title: Social huddling and physiological thermoregulation are related to melanism in the nocturnal barn owl.
abstract: Endothermic animals vary in their physiological ability to maintain a constant body temperature. Since melanin-based coloration is related to thermoregulation and energy homeostasis, we predict that dark and pale melanic individuals adopt different behaviours to regulate their body temperature. Young animals are particularly sensitive to a decrease in ambient temperature because their physiological system is not yet mature and growth may be traded-off against thermoregulation. To reduce energy loss, offspring huddle during periods of cold weather. We investigated in nestling barn owls (Tyto alba) whether body temperature, oxygen consumption and huddling were associated with melanin-based coloration. Isolated owlets displaying more black feather spots had a lower body temperature and consumed more oxygen than those with fewer black spots. This suggests that highly melanic individuals display a different thermoregulation strategy. This interpretation is also supported by the finding that, at relatively low ambient temperature, owlets displaying more black spots huddled more rapidly and more often than those displaying fewer spots. Assuming that spot number is associated with the ability to thermoregulate not only in Swiss barn owls but also in other Tytonidae, our results could explain geographic variation in the degree of melanism. Indeed, in the northern hemisphere, barn owls and allies are less spotted polewards than close to the equator, and in the northern American continent, barn owls are also less spotted in colder regions. If melanic spots themselves helped thermoregulation, we would have expected the opposite results. We therefore suggest that some melanogenic genes pleiotropically regulate thermoregulatory processes.
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland. amelie.n.dreiss@gmail.com.|Institute of Ecology and Evolution, University of Bern, Bern, Switzerland. amelie.n.dreiss@gmail.com.
authors.forename: Amélie N
authors.initials: AN
authors.lastname: Dreiss
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Robin
authors.initials: R
authors.lastname: Séchaud
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Paul
authors.initials: P
authors.lastname: Béziers
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.|UMR 7179 CNRS, Museum National d'Histoire Naturelle, Brunoy, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Villain
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Genoud
authors.affiliation: Swiss Ornithological Institute, Sempach, Switzerland.
authors.forename: Bettina
authors.initials: B
authors.lastname: Almasi
authors.affiliation: Swiss Ornithological Institute, Sempach, Switzerland.
authors.forename: Lukas
authors.initials: L
authors.lastname: Jenni
authors.affiliation: Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Roulin
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000235:genetics / Q000502:physiology*; D003080:Cold Temperature; D005241:Feathers / Q000502:physiology; D008543:Melanins; D008548:Melanosis / Q000235:genetics; D020305:Strigiformes / Q000235:genetics / Q000502:physiology*
chemical_list: D008543:Melanins
keywords: Huddling; Melanin; Metabolic rate; Oxygen consumption; Pleiotropy; Temperature; Thermoregulation