Masters Degrees (Genetics)

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Browsing Masters Degrees (Genetics) by Subject "Abalone -- Breeding"

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    Microsatellite markers as a tool in genetic enhancement and husbandry of Haliotis midae : a South African case study
    (Stellenbosch : Stellenbosch University, 2012-03) Swart, Liana; Roodt-Wilding, R.; Slabbert, R.; Stellenbosch University. Faculty of AgriSciences. Dept. of Genetics.
    ENGLISH ABSTRACT: The decline of Haliotis midae (perlemoen) populations together with the ensuing collapse of commercial abalone fisheries in South Africa have shifted the responsibility to abalone farms to meet the demand for perlemoen. Attention has recently turned to the genetic enhancement of cultured abalone in order for the farms to remain competitive in the international aquaculture market. To develop a successful breeding programme it is imperative to draw on a good foundation of high levels of genetic diversity and to successfully maintain these levels in order to create an enhanced strain of cultured abalone. A Performance Recording Scheme (PRS) was established as the first breeding programme for Haliotis midae to utilise molecular tools. This programme was aimed at enhancing the growth rate of abalone in order to shorten the production times on farms. The current study made use of 12 species-specific microsatellite markers to assign parentage to a group of faster-growing PRS animals, as selected by the abalone farms, in order to select a diverse on-farm generation of broodstock. Additionally, the influence of standard selection practises on the genetic diversity of a population compared to genotypic selection was investigated. This data was also used to study the differentiation and levels of genetic diversities within and between cultured and wild populations. Selection based on genotypic traits successfully retained genetic diversity while some diversity was lost in phenotypically selected populations. These phenotypic populations differed significantly from each other and wild populations, while the genotypic populations were similar in genetic composition to each other and wild populations of the West coast. The broodstock populations used in the PRS spawning event were representative of the wild populations from where they were sourced, with no significant differentiation between the broodstock and West coast population. When these broodstock populations were compared to their corresponding offspring populations, only two populations displayed a significant loss in diversity; although all of the offspring populations showed significant differentiation with their corresponding broodstock populations. This was attributed to the differential contribution of broodstock and the effect of artificial selection. It was established that the cultured populations of the participating abalone farms should be used with caution in ranching and reseeding programmes. These populations differed significantly from both the East and West coast wild populations. This study concluded that it is possible to retain genetic diversity by selecting breeding animals based on genotypic traits. The loss of diversity in some cultured populations and significant differentiation from the wild populations indicate that animals are exposed to different selection pressures in the cultured environment. The results found in this study highlight the need for the effective management of hatchery practices and the genetic monitoring of the breeding animals.