Is black plumage an adaptation to high elevations in a cosmopolitan bird genus?

Abstract

Black plumage is expected to absorb and retain more heat and provide better protection against UV radiation compared with lighter plumages. Black plumage is common in species of the genera Turdus and Platycichla that inhabit highlands across different regions of the world. Considering this geographical recurrent pattern we tested the hypothesis that black plumage in these two genera has evolved as a co-adaptive response to inhabiting highlands, reconstructing ancestral character states for plumage and altitudinal distribution using maximum-likelihood methods, and a Pagel’s multistate discrete method. For these analyses, we used a phylogeny based on mitochondrial and nuclear DNA regions that included 60 of the 66 recognized species in the genera Turdus and Platycichla. We found that black-plumage coloration evolved independently on eight occasions within these two genera, and species with black plumage occur more often at highlands. Our results support the hypothesis that black-plumage is adaptative in highlands; but, studies in other bird groups with blackplumage inhabiting at the same elevations will provide evidence for this adaptive hypothesis or if the evolution of black-plumage in other groups is explained by other evolutionary forces.