Sequence Polymorphism in Candidate Genes for Differences in Winter Plumage between Scottish and Scandinavian Willow Grouse (Lagopus lagopus)

Background Population variation in the degree of seasonal polymorphism is rare in birds, and the genetic basis of this phenomenon remains largely undescribed. Both sexes of Scandinavian and Scottish Willow grouse ( Lagopus lagopus ) display marked differences in their winter phenotypes, with Scottish grouse retaining a pigmented plumage year-round and Scandinavian Willow grouse molting to a white morph during winter. A widely studied pathway implicated in vertebrate pigmentation is the melanin system, for which functional variation has been characterised in many taxa. Methodology/Principal Findings We sequenced coding regions from four genes involved in melanin pigmentation ( DCT , MC1R , TYR and TYRP1 ), and an additional control involved in the melanocortin pathway ( AGRP ), to investigate the genetic basis of winter plumage in Lagopus . Despite the well documented role of the melanin system in animal coloration, we found no plumage-associated polymorphism or evidence for selection in a total of ∼2.6 kb analysed sequence. Conclusions/Significance Our results indicate that the genetic basis of alternating between pigmented and unpigmented seasonal phenotypes is more likely explained by regulatory changes controlling the expression of these or other loci in the physiological pathway leading to pigmentation.