Down Feather Structure Varies Between Low- and High-Altitude Torrent Ducks (MerganettaArmata) in the Andes

Abstract

Feathers are one of the defining characteristics of birds and serve a critical role in thermal insulation and physical protection against the environment. Feather structure is known to vary among individuals, and it has been suggested that populations exposed to different environmental conditions may exhibit different patterns in feather structure. We examined both down and contour feathers from two populations of male Torrent Ducks (Merganetta armata) from Lima, Peru, including one high-altitude population from the Chancay-Huaral River at approximately 3500 meters (m) elevation and one low-altitude population from the Chillón River at approximately 1500 m. Down feather structure differed significantly between the two populations. Ducks from the high-altitude population had longer, denser down compared with low-altitude individuals. Contour feather structure varied greatly among individuals but showed no significant difference between populations. These results suggest that the innermost, insulative layer of plumage (the down), may have developed in response to lower ambient temperatures at high elevations. The lack of observable differences in the contour feathers may be due to the general constraints of the waterproofing capability of this outer plumage layer.ResumenEl plumaje es una característica que define a las aves y cumple roles críticos en el aislamiento térmico y protección física del ambiente. Se sabe que la estructura de las plumas varía ente individuos, y se ha sugerido que poblaciones expuestas a diferentes condiciones ambientales pueden exhibir diferentes patrones en la estructura de las plumas. En este estudio se examinaron tanto el plumón como las plumas de contorno de machos adultos del Pato de los Torrentes (Merganetta armata) de dos poblaciones, una en el río Chancay-Huaral a 3,500 msnm y otra en el río Chillón a 1,500 msnm, ubicadas en Lima, Perú. La estructura de los plumones difiere significativamente entre las dos poblaciones. Los patos de la población a grandes elevaciones tienen plumones largos, y densos comparados con los individuos de las partes bajas. La estructura de las plumas de contorno varía ampliamente entre individuos pero no muestra diferencias significativas entre poblaciones. Estos resultados sugieren que las diferencias entre las capas interiores de aislamiento del plumaje (plumón), haberse desarrollado como respuesta en ambientes de bajas temperaturas a grandes elevaciones. En cambio la falta de detectables diferencias en las plumas de contorno puede ser debido a la constante selección en la capacidad impermeable de la capa de plumas exteriores.

Down feather morphology reflects adaptation to habitat and thermal conditions across the avian phylogeny

“…This is a key characteristic for ensuring better air trapping capacity (Fuller 2015;D'Alba et al 2017) and, hence, insulation in strong winds. In line with this, previous work shows that harsher wintering temperatures is associated with longer plumulaceous sections of contour feathers both across (Pap et al 2017) and within bird species (Cheek et al 2018). Similar adaptations have been found in mammals, at least in the sense that the insulating values of the fur in Arctic mammals was found to be proportional to the length of the hairs (Scholander et al 1950).…”

“…2017) and within bird species (Cheek et al. 2018). Similar adaptations have been found in mammals, at least in the sense that the insulating values of the fur in Arctic mammals was found to be proportional to the length of the hairs (Scholander et al.…”

Old divergence and restricted gene flow between torrent duck (Merganetta armata) subspecies in the Central and Southern Andes

“…Thus, the physiological restriction imposed by hypoxia at elevations >2,500 m appears to not constrain mitochondrial gene flow between low-and high-altitude localities on any of the rivers we sampled, despite recently reported elevational variation in body size(Gutiérrez-Pinto et al, 2014), function of key enzymes(Dawson et al, 2016), changes in insulative properties of feathers(Cheek et al, 2018), and changes in the hypoxic ventilatory response(Ivy et al, 2019). Thus, the physiological restriction imposed by hypoxia at elevations >2,500 m appears to not constrain mitochondrial gene flow between low-and high-altitude localities on any of the rivers we sampled, despite recently reported elevational variation in body size(Gutiérrez-Pinto et al, 2014), function of key enzymes(Dawson et al, 2016), changes in insulative properties of feathers(Cheek et al, 2018), and changes in the hypoxic ventilatory response(Ivy et al, 2019).…”

“…These direct observations of altitudinal movements corroborate the absence of population structure along elevation gradient within each river. Thus, the physiological restriction imposed by hypoxia at elevations >2,500 m appears to not constrain mitochondrial gene flow between low-and high-altitude localities on any of the rivers we sampled, despite recently reported elevational variation in body size(Gutiérrez-Pinto et al, 2014), function of key enzymes(Dawson et al, 2016), changes in insulative properties of feathers(Cheek et al, 2018), and changes in the hypoxic ventilatory response(Ivy et al, 2019).…”

“…Finally, this genetic characterization across altitudinal gradients permits us to explore whether genetic variation is associated with recently described morphological and physiological differences of torrent ducks at high elevations, including changes in body size (Gutiérrez-Pinto et al, 2014), function of key enzymes (Dawson et al, 2016), changes in insulative properties of feathers (Cheek, Alza, & McCracken, 2018), and changes in the hypoxic ventilatory response (Ivy et al, 2019).…”