Island volcanism predicts pheomelanin‐based plumage colouration in a cosmopolitan raptor

Abstract

AimPheomelanin is a pigment responsible for yellowish‐to‐reddish colours of vertebrate teguments. Its biosynthesis is favoured under high concentration of intracellular thiols, which, in turn, can depend on the environmental exposure to sulphur. Thus, pheomelanin production should be more intense and frequent in environments characterized by high level of sulphur, such as volcanic regions. In this study, we aimed at addressing this hypothesis by investigating variation in plumage colour of insular populations of the cosmopolitan barn owl (Tyto alba species complex) according to the presence of soils of volcanic origin (i.e. andosols) and recent volcanic activity.LocationWorld.TaxonBarn owl species complex.MethodsWe measured plumage colouration of more than 2000 museum specimens from 50 islands and archipelagos worldwide. We then compared plumage colouration between populations living on volcanic (i.e. where andosols and/or recent volcanic activity are present) and non‐volcanic islands/archipelagos.ResultsConsistently with the prediction, plumage colouration is significantly darker (i.e. pheomelanic) on islands/archipelagos where andosols and/or recent volcanic activity are present than absent, although this environmental factor explains a small fraction of plumage colour variability across islands (<10%). Similar results were obtained when specimens' sex and climatic predictors were included in the analyses.Main ConclusionsBecause excessive intracellular levels of thiols can be toxic, pheomelanin synthesis may function as a mechanism keeping these compounds below the toxicity threshold and limiting their detrimental effects on physiology. Darker plumage may also be favoured because it promotes background matching against the dark environment typical of volcanic islands (dense vegetation cover and/or dark soil). Our results add to the little evidence that the environmental exposure of compounds that are involved in melanin biosynthesis can affect animal pigmentation and suggest that soil composition may be a factor that affects melanogenesis, possibly contributing to generate spatial variation in pheomelanin‐based traits in animals.

Rodents show darker and redder coloration in warm and rainy environments

“…Despite numerous proposed mechanisms for eumelanic color variation (see above), the underlying mechanism influencing pheomelanic phenotypes remains unknown (Delhey, 2019; Marcondes et al., 2021). The original explanation suggests that warmer and drier environments may select yellowish or reddish‐brown colors to enhance background matching (Delhey, 2019; Romano et al., 2023; Singaravelan et al., 2010). Although our findings offer some support for this idea, the increased redness observed in rainy areas still lacks a clear explanation.…”

Volcanoes, evolving landscapes, and biodiversity in Neotropical mountains

“…The spatial distribution of andosols may also foster patterns in phenotypic variation across space via adaptation or phenotypic plasticity. For example, plumage coloration in populations of Barn Owls (Tyto alba) is darker in areas where andosols are present or recent volcanic activity has occurred, a pattern attributable to greater production of phaeomelanin due to adaptation to darker soil surfaces (background matching) or to the influence of sulfur on metabolic pathways involved in pigment synthesis (Romano et al 2023).…”