Phylogeny and biogeography of the genus Pseudobarbus (Cyprinidae) in southern Africa

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Isolation mechanisms

The waterfall that marks the lower limit of the Mohale population would have prevented upstream migration for a considerable period of time. In addition, the large geographic distances between Mohale and the eastern populations (319 – 481 km) may have led to isolation by distance. The interruption of gene flow was probably exaggerated by the lack of continuous suitable habitat and the occurrence of large native cyprinids and clariid and bagrid catfish, especially in mainstream areas. The explanation for the isolation of the Tsoelikane population is probably similar to the Mohale scenario. Large geographic distances (281 – 354 km) with intermittent suitable habitat and potential competition from large native mainstream fishes, probably interrupted gene flow, although to a lesser extent or later in the history of the Tsoelikane population compared to the Mohale population.
The hypotheses of competition avoidance and habitat preference cannot be tested directly, because of the fragmentation and isolation caused by trout and the deterioration of mainstream habitats. However, genetic structuring among redfin populations in different tributaries of the same river system, seems to be the rule rather than the exception (Bloomer & Impson, 2000; Swartz et al., 2004). This suggests that P. quathlambae, like other redfin species studied thus far, naturally prefers tributary streams. Considering the harsh environment that P. quathlambae have to endure and because they are mostly the only fish species where they occur, a hypothesis of competition avoidance might apply.

Value of the Mohale population and conservation of overall evolutionary processes

The most important evolutionary processes that must be allowed to continue within P. quathlambae are relatively simple to manage. The differentiation of the Mohale and Tsoelikane populations requires only that they remain isolated, provided that population sizeremains large. Securing the survival of the Mohale population will be difficult, however, due to the impact of the Mohale dam. This population represents a unique and divergent lineage within the species. It therefore contributes significantly to the overall genetic diversity and it is also at present the largest population. It can be considered to be an Evolutionarily Significant Unit (ESU) compared to the eastern populations according to Moritz’s (1994) definition (historically isolated and divergent) and criteria (monophyly of mtDNA and nuclear DNA frequency differences). Based on the findings of the present study and the survey of Skelton et al. (2001), several measures, including transplantation to sanctuary sites, were undertaken to conserve the Mohale population (Rall et al., 2002). Lack of differentiation at cytochrome b and inconclusive MH allele frequency differences suggest that the Tsoelikane population may not be a different ESU compared to the north-eastern populations. It should be managed in a similar way to Mohale, however, since the underlying evolutionary process
is isolation. Eradication of trout downstream will allow P. quathlambae to re-occupy its former natural distribution range in this catchment.

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Acknowledgements

The authors would like to thank Johan Rall for organising the Lesotho field surveys and for information and advice throughout the project. On these surveys Johan Rall, Denis Tweddle, Roger Bills, Mokitinyane Nthimo and Michael Cunningham helped to collect samples. Joelle van der Walt, Heidi Roos, Wayne Delport, Tyron Grant and Isa-Rita Russo are thanked for assistance in the laboratory. Michael Cunningham and Wayne Delport are also thanked for analytical advice. The Lesotho Highlands Developmental Authority Contract 1041 to the South African Institute for Aquatic Biodiversity provided the funding.

CHAPTER 1: Thesis introduction
CHAPTER 2: Population history and evolutionary processes in the critically endangered Pseudobarbus quathlambae (Teleostei, Cyprinidae), a flagship species in the highlands of Lesotho, southern Africa
Introduction
Materials and Methods
Results
Discussion
Acknowledgements .
CHAPTER 3: Sea level changes, river capture and the evolution of populations of the Eastern Cape and fiery redfins (Pseudobarbus afer and P. phlegethon, Cyprinidae) across multiple river systems in South Africa
Introduction
Materials and Methods
Results
Discussion
Acknowledgements
CHAPTER 4: Geographic genetic structure of Pseudobarbus asper and P. tenuis (Teleostei, Cyprinidae), two co-occurring sister species with differing habitat preferences in southern South Africa
Abstract
Introduction .
Materials and Methods
Results
Discussion
Acknowledgements
CHAPTER 5: Historical lineages and evolutionary processes in Pseudobarbus burchelli (Teleostei, Cyprinidae) within and among different riversystems of the south coast of South Africa
Abstract
Introduction
Materials and Methods
Results
Discussion
Acknowledgements
CHAPTER 6: Phylogeny and biogeography of the genus Pseudobarbus (Cyprinidae) in southern Africa
Abstract
Introduction
Materials and Methods
Results
Discussion
Acknowledgements
CHAPTER 7: Thesis conclusion