ABSTRACT
Distantly related clades that occupy similar environments may differ due to the lasting imprint of their ancestors – historical contingency. The New World warblers (Parulidae) and Old World warblers (Phylloscopidae) are ecologically similar clades that differ strikingly in plumage coloration. We studied genetic and functional evolution of the short-wavelength sensitive visual pigments (SWS2 and SWS1) to ask if altered color perception could contribute to the plumage color differences between clades. We show SWS2 is short-wavelength shifted in birds that occupy open environments, such as finches, compared to those in closed environments, including warblers. Sequencing of opsin genes and phylogenetic reconstructions indicate New World warblers were derived from a finch-like form that colonized from the Old World 15-20Ma. During this process the SWS2 gene accumulated 6 substitutions in branches leading to New World warblers, inviting the hypothesis that passage through a finch-like ancestor resulted in SWS2 evolution. In fact, we show spectral tuning remained similar across warblers as well as the finch ancestor. Results reject the hypothesis of historical contingency based on opsin spectral tuning, but point to evolution of other aspects of visual pigment function. Using the approach outlined here, historical contingency becomes a generally testable theory in systems where genotype and phenotype can be connected.
Footnotes
Additional authors: pricet{at}uchicaso.edu - Department of Ecology & Evolution, University of Chicago, 1101 E 57th Street, Chicago, IL 60637, james.morrow{at}utoronto.ca - Department of Ecology & Evolutionary Biology, University of Toronto, 25 Harbord St., Toronto, ON M5S 3G5
Data Archival Location: DNA sequences for all opsin genes sequenced here are deposited in GenBank (accession numbers KM516225-KM516272). Spectral sensitivities for all the expressed visual pigments can be found in the Electronic Supplementary Material as well as a summary of all data used in the correlated evolution tests.
