Comparative biogeography and ecology of freshwater fishes in the Breede and associated river systems, South Africa

Distribution patterns and levels of genetic diversity in extant taxa are a product of complex palaeogeographic processes and climatic oscillations as well as the species’ intrinsic ecological adaptations. The Cape Floristic Region of South Africa presents a unique system for studying the processes that promote species diversification and distribution patterns. This region has a high degree of endemism of both terrestrial and aquatic biota and is clearly isolated from neighbouring areas by the Cape Fold Mountains and the Great Escarpment. The objective of this study was to firstly examine the ecology of freshwater fishes belonging to the genera Galaxias, Pseudobarbus and Sandelia in the south-western CFR. This was followed by an assessment of the genetic diversity of these taxa. Unique lineages were identified and their distribution was mapped. The work aimed to explore the role of the region’s complex palaeogeographic and climatic history as well as the role of the species’ ecological adaptations in driving lineage diversification and shaping contemporary distribution patterns. The four main components of the study can be summarised as follows: 1. Habitat associations of three widely distributed lineages of Galaxias zebratus Pseudobarbus burchelli and Sandelia capensis were evaluated at multiple localities in minimally disturbed mountain tributaries of the Breede, Duiwenhoks and Goukou River systems. The lineages have distinct habitat associations which were related to differences in their morphological traits. The slender-bodied Galaxias ‘nebula’ and the fusiform-shaped Pseudobarbus ‘Breede’ are capable of exploiting upper reaches with faster water velocity. By contrast, the laterally compressed Sandelia ‘eastern’ is restricted to lower reaches, making this lineage more susceptible to a wide array of impacts. 2. A recently discovered lineage of Galaxias zebratus, (Galaxias ‘nebula’), was found to be capable of tolerating emersion for a prolonged period of time. This is the first time that such capabilities have been documented in an African galaxiid. These adaptations have implications for the interpretation of Galaxias ‘nebula’s wide distribution range. 3. The phylogeography of Galaxias ‘nebula’ across its entire distribution range was investigated using two mitochondrial genes (cytochrome c oxidase subunit I (COI) and cytochrome b (cyt b)). This lineage has a complex evolutionary history that was influenced by both intrinsic and extrinsic factors. Rare events such as episodic drainage connections during Pleistocene and Holocene pluvial periods, possibly augmented by river confluences during periods of lower sea-levels and river capture events seem to be the most credible explanation for the extensive contemporary distribution and the relatively shallow genetic divergence between different river systems. 4. Mitochondrial cyt b sequences were used (i) to assess genetic diversity in G. zebratus, P. burchelli and S. capensis from the south-western CFR and (ii) to determine the roles of intrinsic ecological adaptations and extrinsic landscape and climatic changes in promoting genetic diversification and shaping present day distribution patterns of lineages in the three taxa. Marine incursions during periods of major sea-level transgressions are proposed to have isolated populations in upland refugia, thereby driving allopatric divergence in these species. Subsequent connections of rivers during wetter periods and lower sea-levels are proposed to have facilitated post-speciation dispersal of lineages to attain present day distribution patterns. While detailed morphological studies and further genetic analysis are needed to substantiate the taxonomic status of the newly discovered lineages of Galaxias zebratus, Pseudobarbus burchelli and Sandelia capensis, results of the present study indicate that the south-western CFR represents a previously unrecognised centre of freshwater fish diversity and microendemism in the broader Cape Floristic Region. Accurate identification of lineages and comprehensive mapping of their distribution is a fundamental pre-requisite for ecological studies, assessing conservation status and implementation of appropriate conservation measures

The genetic legacy of lower sea levels : does the confluence of rivers during the last glacial maximum explain the contemporary distribution of a primary freshwater fish (Pseudobarbus burchelli, Cyprinidae) across isolated river systems?

The primary freshwater fish Pseudobarbus burchelli (Smith 1841) occurs across four presently isolated river systems in the south-western cape floristic region of South Africa. Mitochondrial DNA cytochrome b (701 base pairs) and control region (601 base pairs) genes were sequenced to assess the evolutionary history of P. burchelli and evaluate the role of climatic and landscape changes in shaping patterns of genetic variation in this species. We identified three historically isolated lineages in P. burchelli: a widespread lineage that occurs across three isolated river systems and two geographically restricted lineages. The results were evaluated against predictions of the confluence of river systems during low sea levels of the last glacial maximum. Occurrence of the widespread Breede lineage in the Duiwenhoks River system is consistent with reconstructed palaeoriver systems. However, the occurrence of this lineage in the Goukou river system that formed part of the eastern Gourits–Goukou palaeoriver system can only be explained by translocation or a recent river capture or episodic inundation of low drainage divides. Extreme ecological gradients or the potential presence of instream physical barriers could have prevented an exchange of lineages between the Breede and Heuningnes river systems.Table Mountain Fund and Prince Bernhard Scholarships, the National Research Foundation (South Africa) and the Claude Leon Foundation.http://link.springer.com/journal/10750hb201

