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J.1-1: Population Genetics and Hybridization of Mallards and Mallard-Like Ducks in North America

Presented by Philip Lavretsky - Email: plavretsky@utep.edu

North America is home to five recently diverged, New World “mallards,” a group of dabbling duck species characterized by diagnosable phenotypic differences but minimal genetic differentiation. I present genomic data used to characterize population structure within this group, estimate gene flow, as well as identify signatures of selection across their genomes. In contrast to previous studies, coupling landscape-level sampling efforts and the thousands of genetic markers assayed using ddRAD sequencing methods successfully assigned individuals to their respective taxon or hybrid class. First, I find limited evidence of contemporary gene flow between the dichromatic mallard and several monochromatic taxa, but find evidence for ancient gene flow between some monochromatic species pairs. Additional analyses focusing on mallards and American black ducks further supported that these two have always been closely related, and that American black ducks are not on their path to becoming a “hybrid swarm.” Thus, despite recurring cases of hybridization in this group, I conclude that the overall genetic similarity of these taxa likely reflects retained ancestral polymorphism rather than recent and extensive gene flow. In fact, I report previously unknown outlier regions across the Z-chromosome and several autosomal chromosomes that may have been involved in the diversification of the New World Mallard clade. These results challenge the current dogma predicting the genetic extinction of the New World monochromatic dabbling ducks via introgressive hybridization with mallards. Conversely, I provide evidence from century-old (1842-1915) and contemporary (>2009) mallard comparisons that confirm that the intensive stocking practices of game-farm mallards conducted across the last century has fundamentally changed the genetic integrity of North America’s wild mallard population, especially in eastern North America. It becomes of great interest to ask whether the iconic North American mallard is declining in the wild due to introgression of maladaptive traits from domesticated forms.
Session: Eastern Mallards & Brown Ducks (Friday, August 30,13:20 to 15:00)