Abstract
Wild populations of the world’s most common dabbling duck, the mallard (Anas platyrhynchos), run the risk of genetic introgression by farmed conspecifics released for hunting purposes. We tested whether bill morphology of free-living birds has changed since large-scale releases of farmed mallards started. Three groups of mallards from Sweden, Norway and Finland were compared: historical wild (before large-scale releases started), present-day wild, and present-day farmed. Higher density of bill lamellae was observed in historical wild mallards (only males). Farmed mallards had wider bills than present-day and historical wild ones. Present-day wild and farmed mallards also had higher and shorter bills than historical wild mallards. Present-day mallards thus tend to have more “goose-like” bills (wider, higher, and shorter) than their ancestors. Our study suggests that surviving released mallards affect morphological traits in wild population by introgression. We discuss how such anthropogenic impact may lead to a maladapted and genetically compromised wild mallard population. Our study system has bearing on other taxa where large-scale releases of conspecifics with ‘alien genes’ may cause a cryptic invasive process that nevertheless has fitness consequences for individual birds.
Highlights
Anthropogenic impact is one of the biggest threats nature stands before today [1]
Post-hoc tests revealed that historical wild males had significantly higher lamellar density than farmed mallards (p50.020), historical wild mallards tended to have a higher lamellar density than present-day wild mallards for the same position (p50.051)
Champagnon et al [30] argued that farmed mallards might have lower lamellar density because they are fed with large food-pellets at the duck farms and the selection for denser lamellae has been relaxed for generations
Summary
Anthropogenic Change of Mallard Bill Morphology [2, 3]. Such exotics, when they become invasive, threaten native fauna through a variety of ways, e.g. competition for resources and predation [4], as well as genetic introgression when they interact with taxonomically close species [5]. Beyond possible effects at the level of ecological communities, there is growing concern about effects on the spatial genetic structure within species when conspecifics of non-local provenance are released to supplement populations, e.g. for conservation or harvest purposes [6]. A recent review shows that, for a wide range of taxa, reintroduction programs and supplemental stocking of native species need to consider the provenance of the individuals released so as not to introduce non-native genes [7]. Failure to do so may lead to a scenario of ‘cryptic invasion’ sensu [8]
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