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

Abstract

The mottled duck (Anas fulvigula) is a year-round endemic resident of the Gulf Coast and one of two non-migratory dabbling ducks that inhabit North America. To investigate population genetic structure of allopatric mottled duck populations, we collected 5’ control region sequences (bp 78–774) from the mitochondria of 219 mottled ducks sampled at 11 widely spaced geographic localities in Texas, Louisiana, and Florida and compared them to each other and to homologous sequences from 4 Mexican ducks (A. diazi), 13 American black ducks (A. rubripes), and 10 mallards (A. platyrhynchos). We identified 57 unique haplotypes composed of 665 or 666 nucleotides in the 246 control region sequences. Of the 665 homologous positions, 8.3% (n = 55) vary among haplotypes, and 98.2% (n = 54) of these occur within the first 351 nucleotides from the 5’ end of the outgroup sequence. Neighbor-joining analysis shows a large distal clade (52.5% of mottled ducks sampled in our study) composed of two reciprocally monophyletic clades of mottled duck haplotypes, one of which is endemic to Texas and Louisiana and the other endemic to Florida. No mottled ducks sampled in Florida occur in the clade composed of mottled ducks from Texas and Louisiana or vice versa, suggesting that (1) an enduring geographic 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 mottled ducks sampled in our study branch basally from this derived clade, show substantially less hierarchical structure, and fall into various lineage groups of mixed species composition with no geographic or species-specific pattern. Pairwise FST values corroborate the pattern of strong differentiation observed between Texas/Louisiana and Florida. Our findings are consistent with a pattern of partial lineage sorting from a polymorphic ancestral gene pool reshuffled by hybridizing mallards. Control region data and patterns of divergence in mallard-like species worldwide, furthermore, suggest that mottled ducks are close relatives of Mexican ducks, and in turn nested within black ducks. Genetic similarities to nominate mallards are less likely to be the product of common ancestry, but the result of past hybridization with a dichromatic mallard ancestor that invaded North America from Asia many generations ago. Our findings have several important consequences for the conservation biology of mottled ducks across the Gulf Coast and our understanding of the phylogeography of mallard-like species worldwide.