UV-induced feather color change reflects its porphyrin content

Abstract

AbstractPigmentary coloration is widespread in animals. Its evolutionary and ecological features are often attributed to the property of predominant pigments; therefore, most research has focused on predominant pigments such as carotenoids in carotenoid-based coloration. However, coloration results from predominant pigments and many other minority pigments, and the importance of the latter is overlooked. Here, we focused on porphyrin, an “uncommon” pigment found in bird feathers, and investigate its importance in the context of feather color changes in the barn swallowHirundo rustica. We found that the “pheomelanin-based coloration” of the barn swallow faded after the irradiation of UV light, and this effect was particularly strong in the feathers of young swallows (nestlings and fledglings, here). We also found that it is not the predominant pigment, pheomelanin, but protoporphyrin IX pigment that showed the same pattern of depigmentation after the irradiation of UV light, particularly in the feathers of young swallows. In fact, the abovementioned age-dependent feather color change was statistically explained by the amount of porphyrin in the feathers. The current study demonstrates that a minority pigment, porphyrin, explains within-season dynamic color change, an ecological feature of feather coloration. The porphyrin-mediated rapid color change would benefit young birds, in which feather coloration affects the parental food allocation during a few weeks before independence, but not later. Future studies should not ignore these minor but essential pigments and their evolutionary and ecological functions.Significance statementPredominant pigments are assumed to determine animal coloration and its ecological features. It is then not surprising that the evolutionary and ecological features of animal coloration are often attributed to the chemical properties of predominant pigments. However, coloration results from predominant pigments and several other minority pigments. By irradiating UV light on reddish throat feathers of the barn swallowHirundo rustica, we examined within-season dynamic color change in relation to a minority pigment, porphyrin, which has not previously been examined but is a candidate pigment for feather color change, because porphyrin can be easily photodegraded. We found that not the predominant pigment, pheomelanin, but porphyrin pigments explained the feather color change. Minor pigments and their chemical properties should not be dismissed to understand the ecological and evolutionary functions of animal coloration.