Assessing the genetic impact of massive restocking on wild mallard

Abstract

Captive‐bred mallards Anas platyrhynchos have been released for hunting purposes at a very large scale in Europe since the mid‐1970s. In spite of a potential genetic impact, the actual contribution of restocked mallards to the genome of the target population has received little attention. The genetic structure of modern wild mallards in the Camargue, Southern France, was assessed from two samples: one originating from shot birds in hunting bags and one from presumed wild ducks captured alive in a hunting‐free reserve. Reference samples originated from five mallard farms, as well as from museum samples collected before the mid‐1970s (i.e. before massive mallard releases started). Our results revealed that the genetic signature of wild wintering mallards has not changed significantly because museum and presumed wild samples from the Camargue hunting‐free nature reserve were genetically similar, and clearly differentiated from the farm mallards. This suggests that mallard releases in the Camargue or elsewhere in France, although massive, have not actually translated into complete admixture of wild and captive genomes, most likely due to low survival of released birds once in the wild. Nevertheless, although genetic introgression of the wild population by captive‐bred was contained, we found significant rates of hybridization between wild and captive‐bred mallards in modern samples. This result suggests that long‐term releases of captive‐bred mallards, if carried on at such large scale, could compromise irreversibly the genetic structure and composition of European mallards. This work contributes to fill in the gap on the monitoring of the genetic consequences of large‐scale game releases for exploitation.

Admixture between released and wild game birds: a changing genetic landscape in European mallards (Anas platyrhynchos)

“…Indeed, most SNPs used in this study have rather intermediate allele frequencies (Kraus et al 2011a), and comparisons with other marker sets are not straightforward. This could explain the inconsistent results regarding heterozygosity between the current study and those by Champagnon et al (2013a) and Čížková et al (2012), who found a greater difference between farmed and wild mallards based on microsatellite analyses. Even though it is commonly acknowledged that the intrapopulation genetic structure of migratory birds is largely protected by philopatric habits (Liu et al 2012) or other migratory traditions (Jonker et al 2013), there are also examples of species with no signs of genetic structure on the continental scale (Reudink et al 2011).…”

“…Due to founder effects, inbreeding, and genetic drift, a differentiation between wild and farmed mallards could be expected. However, studies thus far on genetic differentiation give ambiguous results; Baratti et al (2009) did not find any differences using microsatellite markers, while Champagnon et al (2013a), Čížková et al (2012), and Baratti et al (2014) detected genetic differences between regional wild and farmed populations in France, Czech Republic, and Italy, respectively. Thus, more studies of genetic structure across multiple flyways are needed to assess the degree of differentiation and potential genetic homogenization at a larger spatial scale, using a common and more powerful methodological framework.…”

“…All samples from France as well as present-day samples from the Czech Republic had been used in precedent genetic studies. For further sample information and sampling protocols, see Table S1, Champagnon et al (2013a) and Čížková et al (2012).…”

“…Annual large-scale releases of farmed mallards are now a common practice in several European countries to increase the harvestable population . From a modest start in the 1970s, more than three million unfledged ducklings are currently released in the European Union for hunting purposes each year (Champagnon 2011), while the breeding population in the same area is 4.5 million pairs (Wetlands International 2015). In France alone, 1.4 million ducklings are released annually (Mondain-Monval and Girard 2000), to be compared to an estimated national winter population of 300,000 birds (Deceuninck et al 2014).…”

Crossing species boundaries : the hybrid histories of the true geese

“…In addition, huge numbers of farm-reared Mallards are interbreeding with their wild conspecifics. The low genetic diversity of the captive birds threatens the genetic integrity of the wild populations in Sweden, France and the Czech Republic (Cizkova et al, 2012, Champagnon et al, 2013. A well-known case of waterfowl hybridization involves the Ruddy Duck (Oxyura jamaicensis) which was introduced to the UK in the 1950s and spread to Spain where it hybridized with the endangered White-headed Duck (Oxyura leucocephala).…”