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?

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.

A new species of redfin (Teleostei, Cyprinidae, Pseudobarbus) from the Verlorenvlei River system, South Africa

“…n. sequenced in the present study. It shows the phylogenetic relationships among double barbeled redfins based on the mitochondrial cytochrome b data, and shows the position of the new species that is distinct from the three described double barbeled redfin species, including the three previously identified lineages of Pseudobarbus burchelli (Swartz et al 2009, 2014). The model corrected genetic distances show deep divergences (6.6–12.3%) between the new species and the other members of the double barbeled redfin group.…”

“…Specimens were assigned to four groups based on geographic origin and previous genetic results (Bloomer and Impson 2000; Swartz et al 2009, 2014; Chakona and Swartz 2013; Chakona et al 2013): Pseudobarbus skeltoni ( n =25), Pseudobarbus burchelli ( n =128), Pseudobarbus burgi (specimens from the Berg River system only; n =66) and Verlorenvlei Pseudobarbus (specimens from the Verlorenvlei River system only; n =47). A total of 47 specimens of Verlorenvlei Pseudobarbus were radiographed to count skeletal features.…”

“…Two decades later, following genetic studies and a resurgence of field surveys in the Cape Floristic Region, a new redfin species Pseudobarbus skeltoni was described from the Breede River system (Chakona and Swartz 2013), bringing the number of nominal species to eight. Based on insights from molecular studies, several other taxa of this genus remain to be described (Bloomer and Impson 2000, Swartz et al 2007, 2009, 2014, Chakona et al 2013). Herein, we describe a ninth species of Pseudobarbus from the Verlorenvlei River system, which was identified as a unique genetic lineage of Pseudobarbus burgi following a phylogeographic study by Bloomer and Impson (2000).…”

“…The Verlorenvlei and Berg lineages of Pseudobarbus burgi , three lineages of Pseudobarbus burchelli (see Chakona et al 2013 and Swartz et al 2014), and Pseudobarbus skeltoni have two pairs of oral barbels and form a monophyletic group within Pseudobarbus (Swartz et al 2009). The taxonomic history of the double barbeled redfins has been complex and confusing.…”

A review of the Pseudobarbus afer (Peters, 1864) species complex (Teleostei, Cyprinidae) in the eastern Cape Fold Ecoregion of South Africa

“…However, the lack of sharing of species between the Krom and the Gamtoos-Swart-Kabeljous is not consistent with the Palaeoriver hypothesis, as map reconstructions suggest that these four river systems would have joined before reaching the -130 m LGM sea-level (Swartz et al 2007, 2008; Figure 8b). Presence of instream physical barriers such as waterfalls or extreme ecological barriers could have prevented post-speciation range expansion between these systems, as proposed for the Breede and Heuningnes lineages of Pseudobarbus burchelli from the south-western CFE (Swartz et al 2014). Palaeoriver reconstructions suggest that the Swartkops-Coega-Baakens would have formed a common confluence before reaching the -130 m LGM sea-level, but it is uncertain whether this Palaeoriver system would have coalesced with the Sundays River system (see Swartz et al 2007; Figure 8b) due to the intervening Riy Bank (Bremner and Day 1991).…”