Mallard (1 Viewer)

Abstract
Waterbirds are currently facing various threats throughout the world. One threat that is often overlooked is hybridisation with introduced species. This threatening process is especially significant for dabbling ducks (Genus Anas). The Mallard (Anas platyrhynchos) has been introduced to various parts of the world and now hybridises and threaten numerous Anas species. In this paper, we review hybridisation between Mallards and dabbling ducks with a specific emphasis on threats to the Pacific Black Duck (A. superciliosa). We then present an overview of the potential mechanisms of hybridisation and discuss monitoring techniques. We conclude by proposing management strategies and speculating on the future of native dabbling duck species.

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Abstract
Quantifying the genetic composition of founder populations is important to the success of reintroduction programs, especially for bottlenecked and/or specialized species, such as island endemics. By implementing admixture schemes based on genetic variability, captive breeding programs can minimize the detrimental effects of bottlenecking, inbreeding depression, outbreeding depression, etc. Particular attention has been given to genes within the major histocompatibility complex (MHC) due to their direct correlation to an individual's immunity. However, isolating and amplifying MHC haplotypes remains difficult owing to the high diversity and paralogous nature. We describe a method of MHC I haplotype isolation based on an iterative process of primer design for the endangered island endemic, the Laysan duck (Anas laysanensis). Ultimately, haplotype-specific primers allow for direct genotyping after gel electrophoresis based on the presence/absence of their respective amplicons. Using the developed techniques, a total of eight unique haplotypes were isolated and assayed across 21 Laysan duck individuals from Laysan Island (N = 10) and Midway Island (N = 11). The presence/absence of seven haplotypes were variable across individuals with three haplotypes present in 95% of individuals, three in 38% of individuals, and one in 90% of individuals. The protocols described herein provide a simple, cost-effective method for isolating haplotypes and monitoring existing MHC variation in Laysan ducks, and the general approach can be applied to other molecular markers and species with low genetic diversity.

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Speciation is regarded primarily as a bifurcation from an ancestral species resulting in two distinct taxonomic units. Although hybrid speciation is known to occur, such events have been regarded as rare in homoploid systems. Here, we provide several lines of evidence supporting the hypothesis that the endangered Hawaiian duck (Anas wyvilliana) is descended from ancient hybridization between the mallard (A. platyrhynchos) and Laysan duck (A. laysanensis). Specifically, using coalescent methods, we reveal that gene flow from either of the putative parental species is necessary to explain the diversity and apparent genomic mosaic within the Hawaiian duck. We discuss how island systems might act as arenas for interspecific hybridization leading to speciation as a result of rapid isolation between hybrids and parental species. Hybrid speciation may be a more common mechanism than previously thought for generating biodiversity, especially during rapid radiations.

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Richard Klim said:

Forthcoming...

Guay, Taysom, Robinson & Tracey (in press). Hybridisation between the Mallard and native dabbling ducks: causes, consequences and management. Pac Conserv Biol.

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Richard Klim said:

Guay, Taysom, Robinson & Tracey (in press). Hybridisation between the Mallard and native dabbling ducks: causes, consequences and management. Pac Conserv Biol.

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Peter Kovalik said:

Grallards: New Zealand's next extinction or newest species?

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The threat of hybridisation with Mallards (Anas platyrhynchos) posed to many dabbling duck species is one that is commonly overlooked. Introduced Mallards have interbred with the Pacific Black Duck (A. superciliosa), to the extent that the New Zealand subspecies is now considered endangered. In Australia, introduced Mallards are typically of domestic origin and were originally believed to be restricted to urban areas. The degree of hybridisation between Mallard and the Pacific Black Duck is currently unknown, largely because hybrid backcrosses are difficult to visually identify. A technique using microsatellite markers was established to genetically identify hybrids. This system utilises 9 markers that were tested on putatively pure Pacific Black Ducks and domestic Mallards. Assignment tests, performed with the program Structure, had a 99% likelihood that specimens of a known species (Mallard or Black Duck) were assigned to the correct group. The marker set established was used to test the rate of hybridisation throughout Australia. Assignment tests were performed, as previous, on 372 specimens from 6 different Australian states. Overall, the proportion of hybridisation was less than 0.01, however, an increased rate was found in the states of Tasmania and Western Australia (0.03 and 0.16 respectively). This result suggests that hybrids are not common, but are increasing in the areas of Tasmania and Western Australia. Furthermore, all samples from Western Australia were collected from urban areas, whereas all other samples were from rural regions. An increased rate of hybridisation in Western Australia compared to other states supports theory that hybrids may be more prevalent in urban areas where Mallards are more common. More study of hybridisation in urban areas is required to determine whether urban ponds act as reservoirs for Mallard genes and whether these reservoirs may be a threat to the genetic integrity of the Australian Pacific Black Duck.

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Richard Klim said:

Lavretsky, Hernández-Baños & Peters 2014. Rapid radiation and hybridization contribute to weak differentiation and hinder phylogenetic inferences in the New World Mallard complex (Anas spp.). Auk 131(4): 524–538. [abstract]

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Richard Klim said:

Lavretsky, Engilis, Eadie & Peters. Islands as venues for homoploid hybrid speciation: A case for the endangered hawaiian duck. Evolution 2014. (p288)

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