Solar and terrestrial radiations explain continental-scale variation in bird pigmentation
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Animals living on the earth’s surface are protected from the damaging effects of solar ultraviolet (UV) radiation by melanin pigments that color their integument. UV levels that reach the earth’s surface vary spatially, but the role of UV exposure in shaping clinal variations in animal pigmentation has never been tested. Here, we show at a continental scale in Europe that golden eagles Aquila chrysaetos reared in territories with a high solar UV-B radiation exposure deposit lower amounts of the sulphurated form of melanin (pheomelanin) in feathers and consequently develop darker plumage phenotypes than eagles from territories with lower radiation exposure. This clinal variation in pigmentation is also explained by terrestrial γ radiation levels in the rearing territories by a similar effect on the pheomelanin content of feathers, unveiling natural radioactivity as a previously unsuspected factor shaping animal pigmentation. These findings show for the first time the potential of solar and terrestrial radiations to explain pigmentation phenotype diversity in animals, including humans, at large spatial scales.
KeywordsAnimal coloration Melanins Natural radioactivity Pigmentation UV radiation
IG is supported by a Ramón y Cajal Fellowship (RYC-2012-10237) from the Spanish Ministry of Economy and Competitiveness (MINECO). We thank Jānis Ķuze, Carl Knoff, Peter L. Pap and Gabriel Banderet for field work in Latvia, Norway, Romania and Switzerland, respectively. Metod Macek and Anton Sedlak helped with field work in Slovakia. Ulf Johansson provided us with samples from the Swedish Museum of Natural History. Rafael Márquez helped with the spectrophotometric analyses of feathers. T. Szegvary kindly allowed us to use their map of terrestrial γ-dose rates for Europe. Four reviewers commented on the manuscript.
Author contribution statement
IG conceived the study, contributed to sampling, analyzed the data and wrote the manuscript. AJ conducted the analyses of Raman spectroscopy. CP, DS, DJH, CI, JK, JTN, TO, GS and MS contributed to sampling. JJN contributed to sampling and manuscript writing.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Statement of animal rights
All applicable institutional and/or national guidelines for the care and use of animals were followed.
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