Abstract:
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.
