Meeting Abstract
20.1 Saturday, Jan. 4 13:30 Differential high-altitude adaptation and limited gene flow across a mid-elevation hybrid zone in birds DUBAY, SG*; WITT, CC; Univ. of Chicago; Univ. of New Mexico dubaysg@uchicago.edu
The Andes are a global hotspot of biological diversity that is characterized by dramatic elevational shifts in community composition and a preponderance of recently evolved species. Animal habitats in the Andes span a ~5000 m elevational gradient, encompassing a tremendous range of atmospheric conditions that pose challenges for respiration, thermoregulation, and water balance. Few studies address the extent to which this elevational gradient influences speciation or facilitates high rates of species turnover. We report a previously unknown hybrid zone between recently diverged flycatchers (Aves: Tyrannidae) with partially overlapping elevational ranges. The southern Anairetes reguloides has a broad elevational distribution from 0-4200 m, while the northern Anairetes nigrocristatus is restricted to elevations above 3000 m. Where the two species overlap in central Peru we found hybrids at elevations between ~3100-3800 m, with A. nigrocristatus above this elevation and A. reguloides below. We analyzed variation in hematological parameters, morphology, and unlinked genetic markers across an elevational transect encompassing the hybrid zone. The hybrid zone was structured as a steep cline, with little evidence of gene flow away from the two central, mid-elevation localities of the transect. Relative heart mass and hemoglobin concentration increased strikingly with elevation and the proportion of genetic input from A. reguloides, suggesting that the latter species is not genetically adapted to high altitudes. A. nigrocristatus did not show evidence of respiratory stress at high altitudes. These results suggest a physiological basis for elevational replacement and species turnover across elevational gradients, whereby differential adaptation to altitude maintains the distinctness of incipient species by stable parapatry along an elevational contour.
