Doctoral Degrees (Biochemistry)

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Browsing Doctoral Degrees (Biochemistry) by browse.metadata.advisor "Bellstedt, Dirk U."

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    Phylogenetic analyses in the african fish genus nothobranchius in relation to landscape evolution
    (Stellenbosch : Stellenbosch University, 2023-03) Van der Merwe, Pieter De Wet; Bellstedt, Dirk U.; Cotterill, Fenton P. D. ; Schliewen, Ulrich Kurt; Stellenbosch University. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: Nothobranchius is a genus of short-lived annual to semi-annual African freshwater fishes that are found in smaller seasonal ephemeral wetlands or pools and not in larger open lakes or non-seasonal river systems. The waterbodies in which they are found are situated on vertisol-type soils that have a large capacity to absorb and retain water which is slowly released upon drying. Eggs are fertilized and are deposited into the vertisol-type substrate of the waterbody. As the soil dries during the dry season cracks are formed and the eggs, which up to that point have been in an anoxic environment, are exposed to oxygen which stimulates them to develop. Several complicated pathways exist through which the eggs develop, which can lead to full development, or to several types of delayed development called diapauses. Some will remain dormant for subsequent rainy seasons ensuring that the species can survive extended droughts. Nothobranchius hatch quickly after the rainy season starts and subsequently grow very rapidly to reach maturity to repeat the life cycle. Sequencing of two mitochondrial and three nuclear genes of the majority of the species in Nothobranchius and appropriate outgroups was used to generate suitable sequence matrices which were analysed extensively using maximum likelihood and Bayesian Inference to generate robust phylogenies and dated phylogenies of the genus. A dated phylogeny was used in a biogeographic analysis to determine dispersal routes and establish that the ancestral area of Nothobranchius is in the Nilo-Sudan. Using the recently developed technique, double digest RAD sequencing, an even greater sequence data matrix of the species in Nothobranchius and appropriate outgroups was generated and analysed using the same techniques as described above. This resulted in an even more robust phylogenetic hypothesis for the genus. From this dated phylogeny landscape evolution in a tectonically active area on south central Africa could be inferred. Four key landscape evolutionary events in this area could be inferred and dated: (i) landscape warping, faulting and rifting in the Luapula river drainage, (ii), formation of the Upemba rift in the Lufira-Lualaba river drainage system, and (iii) formation of the Congo-Zambezi Watershed between the Kafue and Luapula drainage systems disrupting the ancient Palaeo-Chambeshi river drainage system, (iv) drainage of Palaeo Lake Mweru, from a previous maximum level of 1200 masl to the present-day level of 917 masl. Lastly, this research resulted in the identification of 15 new Nothobranchius species which were described in the course of this study. .