Browsing by Author "Gouws, Gavin"

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    The biogeography, systematics and conservation of Phreatoicidean isopods in South Africa
    (Stellenbosch : University of Stellenbosch, 2004-12) Gouws, Gavin; Cook, B. A.; Matthee, C. A.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology
    ENGLISH ABSTRACT: Historically, isopods of the suborder Phreatoicidea were thought to be represented in southern Africa by four species belonging to the endemic genus Mesamphisopus. This taxonomy was based on poor collections and the extent of variation among and within populations were poorly understood. In the present study, intensive sampling was undertaken to determine the diversity, distribution and biogeography of phreatoicidean isopods within South Africa. Analyses of allozyme data and mitochondrial DNA sequences (from the 12S rRNA and protein-coding COI genes) were used to examine differentiation among populations, extricate species boundaries (in combination with morphometric and morphological data) and to elucidate the evolutionary relationships among taxa. Additionally, conservation units were identified among the sampled populations and conservation threats highlighted. First, genetic and morphometric differentiation was examined among populations identified morphologically as M. capensis. Collection localities spanned two mountainous regions in the Western Cape and these were separated by a coastal plain remnant. Five morphometrically and genetically distinct species were identified. These taxa are also geographically partitioned in two regions, which were regarded as Evolutionarily Significant Units. Differentiation among populations of the two regions, and similar patterns in other taxa, was attributed to Cenozoic sea-level fluctuations. Second, populations, variably assigned to M. abbreviatus or M. depressus, were examined to determine whether they were conspecific. A large geographic area was sampled to account for intraspecific differentiation. Limited morphometric discrepancies were observed, with individual populations being either similar to the M. abbreviatus or the M. depressus syntypes. Genetic support for the recognition of a cryptic species complex among the sampled populations was equivocal. Substantial genetic differentiation and a lack of gene flow were observed among all populations. Clear patterns of isolation by distance were not detected, and genetic structure appeared to be unrelated to geography or drainage systems. The mosaic pattern of relatedness among populations was best explained by stochastic demographic processes, such as extinction-recolonization events or population bottlenecks.Thirdly, detailed taxonomic descriptions and illustrations of six new species, identified genetically and morphometrically among the populations included in the above analyses, were provided. These species were largely distinguished from each other, and the four original species, using a combination of setation, mouthpart, pleopod and uropod features. Lastly, phylogenetic relationships among all ten recognized Mesamphisopus species, and an additional unresolved group of populations, were examined. MtDNA data partitions and a recoded allele frequency matrix were analysed independently and in combination. Topologies indicated unrecognized species-diversity within an unresolved group of populations. Evolutionary relationships, the identification of six biogeographic centres, and the dating of divergences using a relaxed Bayesian clock suggested that differentiation and speciation within Mesamphisopus was largely allopatric or vicariant and driven by Mesozoic sea-level and climate change. Chance long distance dispersal events would, in turn, explain spurious phylogenetic relationships and distributions. This study contributes significantly to the understanding of the diversity and the conservation of the little-studied southern African freshwater invertebrates. Moreover, this study is the first to investigate genetic and morphometric differentiation, and phylogenetic relationships, below the generic level within the Phreatoicidea; thus establishing a methodological and theoretical framework for species delineation and the accurate determination of biodiversity within individual phreatoicidean genera.
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    MicroCT imaging applied to description of a new species of Pagurus Fabricius, 1775 (Crustacea: Decapoda: Anomura: Paguridae), with selection of three-dimensional type data
    (Public Library of Science, 2018) Landschoff, Jannes; Komai, Tomoyuki; Du Plessis, Anton; Gouws, Gavin; Griffiths, Charles L.
    A new species of hermit crab, Pagurus fraserorum n. sp. (family Paguridae) is described from rocky subtidal reefs off KwaZulu-Natal, South Africa, and illustrated using both conventional drawings and colour photographs, and via three-dimensional (3D) X-ray micro-computed tomography (μCT). Because of the limitation μCT has in detecting very fine and soft structures, a novel approach of manually drawing setation and spinulation onto the twodimensional images of the 3D visualizations was used to illustrate the pereopods. In addition, an interactive figure and rotation movie clips in the supplement section complement the species description, and the 3D raw data of the 3D type data are downloadable from the Gigascience Database repository. The new species is the sixth species of Pagurus Fabricius, 1775 reported from South Africa and is closely allied to the Indo-Pacific P. boriaustraliensis Morgen, 1990 and P. pitagsaleei McLaughlin, 2002, from which it differs by its shorter ocular peduncles, by the armature of the carpus of the right cheliped, and also in colouration. This study presents the first description of a hermit crab in which a majority of taxonomic details are illustrated through 3D volume-rendered illustrations. In addition, colour photographs and COI molecular barcodes are provided, and the latter compared to COI sequences of specimens from Western Australia previously identified as P. boriaustraliensis and of specimens of P. pitagsaleei from Taiwan, as well as to three additional South African members of the genus. The South African taxon was confirmed to be genetically distinct from all species tested.