Sequence Variation in the Melanocortin-1 Receptor (MC1R) Does Not Explain Continent-wide Plumage Color Differences in the Australian Magpie (Cracticus tibicen)

The genetic basis of plumage color variation has already been determined for many model species; however, the genetic mechanisms responsible for intraspecific color variation in the majority of wild-bird species are yet to be uncovered. The Australian magpie (Cracticus tibicen) is a large black and white passerine which is widely distributed across the Australian continent. The proportion of melanized back plumage varies between regionally delineated subspecies; where back-color forms overlap, intermediate color phenotypes are produced. This study examined the majority (861bp) of the coding region of the melanocortin-1 receptor (MC1R), a candidate gene for plumage color differentiation in 98 magpies from across the Australian continent, to determine if the gene is associated with magpie back-color variation and explore phylogeographic signal within the gene. Neutrality and selection tests (Tajima's D, Fu's F-S, MKT) indicate the gene is unlikely to be currently under selection pressure and, together with other lines of evidence, suggest a past demographic expansion event within the species congruent with the results of previous mitochondrial phylogeographic work on this species. None of the 15 synonymous and four nonsynonymous substitutions within MC1R were found to be associated with plumage variation. Our results suggest that genes or regulatory elements other than MC1R may determine back-color variation in C. tibicen.