title: Wild mallards have more "goose-like" bills than their ancestors: a case of anthropogenic influence?
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.
authors.affiliation: Division of Natural Sciences, Kristianstad University, SE-291 88 Kristianstad, Sweden; Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, SE-901 83, Umeå, Sweden.
authors.forename: Pär
authors.initials: P
authors.lastname: Söderquist
authors.affiliation: Division of Natural Sciences, Kristianstad University, SE-291 88 Kristianstad, Sweden.
authors.forename: Joanna
authors.initials: J
authors.lastname: Norrström
authors.affiliation: Division of Natural Sciences, Kristianstad University, SE-291 88 Kristianstad, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Elmberg
authors.affiliation: Office National de la Chasse et de la Faune Sauvage, CNERA Avifaune Migratrice, La Tour du Valat, Le Sambuc, 13200 Arles, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Guillemain
authors.affiliation: Division of Natural Sciences, Kristianstad University, SE-291 88 Kristianstad, Sweden.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Gunnarsson
mesh_terms: D000818:Animals; D001502:Beak / Q000033:anatomy & histology*; D001837:Body Weights and Measures; D001947:Breeding; D004372:Ducks / Q000033:anatomy & histology*; D005260:Female; D005387:Finland; D008297:Male; D009664:Norway; D013548:Sweden