Browsing by Author "O'Ryan, C"

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    Initial assessment of triplex PCR assay application for detection of toxic dinoflagellates, Alexandrium species (Dinophyceae), in environmental samples
    (2004) Van Helmond, Z; O'Ryan, C; Sebastián, C Ruiz
    The frequency and geographical range of hannful algal blooms (HABs) are believed to be on the increase, with adverse affects on marine and human health making the implementation of stringent controls governmg monitoring programmes commonplace. The South African monitoring programme was established in 1989 and relies upon microscopic identification of HAB species. Microscopic identification is labour-intensive, requiring a high level of taxonomic expertise, and could be considered impractical for routine monitoring where analysis of large numbers of samples is required. Novel monitoring techniques, focusing mainly on probe technology, are being developed for rapid, unequivocal identification and enumeration of HAB species. In this study, a triplex peR assay, incorporating a genus-specific ribosomal DNA primer designed from phylogenetic studies on local Alexandrium populations, was optimised for application to environmental samples and tested against natural assemblages containing Alexandrium minutum. Specific positive results were consistently generated for samples containing A. minutum. Samples absent of A. minuturn cells did not generate the Alexandrium-specific amplicon. The absolute detection limit of 440 A. minutum cells r1 for this assay was established. Effects of non-target cells on the sensitivity of the assay were also investigated: although a decrease in sensitivity was found, A. minutum cells could still be detected in the presence of 100 times more non-target cells. This assay has been shown to be a useful tool for unequivocal identification of A. minutum cells within local environmental samples.
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    Population genetic structuring in the common mole-rat, Cryptomys hottentotus hottentotus
    (2002) Bishop, Jacqueline M; Jarvis, J U M; O'Ryan, C
    This thesis addresses the population genetic consequences of divergent social structure and dispersal regimes in two study populations of the common mole-rat Cryptomys hottentotus hottentotus. Aspects relating to the relationship between, gene flow and genetic variation, the roles of mutation and drift in promoting genetic structuring, and the role of genetic parentage in the species' mating system were investigated using a suite of cryptomys-specific microsatellite markers. C. h. hottentotus is a social species living in colonies of 2-14 individuals, permanently inhabiting a network of burrows. The species is a co-operative whose colonies are composed of a breeding pair, their offspring and a number of potentially unrelated individuals. C. h. hottentotus is an obligate outbreeder whose offspring delay dispersal and the opportunities for independent reproduction until both social and ecological conditions are favourable. The species is widely distributed across South Africa from extreme arid regions where low rainfall restricts dispersal for much of the year, to highly mesic areas where dispersal is facilitated all year round. In response to varying ecological constraints on dispersal, the species displays differential degrees of social elaboration across its range. This appears to be in response to the high energetic costs of burrowing and the low probability of locating geophyte clumps in increasingly arid environments.