Browsing by Author "Stephens, Kirstin"

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    Impacts of invasive birds: assessing the incidence and extent of hybridization between invasive Mallard Ducks (Anas platyrhynchos) and native Yellow-billed Ducks (Anas undulata) in South Africa
    (Stellenbosch : Stellenbosch University, 2019-03) Stephens, Kirstin; Le Roux, Johannes J.; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Hybridization with invasive species is a major impact on native congeners, often leading to introgression and the loss of unique genotypes or co-adapted gene complexes. Therefore, hybridization needs to be managed through the removal of invasive species and their hybrids. Such management is often hampered, due to difficulties in identifying hybrids without genetic information, as hybrids are often morphologically indistinguishable from parental species. Consequently, genetic monitoring has become a useful tool in the detection and management of hybridization. Public opposition is often an additional barrier to the control of charismatic invasive species. In the case of the invasive Mallard Duck (Anas platyrhynchos) in South Africa, there is strong public opposition to their removal, founded in part, upon a lack of awareness of the potential threat that Mallard Ducks pose to the native Yellow-billed Duck (A. undulata) through hybridization and subsequent introgression. Despite this threat, hybridization between the two species is still based on observational evidence with no scientific evidence to support the occurrence and extent of hybridization between these two species. With this thesis I aim to provide baseline genetic data for the Yellow-billed Duck in South Africa, and use population genetic analyses to determine if there is population genetic structure and differences in genetic diversity measures between widespread native populations. I also aim to determine if hybridization and introgression has occurred and whether sex-biased mating between Mallard and Yellow-billed Ducks occurs in South Africa. I used nuclear microsatellite DNA markers to determine genetic diversity measures and structure of Yellow-billed Ducks across three populations and historical museum samples from South Africa. The current populations represent a panmictic population with sufficient migration between them to prevent the formation of a strong population genetic structure. This has two implications: firstly, resources do not need to be focused on the conservation of genetically unique populations in South Africa and secondly, that there is the potential for hybridization to spread through long-distance migration between populations. Genetic diversity and structure have not changed significantly over time suggesting that there have been no major changes in the population numbers of Yellow-billed Ducks and their genetic diversity, up until now, is not negatively affected by anthropogenic threats such as urbanisation. To determine whether hybridization between Mallard and Yellow-billed Ducks, and introgression, have occurred in South Africa I used microsatellite genotype data to identify hybrid individuals and assign them to hybrid genotype classes. There is genetic evidence of hybridization and introgression between Mallard and Yellow-billed Ducks but most backcrossing and introgression is occurring into the Mallard Duck population. This means that the Yellow-billed Duck population is currently largely unaffected by introgression, but that it may become more extensive in the future. I also used DNA sequencing of a mitochondrial gene region to determine if there was sex-biased mating occurring between these two duck species. This approach revealed that most mating is occurring between Mallard Duck hens and Yellowbilled Duck drakes. These findings indicate that Mallard Duck hens should be prioritised for removal and that it is advisable to remove Mallard Ducks while there is still a chance of protecting the genetic integrity of the Yellow-billed Duck. These findings have implications for managing hybridization between the two species such as the prioritisation of the removal of Mallard Duck hens and that removal of Mallard Ducks has a good chance of protecting the genetic integrity of the Yellow-billed Duck. Moreover, if these findings are communicated to the public, it may convince them in favour of the removal of invasive Mallard Ducks.