Browsing by Author "Diedericks, Genevieve"

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    Determining the mechanisms driving the invasion success of the smallmouth bass (Micropterus dolomieu, Lacepède 1802)
    (Stellenbosch : Stellenbosch University, 2017-12) Diedericks, Genevieve; Hui, Cang; Von der Heyden, Sophie; Weyl, Olaf L. F.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH Abstract: Biological invasions represent a significant threat to the Earth’s biota, including freshwater ecosystems. Whilst various studies have been conducted on invasive species in the hopes of establishing a set of general guidelines to facilitate our understanding of the invasion pathway and the features (organismal or environmental) that may assist in a species’ invasion success, predictions and generalisations remain challenging and limited. While general guidelines and unified frameworks are essential in furthering our understanding of biological invasions, exploring the genetic and phenotypic variation in a species and the influence of extrinsic factors during adaptation to novel environments could provide insight into a species’ invasion success. By utilising an array of methods, spanning different disciplines, this dissertation evaluates the potential mechanisms driving a species’ invasive success using the smallmouth bass, Micropterus dolomieu, as model organism. First, I attempt to unravel the role of genetic diversity in a species’ invasive success, by assessing the genetic differentiation and diversity within M. dolomieu populations in the invaded South African (SA) range, and examine how the genetic diversity may change over time in both native (USA) and invasive ranges (Chapter 2). By conducting a three-way comparison on two mitochondrial (mtDNA) and nine microsatellite loci for a total of 572 M. dolomieu specimens, representing the contemporary invasive SA range, contemporary native USA range and the historic native USA range (dating back to the period of introduction into SA), I reveal the presence of elevated levels of genetic diversity for the invasive SA range. The levels of genetic diversity for both the contemporary native and invasive ranges are, however, substantially lower than those of the historic native range, suggesting that both contemporary populations experienced a recent genetic bottleneck followed by a rapid population expansion. As admixture, and more specifically introgressive hybridisation, may contribute to these elevated levels of genetic diversity observed within the invaded SA range, I subsequently test the hypothesis that hybridisation and introgression can occur between two invasive species in a novel invaded range (Chapter 3). Using two notorious freshwater invaders (M. dolomieu and M. salmoides), I assess the level of introgressive hybridisation between the two species, using two mtDNA and nine microsatellite loci. Despite large uncorrected pairwise distances being observed between the two species, unidirectional mitochondrial introgression was detected, suggesting that introgressive hybridisation may play a pivotal role in the successful establishment and spread of alien invasive species upon introduction. The remaining chapters focus on the role of morphological variation in response to environmental variation in the novel invaded range. First, I test the hypothesis that environmental variation drives morphological changes in phenotype (Chapter 4). Analyses of linear and geometric morphometrics, as well as environmental variables, show a strong correlation between body depth and flow regime, with streamlined fish inhabiting high-flow environments. In addition, the presence of variation in gape size among localities suggests a link between cranial morphology and prey composition associated with substrate type. These results support the idea that similar environments have convergent phenotypes and highlight the importance of phenotypic plasticity in facilitating the successful colonisation, establishment and spread of invasive species. However, as gene flow may erase phenotypic variation associated with plasticity, I continue by exploring the genetic basis to local adaptation (Chapter 5). By combining linear morphometrics and genotypic data, I demonstrate slight population structuring among sampled localities, corresponding to three distinct sections of the river (i.e., tributary, impoundment and mainstem). However, the presence of high levels of gene flow observed among populations suggesting that both local adaptation and phenotypic plasticity may play a key role. In conclusion, M. dolomieu appears to be a successful invader that fully exploits genetic and phenotypic variability to invade, persist and establish in an array of non-native environments.
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    The ghost of introduction past : spatial and temporal variability in the genetic diversity of invasive smallmouth bass
    (Wiley Open Access, 2018) Diedericks, Genevieve; Henriques, Romina; Von der Heyden, Sophie; Weyl, Olaf L. F.; Hui, Cang
    Understanding the demographic history of introduced populations is essential for unravelling their invasive potential and adaptability to a novel environment. To this end, levels of genetic diversity within the native and invasive range of a species are often compared. Most studies, however, focus solely on contemporary samples, relying heavily on the premise that the historic population structure within the native range has been maintained over time. Here, we assess this assumption by conducting a three-way comparison of the genetic diversity of native (historic and contemporary) and invasive (contemporary) smallmouth bass (Micropterus dolomieu) populations. Analyses of a total of 572 M. dolomieu samples, representing the contemporary invasive South African range, contemporary and historical native USA range (dating back to the 1930s when these fish were first introduced into South Africa), revealed that the historical native range had higher genetic diversity levels when compared to both contemporary native and invasive ranges. These results suggest that both contemporary populations experienced a recent genetic bottleneck. Furthermore, the invasive range displayed significant population structure, whereas both historical and contemporary native US populations revealed higher levels of admixture. Comparison of contemporary and historical samples showed both a historic introduction of M. dolomieu and a more recent introduction, thereby demonstrating that undocumented introductions of this species have occurred. Although multiple introductions might have contributed to the high levels of genetic diversity in the invaded range, we discuss alternative factors that may have been responsible for the elevated levels of genetic diversity and highlight the importance of incorporating historic specimens into demographic analyses.
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    Phylogeography of the Cape girdled lizard, Cordylus cordylus : investigating biogeographic patterning in the Cape floristic region (CFR)
    (Stellenbosch : Stellenbosch University, 2013-12) Diedericks, Genevieve; Daniels, Savel R.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: In the present study I examined the phylogeography of the rupicolous Cape girdled lizard, Cordylus cordylus. Samples were collected across the species distribution range from 63 localities in the Eastern and Western Cape and Free State provinces of South Africa, yielding a total sample size of 207 specimens. Four DNA loci, two nuclear (PRLR, PTPN12) and two mitochondrial (16S rRNA, ND2), were sequenced. Bayesian inference, maximum likelihood and maximum parsimony methods were employed to test evolutionary relationships among populations, followed by population structure analyses, divergence time estimations and niche modelling. My results confirm the species monophyly and revealed the presence of two distinct clades. Clade 1 comprised specimens from the western and southern portions of the Western Cape coast, while clade 2 comprised specimens from the southern and eastern Cape coast and adjacent interior of the Eastern and Western Cape and Free State provinces. An area of sympatry between the two clades was observed in the Breede river valley. The divergence time estimates revealed an Early Pliocene (4.31 Ma), Late Miocene (6.01 Ma) divergence for each of the two clades retrieved. Phylogeographic data suggest that clade 1 is younger (lower haplotypic and nucleotide diversity), in comparison to clade 2. Furthermore, the niche modelling shows that C. cordylus occupies a wide range of unfavourable habitats. The absence of marked phylogeographic patterning within clades is very uncharacteristic for a rupicolous vertebrate species. The ecological pliability and generalist nature of C. cordylus presumably contributed to the observed phylogeographic pattern and have facilitated the absence of within clade differentiation. Moreover, I suggest that microclimatic variables, rather than geographic barriers influence the genetic structuring of C. cordylus.