Michael L. Schummer , John Simpson, Brendan Shirkey, Samuel R. Kucia, Philip Lavretsky, Douglas C. Tozer
Fig 1. Waterfowl survey areas currently assigned to the eastern and mid-continent stocks of mallards as identified by the United States Fish and Wildlife Service (USFWS) for management purposes.
- Published: March 15, 2023 https://doi.org/10.1371/journal.pone.0282874
Abstract
The genetic composition of mallards in eastern North America has been changed by release of domestically-raised, game-farm mallards to supplement wild populations for hunting. We sampled 296 hatch-year mallards harvested in northwestern Ohio, October–December 2019. The aim was to determine their genetic ancestry and geographic origin to understand the geographic extent of game-farm mallard introgression into wild populations in more westward regions of North America. We used molecular analysis to detect that 35% of samples were pure wild mallard, 12% were early generation hybrids between wild and game-farm mallards (i.e., F1–F3), and the remaining 53% of samples were assigned as part of a hybrid swarm. Percentage of individuals in our study with some form of hybridization with game-farm mallard (65%) was greater than previously detected farther south in the mid-continent (~4%), but less than the Atlantic coast of North America (~ 92%). Stable isotope analysis using δ2Hf suggested that pure wild mallards originated from areas farther north and west than hybrid mallards. More specifically, 17% of all Ohio samples had δ2Hf consistent with more western origins in the prairies, parkland, or boreal regions of the mid-continent of North America, with 55%, 35%, and 10% of these being genetically wild, hybrid swarm, and F3, respectively. We conclude that continued game-farm introgression into wild mallards is not isolated to the eastern population of mallards in North America, and may be increasing and more widespread than previously detected. Mallards in our study had greater incidence of game-farm hybridization than other locales in the mid-continent but less than eastern North American regions suggesting further need to understand game-farm mallard genetic variation and movement across the continent.
Fig 2.
Population structure analyses based on 22,136 independent bi-allelic ddRAD-seq SNPs assayed across Ohio (OH) samples, as well as reference wild (WMA) and game-farm (GFM) mallards, including (A) a plot of the first two principal components of the principal components analysis (PCA) and (B) ADMIXTURE assignment probabilities attained under an optimum K populations of 2 (S2B Fig). Finally, we provide the (C) expected average and range of assignment probabilities across simulated generations (left), as well as the proportion of Ohio samples falling into those generations (right).
Introduction
Humans and mallards (Anas platyrhynchos) have a closely linked history since their domestication in China around 500 B.C. [1, 2]. Nearly all domestic ducks (e.g., Pekin duck) are decedents of wild, Eurasian mallards [1]. The intentional supplementation of wild populations is common practice for many game species [3–6] including waterfowl [7, 8]. Although wild mallard populations naturally have a Holartic distribution, the intentional introduction of wild and domesticated forms has artificially increased their distribution to nearly everywhere but the Poles [9]. Among domestic mallards, the intentional release of the game-farm mallard breed is responsible for the majority of their range expansion. Started in the early 20th century, the release of game-farm mallards continues intensively today in Europe (6-million annually) [10, 11] and eastern North America (≥ 200,000 annually) [12–14] largely for the supplementation of wild mallard populations for hunting purposes [14, 15]. Much like other domesticated mallard forms, all game-farm mallards have a Eurasian origin, and those being released in Europe and North America are from the same genetic source [10–12]. Introduction of game-farm mallards were thought to have no impact on wild populations, but only recently have molecular studies begun to estimate levels of introgression of game-farm genes into wild mallard populations. Wild mallards are genetically panmictic [16], but release of game-farm mallards has changed the genetic ancestry of wild populations in Europe [17] and North America [18, 19]. Increasing prevalence of game-farm genes within wild populations is predicted to decrease mallard fitness because of introduction of artificially selected, maladaptive traits [17, 19], and this has been hypothesized to at least partially explain recent mallard population declines in eastern North America [19] and central Europe [17].
Open Access PLOS article in PDF or HTML format
I Really Appreciate Science 