Hybridization and Population Structure of Western Gulf Coast Mottled Ducks

Abstract

Rates of hybridization between species that do not normally interbreed have increased due to human impacts on natural environments, such as habitat alteration or introductions of non-native species. Human-induced hybridization can be detrimental to wildlife and contribute to species extinctions. In Florida, feral Mallards (Anas platyrhynchos) hybridize with endemic Mottled Ducks (A. fulvigula) at rates close to 9%. However, levels of hybridization between these two species have not been extensively examined in the western Gulf Coast (from Alabama to northern Mexico) despite the potential impact on the Mottled Duck lineage. In this study, I examined the degree of hybridization between Mottled Ducks and Mallards in the western Gulf Coast. In addition, I validated a key developed in Florida to distinguish Mottled Ducks from Mallards and their hybrids for western Gulf Coast Mottled Ducks. Lastly, I examined the genetic structure of Mottled Duck populations and estimated gene flow by determining the number of migrants between regions across the western Gulf Coast. I used 36 microsatellite loci to genotype 405 ducks including putative Mottled Ducks, Mallards, and hybrids. Overall, genetic analyses revealed very low rates of hybridization (5.4%) in the western Gulf Coast. The key to distinguish Florida Mottled Ducks from Mallards and their hybrids proved highly effective (97%) for the western Gulf Coast population. Finally, multiple analyses indicated that Mottled Ducks are a single genetic population across the western Gulf Coast, which may be primarily due to dispersal of juvenile ducks. Currently, hybridization with Mallards is not a threat to western Gulf Coast Mottled Ducks; however, Mottled Duck hybridization should be monitored in the future to ensure that hybridization rates do not increase.