Evolution and connectivity in the world-wide migration system of the mallard: Inferences from mitochondrial DNA

Abstract

BackgroundMain waterfowl migration systems are well understood through ringing activities. However, in mallards (Anas platyrhynchos) ringing studies suggest deviations from general migratory trends and traditions in waterfowl. Furthermore, surprisingly little is known about the population genetic structure of mallards, and studying it may yield insight into the spread of diseases such as Avian Influenza, and in management and conservation of wetlands. The study of evolution of genetic diversity and subsequent partitioning thereof during the last glaciation adds to ongoing discussions on the general evolution of waterfowl populations and flyway evolution. Hypothesised mallard flyways are tested explicitly by analysing mitochondrial mallard DNA from the whole northern hemisphere.ResultsPhylogenetic analyses confirm two mitochondrial mallard clades. Genetic differentiation within Eurasia and North-America is low, on a continental scale, but large differences occur between these two land masses (FST = 0.51). Half the genetic variance lies within sampling locations, and a negligible portion between currently recognised waterfowl flyways, within Eurasia and North-America. Analysis of molecular variance (AMOVA) at continent scale, incorporating sampling localities as smallest units, also shows the absence of population structure on the flyway level. Finally, demographic modelling by coalescence simulation proposes a split between Eurasia and North-America 43,000 to 74,000 years ago and strong population growth (~100fold) since then and little migration (not statistically different from zero).ConclusionsBased on this first complete assessment of the mallard's world-wide population genetic structure we confirm that no more than two mtDNA clades exist. Clade A is characteristic for Eurasia, and clade B for North-America although some representatives of clade A are also found in North-America. We explain this pattern by evaluating competing hypotheses and conclude that a complex mix of historical, recent and anthropogenic factors shaped the current mallard populations. We refute population classification based on flyways proposed by ornithologists and managers, because they seem to have little biological meaning. Our results have implications for wetland management and conservation, with special regard to the release of farmed mallards for hunting, as well as for the possible transmission of Avian Influenza by mallards due to migration.

Flexibility of Continental Navigation and Migration in European Mallards

“…This explanation would not allow us to make conclusions about the navigational abilities of the birds, as we don’t know where the birds came from. However, these cases are not distinguishable from the data available, and since populations all over Eurasia resemble each other to a high extent, discrimination by genetic means would not be possible [36]. Overall, we observed a great amount of flexibility in mallards, in both their navigation strategies and their decisions to migrate in both winter and spring.…”

Extensive Allelic Diversity of MHC Class I in Wild Mallard Ducks

“…This could be established by examining mitochondrial DNA (mtDNA). Analyses of mtDNA of mallards sampled worldwide indicate that Eurasian ducks possess mtDNA haplotype A, whereas North American ducks are predominantly haplotype B (including other native species) with a few haplotype A sequences suggesting significant gene flow has occurred into North America (64,65). Although duck populations are undoubtedly influenced by many factors, including migration, farming, and release of captive birds, the likely source of the introgression of European genes is through recent or historical admixture as ducks currently intermingle in the Aleutian Islands, and historical colonization of the North American landmass likely took place through the Beringia land bridge.…”

The Evolution of Innate Immune Genes: Purifying and Balancing Selection on β-Defensins in Waterfowl

“…DNA was extracted from wild-caught mallards and both captive and wild-caught Anatidae species via ammonium acetate precipitation, or as described in Kraus et al (2011). The mallard genome (Huang et al 2013) was searched to locate b-defensin genes, based on the conserved six cysteine motif C X 4-8 C X 3-5 C X 9-13 C X 4-7 CC, where X can be any amino acid.…”

“…Among sampled individuals, 11 (4%) were captured in both years, genotyped and scored independently to ensure repeatability of allele assignments. For global mallards, samples were collected as described in Kraus et al (2011;2013 …”