The Macroinvertebrate Communities Of Two Upland Streams In Eastern Zimbabwe With Reference To The Impact Of Forestry

Benthic macroinvertebrates and physico-chemical parameters of the water were examined from two fast flowing streams, the Nyahode River which drains a pine monoculture catchment and the Haruni River which drains an undisturbed deciduous forest catchment in the Chimanimani Mountains, Eastern Zimbabwe. Benthic samples and environmental data were collected in October 2004, December 2004 and January 2005. The water quality was similar in many respects but turbidity was significantly higher (p<0.05) in the Nyahode River compared to the Haruni River (mean 17.1 NTU and 6.0 NTU respectively). Conductivity was almost three times higher in the Nyahode (66 µS cm-1) than the Haruni (24 µS cm-1). The impact of forestry on faunal composition was evident on Ephemeroptera (Euthraulus, Afronurus and Dicercomyzon), Plecoptera (Neoperla spio) and Trichoptera (Macrostemum capense) (EPT) richness. Absence of shredders from both streams is a result of the low retention of Course Particulate Organic Matter (CPOM) in the streams due to the rapid flows whilst dominance of filterers suggests that the retention of organic material seems to be limited to Fine Particulate Organic Matter (FPOM). These results indicate that unless reference conditions are established first, results from biotic indices could be completely misleading because absence of some taxa could not be due to human impact but is just a natural phenomenon. Many of the taxa collected from both rivers were sensitive to water quality change (ASPT, 5.6 to 7.8) indicating good water quality which is attributable to the currently underdeveloped nature of the catchment

Deep genetic divergence between geographically isolated populations of the goldie barb (Barbus pallidus) in South Africa: potential taxonomic and conservation implications

Barbus pallidus as it is presently defined has a disjunct distribution that is divided between northern and southern populations in South Africa. Sequence data from the cytochrome b gene region showed two distinct lineages that correspond to these geographically distant areas. Divergence between these two lineages was relatively high (5.5–6.5%) and comparable to typical interspecific divergences found between closely related southern African cyprinid fishes. Based on this deep genetic divergence, we conclude that the northern lineage may represent a previously unrecognised species or may belong to a different, but known species or species complex not associated with ‘true’ B. pallidus. These findings add to a growing body of evidence that freshwater fish diversity in southern Africa requires major revision.Keywords: cryptic diversity, Cyprinidae, disjunct distribution, taxonom

Evolutionary Drivers of Diversification and Distribution of a Southern Temperate Stream Fish Assemblage: Testing the Role of Historical Isolation and Spatial Range Expansion

<div><p>This study used phylogenetic analyses of mitochondrial cytochrome <i>b</i> sequences to investigate genetic diversity within three broadly co-distributed freshwater fish genera (<i>Galaxias</i>, <i>Pseudobarbus</i> and <i>Sandelia</i>) to shed some light on the processes that promoted lineage diversification and shaped geographical distribution patterns. A total of 205 sequences of <i>Galaxias</i>, 177 sequences of <i>Pseudobarbus</i> and 98 sequences of <i>Sandelia</i> from 146 localities across nine river systems in the south-western Cape Floristic Region (South Africa) were used. The data were analysed using phylogenetic and haplotype network methods and divergence times for the clades retrieved were estimated using *BEAST. Nine extremely divergent (3.5–25.3%) lineages were found within <i>Galaxias</i>. Similarly, deep phylogeographic divergence was evident within <i>Pseudobarbus</i>, with four markedly distinct (3.8–10.0%) phylogroups identified. <i>Sandelia</i> had two deeply divergent (5.5–5.9%) lineages, but seven minor lineages with strong geographical congruence were also identified. The Miocene-Pliocene major sea-level transgression and the resultant isolation of populations in upland refugia appear to have driven widespread allopatric divergence within the three genera. Subsequent coalescence of rivers during the Pleistocene major sea-level regression as well as intermittent drainage connections during wet periods are proposed to have facilitated range expansion of lineages that currently occur across isolated river systems. The high degree of genetic differentiation recovered from the present and previous studies suggest that freshwater fish diversity within the south-western CFR may be vastly underestimated, and taxonomic revisions are required.</p></div

Mean and range of model-corrected genetic divergence (%) between <i>Pseudobarbus</i> lineages from the south-western CFR.

<p>The ranges of the values are given in parentheses. Within lineage divergences are given in bold. Fu’s <i>F</i>s value for each lineage is given in the last column (** <0.005; *<0.05).</p