Browsing by Author "Teske, Peter R. (Peter Rodja)"

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    Population genetics and phylogenetic placement of the endangered Knysna seahorse, Hippocampus capensis
    (Stellenbosch : Stellenbosch University, 2003-12) Teske, Peter R. (Peter Rodja); Cherry, M. I.; Matthee, C. A.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: The aims of this study were to investigate genetic issues pertaining to the conservation of the Knysna seahorse, Hippocampus capensis, and to determine the phylogenetic placement of this endangered estuarine species among marine seahorses. This was accomplished by focusing on three aspects of the taxonomy: the interspecific level; the inter-population level; and the intra-population level. To determine which species are closely related to H. capensis, and how the evolutionary history of this lineage relates to that of other seahorses, sequence data derived from four gene fragments (the nuclear RPI and Aldolase and the mitochondrial 16S rRNA and cytochrome b genes) were used to determine the phylogenetic relationships among 30 species belonging to the genus Hippocampus. There were marked differences in the rate of evolution among these gene fragments, with Aldolase evolving the slowest and the mtDNA cytochrome b gene the fastest. Among individual partitions, the RPI gene recovered the highest number of nodes supported by >70% bootstrap values from parsimony analysis, and >95% posterior probabilities from Bayesian inference. The combined analysis based on 2317 nucleotides resulted in the most robust phylogeny. A distinct phylogenetic split was identified between the pygmy seahorse, H. bargibanti, and a clade including all other species. Three species from the western Pacific Ocean included in this study, namely H. bargibanti, H. breviceps, and H. abdominalis, occupy basal positions in the phylogeny. This and the high species richness in the region suggest that the genus probably originated in this region. There is also fairly strong molecular support for the remaining species being subdivided into three main evolutionary lineages: two West Pacific clades and a clade of species present in both the Indo-Pacific and the Atlantic Ocean, which includes H. capensis. The phylogeny obtained herein suggests that seahorses belonging to the latter clade colonised the Atlantic Ocean at least twice, once before the closure of the Tethyan Seaway, and once afterwards. Phylogenies reconstructed using mitochondrial DNA gene fragments (l6S rRNA, cytochrome band 382 bp of the rapidly evolving control region) indicate that H. capensis is closely related to an Indian Ocean lineage of H. kuda and a Red Sea lineage of H. fuscus. Other lineages closely associated with these taxa include H. kuda from the West Pacific, the East Atlantic species H. algiricus, the West Atlantic species H reidi, the East Pacific species H ingens, and the Hawaiian species H fisheri. No control region alleles were shared among H capensis and any of the marine seahorses, suggesting that the Knysna seahorse is phylogenetically distinct. The evolutionary history of H capensis, and the extent of gene flow between its three known populations, were investigated using control region sequences from 138 specimens. Most samples were obtained by taking fin clips; this method was studied on captive seahorses and no negative effects were found. Similarly high levels of genetic diversity were found in two of the wild populations (Knysna and Keurbooms Estuaries), whereas diversity in the third population (Swartvlei Estuary) was lower. Although most haplotypes are shared among at least two populations, based on the haplotype frequency distributions the three assemblages constitute distinct management units. The extant population structure of H capensis suggests that the Knysna seahorse originated in the large Knysna Estuary. The presence of seahorses in the two smaller estuaries is either the result of a vicariance event at the beginning of the present interglacial period, or colonisation of the estuaries via the sea, or a combination of the two. Population genetic parameters of the Knysna population and those of two populations of closely related marine seahorses (H kuda from the Philippines and H fuscus from the Red Sea) were similar, suggesting that the Knysna population is not genetically impoverished, despite its comparatively small area of occupancy.