Male pheomelanin pigmentation and breeding onset in Barn Swallows Hirundo rustica gutturalis

Abstract

Plumage color is a composite trait and each component can provide information regarding individual quality. Melanin-based color is one of the most common plumage coloration in birds. This color comprises two types of melanin pigments: eumelanin (black pigment) and pheomelanin (yellow-reddish pigment), and it is affected by several post-molting processes such as UV damage, staining, and preen oils. In some birds, pheomelanin-based plumage color is related to several measures of sexual selection; however, pheomelanin is almost always expressed together with eumelanin and affected by post-molting processes. Therefore, it is still unclear whether (and to what extent) pheomelanin can explain the observed relationship between plumage color and the measure of sexual selection. Here we examined the melanin (both eumelanin and pheomelanin) concentration in relation to breeding onset, as a fitness component associated with sexual selection in male Barn Swallows (Hirundo rustica gutturalis). We found that throat feathers in males contained more pheomelanin than those in females. The amount of pheomelanin, but not eumelanin, declined throughout the sampling period, indicating that pheomelanin pigmentation conveys different information than eumelanin. Even after correcting for depigmentation of melanin, males with more pheomelanin bred earlier than the others. Together with the results from previous studies, these findings indicate that pheomelanin-based coloration may have evolved via sexual selection for pheomelanin pigmentation in Barn Swallows.