A morphological and genetic investigation of the highest-latitude endemic passerine: McKay's bunting

Abstract

I used two different approaches to investigate different aspects of the highest latitude endemic passerine, McKay's Bunting (Plectrophenax hyperboreus). I tested whether or not the juvenal plumage of McKay' s Bunting is different from its closest relative, Snow Bunting (P. nivalis). Using light reflectance spectrophotometry to quantify visual differences, I found that McKay's and Snow buntings have significantly different juvenal plumages. This analysis supports their separation into two distinct species. Second, I investigated the genetic consequences of refugial isolation and the model of speciation that the genetic data fit. This species pair provides an excellent opportunity to investigate the genetic effects of speciation at high latitudes in a region known to be significantly impacted by Pleistocene climatic oscillations. Using a mitochondrial marker and anonymous nuclear markers, I found evidence for recent divergence and a very small founding population size of McKay's. After the founder event, there is evidence of a population expansion and a subsequent reduction of the McKay's population, probably as a result of rising sea levels and asymmetric hybridization into Snow Buntings postglacially colonizing Beringia. This recent, high latitude speciation event fits a model of founder effect peripatric speciation driven by a small founding population size and genetic drift.