Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula)

The mottled duck (Anas fulvigula) is a year-round endemicresident of the Gulf Coast and one of two non-migratory dabbling ducksthat inhabit North America. To investigate population genetic structureof allopatric mottled duck populations, we collected 5' control regionsequences (bp 78–774) from the mitochondria of 219 mottled duckssampled at 11 widely spaced geographic localities in Texas, Louisiana,and Florida and compared them to each other and to homologous sequencesfrom 4 Mexican ducks (A. diazi), 13 American black ducks(A. rubripes), and 10 mallards (A. platyrhynchos). Weidentified 57 unique haplotypes composed of 665 or 666 nucleotides inthe 246 control region sequences. Of the 665 homologous positions,8.3% (n = 55) vary among haplotypes, and98.2% (n = 54) of these occur within the first351 nucleotides from the 5' end of the outgroup sequence.Neighbor-joining analysis shows a large distal clade (52.5% ofmottled ducks sampled in our study) composed of two reciprocallymonophyletic clades of mottled duck haplotypes, one of which is endemicto Texas and Louisiana and the other endemic to Florida. No mottledducks sampled in Florida occur in the clade composed of mottled ducksfrom Texas and Louisiana or vice versa, suggesting that (1) an enduringgeographic split has existed for many years between east and west, and(2) gene flow currently is non-existent (or at least undetectable)across the central Gulf Coast. The remaining 47.5% of mottledducks sampled in our study branch basally from this derived clade, showsubstantially less hierarchical structure, and fall into various lineagegroups of mixed species composition with no geographic orspecies-specific pattern. Pairwise FST valuescorroborate the pattern of strong differentiation observed betweenTexas/Louisiana and Florida. Our findings are consistent with apattern of partial lineage sorting from a polymorphic ancestral genepool reshuffled by hybridizing mallards. Control region data andpatterns of divergence in mallard-like species worldwide, furthermore,suggest that mottled ducks are close relatives of Mexican ducks, and inturn nested within black ducks. Genetic similarities to nominatemallards are less likely to be the product of common ancestry, but theresult of past hybridization with a dichromatic mallard ancestor thatinvaded North America from Asia many generations ago. Our findings haveseveral important consequences for the conservation biology of mottledducks across the Gulf Coast and our understanding of the phylogeographyof mallard-like species worldwide.