Morphological differences in a population of Rufous-collared Sparrow (Zonotrichia capensis, Statius Müller, 1776) (Passerine, Emberizidae) at different elevations in the Tropical Andes

Abstract

Populations that breed along steep elevation gradients show diverse physiological and morphological changes in response to the different environmental conditions. The latter has been discussed by Bergmann’s and Allen’s ecogeographic rules about body and appendage sizes and environmental temperature. We compared morphometric measures (mass, bill width, tarsus, wing, and tail length) of a Zonotrichia capensis population in two localities at different elevations with similar latitudes and photoperiods on the western slope of the Colombian Central Andes. We compared a Low Elevation locality (LE) at 1800 m a.s.l. and a High Elevation locality (HE) at 3853 m a.s.l. that have approximate wind speeds of 1.3 m/s and 8.4 m/s, respectively. During 12 months of sampling, we captured 46 adults using mist-nets; 26 in the LE and 20 in the HE. Each individual was sexed using molecular techniques at the Laboratory of Genetics of the Department of Biological Sciences of Universidad de Caldas. Individuals (males + females) from the HE had longer wings and tails than those from the LE (F1,44 = 5.93; P = 0.019). Also, wings of males in the HE were longer than those of females in both localities and tails of males in the HE were longer than those of LE males. Our results did not agree with what was expected according to Allen’s and Bergmann’s ecogeographic rules. Longer wings and tails increase sustainment, maneuverability, and balance in low atmospheric pressures and strong air currents and these conditions are found at high elevation habitats. Most likely, the longer wings found for HE males allow greater movement during territorial behavior. Further, these differences in morphological traits along elevational gradients could result from micro-evolutionary changes between localities or phenotypic plasticity of individuals exposed to different environmental conditions.

Breeding biology in a population of Rufous-collared Sparrow (Zonotrichia capensis, Statius Müller, 1776) at different elevations in the Tropical Andes

“…), are separated in a straight line by 26 km. Despite their proximity, these sites have different climate conditions (Busi et al 2020). The LE locality is located in a coffee growing region with an average annual temperature of 20.7ºC (min.…”

Color and morphological differentiation in the Sinaloa Wren (Thryophilus sinaloa) in the tropical dry forests of Mexico: The role of environment and geographic isolation

“…tarsus and culmen) in cooler climates in order to minimize heat loss [ 15 ]. However, other factors have also been suggested to influence phenotypic variation; for instance, longer wings and tails have been positively associated with higher elevations where low atmospheric pressures and strong air currents prevail [ 16 – 18 ], which helps to increase flight efficiency, as well as contributing to balance and lift [ 19 , 20 ]. Moreover, environmental variables such as precipitation could impact habitat characteristics such as understory density and overall forest interior structure [ 21 ], which can influence tarsus, wing and tail morphology since these traits are respectively related to foraging, flight performance and maneuverability [ 22 – 24 ].…”