this study, we examined whether different ornaments, including song (repertoire size and bout length) and plumage coloration (yellow breast and blue crown), reflect individual genetic diversity in male blue tits (Aves: Cyanistes caeruleus). We estimated genetic diversity using 26 microsatellite markers that were classified as putatively functional (12 loci) and neutral (14 loci). We found that yellow breast carotenoid chroma, blue crown brightness, bout length and body condition were positively associated with heterozygosity at functional loci, but not with genetic diversity estimated at all typed loci or the subset of neutral markers. The lack of strong single-locus effects and the presence of identity disequilibrium in our population suggest that the observed heterozygosity-phenotype associations are driven by loci widely distributed across the genome. The predominant role of putatively functional loci evidences that the expression of secondary sexual characters is more tightly reflected by heterozygosity at genomic regions containing coding genes that are being actively expressed, a fact that may make ornamental traits more reliable indicators of the genetic quality of individuals. Overall, this study shows that multiple secondary sexual characters reflect male genetic diversity and lends support to the good-genes-as-heterozygosity hypothesis