Differences in the growth rate and immune strategies of farmed and wild mallard populations

Abstract

Individuals reared in captivity are exposed to distinct selection pressures and evolutionary processes causing genetic and phenotypic divergence from wild populations. Consequently, restocking with farmed individuals may represent a considerable risk for the fitness of freeliving populations. Supportive breeding on a massive scale has been established in many European countries to increase hunting opportunities for the most common duck species, the mallard (Anas platyrhynchos). It has previously been shown that mallards from breeding facilities differ genetically from wild populations and there is some indication of morphological differences. Using a common-garden experiment, we tested for differences in growth parameters between free-living populations and individuals from breeding facilities during the first 20 days of post-hatching development, a critical phase for survival in free-living populations. In addition, we compared their immune function by assessing two haematological parameters, H/L ratio and immature erythrocyte frequency, and plasma complement activity. Our data show that farmed ducklings exhibit larger morphological parameters, a higher growth rates, and higher complement activity. In haematological parameters, we observed high dynamic changes in duckling ontogeny in relation to their morphological parameters. In conclusion, our data demonstrate pronounced phenotype divergence between farmed and wild mallard populations that can be genetically determined. We argue that this divergence can directly or indirectly affect fitness of farmed individuals introduced to the breeding population as well as fitness of farmed x wild hybrids.

Population Genetics of a Translocated Population of Mottled Ducks and Allies

“…Despite a relatively low rate of hybridization (i.e.,~10%; n = 4) between mottled ducks and game-farm mallards in South Carolina, our evidence suggests that some proportion of these game-farm mallards indeed survive outside their release site and interbreed with local congeners (Lavretsky et al 2019(Lavretsky et al , 2020. Being under artificial selection for desired domestic traits (e.g., breeding propensity), all domestic mallards differ in fertility, overall morphology, and biology from their wild counterparts (Miller 1977, Paulke and Haase 1978, Söderquist et al 2013, Svobodová et al 2020). The movement of their genetic variation and associated maladaptive traits into wild populations may reduce survival and fecundity of wild mottled ducks (Söderquist et al 2014, McFarlane and Pemberton 2019, Svobodová et al 2020, Söderquist et al 2021.…”

“…Being under artificial selection for desired domestic traits (e.g., breeding propensity), all domestic mallards differ in fertility, overall morphology, and biology from their wild counterparts (Miller 1977, Paulke and Haase 1978, Söderquist et al 2013, Svobodová et al 2020). The movement of their genetic variation and associated maladaptive traits into wild populations may reduce survival and fecundity of wild mottled ducks (Söderquist et al 2014, McFarlane and Pemberton 2019, Svobodová et al 2020, Söderquist et al 2021. Feral mallards now pose a genetic threat to global populations of wild mallard and mallard-like taxa, with confirmed feral × wild hybrid swarms in Eurasia (Söderquist et al 2014(Söderquist et al , 2017, mainland North America (Lavretsky et al 2019(Lavretsky et al , 2020, and Hawaii (Wells et al 2019), all of which show declining populations.…”

Sex-Specific Life History Affected by Stocking in Juvenile Brown Trout

“…Despite this, intersexual differences in early life history strategies receive little attention when studying the fitness of individuals and/or assessing population viability (Tarka et al, 2018). Stock enhancement practices primarily focus on the release of early life stages but sex effects are only rarely considered [but see for example Huertas and Cerdà (2006), Lenz et al (2007), and Svobodová et al (2020)]. Sex-specific early life history strategies, and their relationship with stock enhancement practices, may thus be a hidden driver of population dynamics and need to be studied in more detail.…”

Differential gene expression reveals host factors for viral shedding variation in mallards (Anas platyrhynchos) infected with low-pathogenic avian influenza virus

“…Wild-bred mallards collected in ovo were used for this study. Analysing the gene expression of wild birds is important due to the inherent genetic variation within the population [56], a probable factor driving variation in a species response to viral infection [16]. Eggs were collected from hen nests located in uncultivated fields of Towner County, North Dakota, USA (48.44, –99.31) in May– June 2015, and shipped to MSU where they were incubated (Sportsman 1502 Egg Incubator; GQF Manufacturing) at 37.5 °C with 45–50 % humidity until hatched.…”