Condition-dependence of pheomelanin-based coloration in nuthatches Sitta europaea suggests a detoxifying function: implications for the evolution of juvenile plumage patterns

摘要

Adult-like juvenile plumage patterns often signal genotypic quality to parents. During adulthood, the\udsame patterns often signal quality to mates. This has led to assume that adult-like juvenile plumage\udis a developmental consequence of sexual selection operating in adults. Many of these patterns are\udproduced by the pigment pheomelanin, whose synthesis may help remove toxic excess cysteine.\udExcess cysteine is likely to arise under conditions of relatively low stress, such as those experienced by\udnestling birds. Thus, adult-like plumage may be advantageous for juveniles if produced by pheomelanin.\udIn the Eurasian nuthatch Sitta europaea, juveniles are sexually dichromatic and identical to adults.\udNestling nuthatches in poorer condition develop more intense pheomelanin-based feathers, indicating\udgreater pigment production. The same is not observed in adults. This is contrary to a function related\udto signaling quality and instead suggests that, at least in the Eurasian nuthatch, adult-like juvenile\udplumage has evolved because of the detoxifying function of pheomelanin-based pigmentation.\udGiven the prevalence of colors typically conferred by pheomelanin in juvenile plumage patterns, the\uddetoxifying capacity of pheomelanin under low stress levels should be considered as an explanation for\udthe evolution of both adult-like and distinctively juvenile plumage patterns