The white neck-ring of the Eurasian Teal Anas crecca: rare mutation or stable morph? A first genetic and heuristic analysis

Capsule: Individual Eurasian Teal Anas crecca with white neck-rings have been found in Italy and an extensive museum survey found this plumage character occurring with a low frequency, although no genetic difference was observed with respect to the normal phenotype. Aims: To estimate the relative frequency and distribution of this plumage variation and to provide a first genetic assessment to verify if this character could have a taxonomic basis or if it occurs by chance among populations. Methods: An extensive museum survey was conducted to check for the occurrence of white neck-ringed Eurasian Teals in preserved specimens from its distributional range. A genetic analysis was conducted at standard mitochondrial loci (D-loop and COI) of ten white neck-ringed Eurasian Teals from Venice lagoon, Italy. Haplotypes were compared with genetic data from Holarctic populations. Results: The museum survey uncovered additional cases of white neck-ringed Eurasian Teals in Italy and Europe. Moreover, this mutation has also been documented for the first time in the North American Green-winged Teal Anas carolinensis. The white neck-ring was found to be variable in size and occurred in both sexes and in different age classes in about 1.5% of examined individuals. The genetic analysis did not show any significant lineage differentiation between them and the normal phenotype, but the Italian samples showed high values of haplotype diversity indicating a key role of northeast Italy in attracting different migratory populations in winter. Conclusions: While the same variation occurs in many other species of the tribe Anatini, none of these cases clearly suggested the occurrence of hybridization, progressive greying, environmental causation or another kind of locally frequent mutation. It is most likely this plumage trait is a form of leucism or the expression of an ancestral phenotype, possibly occurring in different populations within the species’ range