Tail color signals performance in blue tit nestlings

Indirect sexual selection arises when reproductive individuals choose their mates based on heritable ornaments that are genetically correlated to fitness. Evidence for genetic associations between ornamental coloration and fitness remain scarce. In this study we investigate the quantitative genetic relationship between different aspects of tail structural coloration (brightness, hue and UV chroma) and performance (cell mediated immunity, body mass and wing length) in blue tit (Cyanistes caeruleus) nestlings. In line with previous studies, we find low heritability for structural coloration and moderate heritability for performance measures. Multivariate animal models show positive genetic correlations between the three measures of performance, indicating quantitative genetic variation for overall performance while tail brightness and UV chroma, two genetically independent color measures, are genetically correlated with performance (positively and negatively respectively). Our results suggest that mate choice based on independent aspects of tail coloration can have fitness payoffs in blue tits and provide support for the indirect benefits hypothesis. However, low heritability of tail structural coloration implies that indirect sexual selection on mate choice for this ornament will be a weak evolutionary force.