Ecology and population genetics of mottled ducks within the south Atlantic coastal zone
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The mottled duck (Anas fulvigula maculosa) is a non-migratory waterfowl species native to Texas and Louisiana. The subspecies, A. f. fulvigula, is endemic to Florida. About 1,200 mottled ducks were introduced to the Santee River Delta and the ACE (Ashepoo, Combahee, and Edisto Rivers) Basin of South Carolina during 1975-82 from their native habitats for hunting opportunities. Impacts of translocation and establishment of mottled ducks on the introduced population per se, on other native species, and on ecosystem processes were not considered. I collected harvest data and survey data to evaluate the change in abundance and distribution of mottled ducks along the South Atlantic Coastal Zone (SACZ). Abundance of mottled ducks in South Carolina has increased since the end of the introduction. Distribution of mottled ducks expanded southward and two new breeding populations were established by the introduced birds in Savannah, South Carolina and Rhetts Island, Altamaha Wildlife Management Area (WMA) in Georgia. I studied factors affecting habitat use by mottled ducks at Bear Island WMA. Water depth, submerged vegetation, and aquatic invertebrates were measured at locations used and not used by mottled ducks. Water depth was the only factor associated with habitat use by mottled ducks and they seldom used water deeper than 25 cm. I used nine microsatellite DNA loci to analyze 807 mottled ducks collected from South Carolina, Georgia, Florida, Louisiana, and Texas. The genetic data showed a clear hierarchical population structure reflecting the geographic relationship of mottled ducks along the SACZ. The two subspecies of mottled ducks were separated in a cluster analysis using the genetic data except that mottled ducks from Guana River WMA in Florida were in the cluster of Texas-Louisiana subspecies. Gene flow from the introduced birds to native populations in Florida was revealed by the population structure, smaller genetic distance between Georgia and Florida populations than that among native populations, negative correlation between genetic and geographic distances, and private alleles found in Guana River population. Management practices for mottled ducks may seek to control this directional gene flow.