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

Abstract

This study used phylogenetic analyses of mitochondrial cytochrome b sequences to investigate genetic diversity within three broadly co-distributed freshwater fish genera (Galaxias, Pseudobarbus and Sandelia) to shed some light on the processes that promoted lineage diversification and shaped geographical distribution patterns. A total of 205 sequences of Galaxias, 177 sequences of Pseudobarbus and 98 sequences of Sandelia 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 Galaxias. Similarly, deep phylogeographic divergence was evident within Pseudobarbus, with four markedly distinct (3.8–10.0%) phylogroups identified. Sandelia 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.

Evidence of hidden diversity and taxonomic conflicts in five stream fishes from the Eastern Zimbabwe Highlands freshwater ecoregion

“…The existence of such high taxonomic diversity within a small portion of the Eastern Afromontane Region is consistent with findings from a number of previous studies that have uncovered substantial hidden diversity and narrow range endemic species (or lineages) within several stream fishes that were previously thought to have wide geographic ranges in southern Africa (e.g., Chakona et al 2013; Goodier et al 2011; Maake et al 2014; Morris et al 2015; Swartz et al 2007, 2009; Wishart et al 2006). Results of the present study thus add to the growing board of evidence that shows that a large proportion of freshwater fishes in southern Africa remain scientifically undocumented, because many river systems remain poorly explored as much of the previous research effort and application of molecular approaches has predominantly focussed on fishes of the Cape Fold Ecoregion (Ellender et al 2017).…”

“…Results of the present study thus add to the growing board of evidence that shows that a large proportion of freshwater fishes in southern Africa remain scientifically undocumented, because many river systems remain poorly explored as much of the previous research effort and application of molecular approaches has predominantly focussed on fishes of the Cape Fold Ecoregion (Ellender et al 2017). Despite being one of the geographically and taxonomically well explored regions in southern Africa, new species and deeply divergent genetic lineages continue to be discovered within almost all fish taxonomic groups of the Cape Fold Ecoregion (Chakona and Swartz, 2013; Chakona and Skelton, 2017; Chakona et al 2013, 2014; Wishart et al 2006), and estimates indicate that there are about 43 undescribed species within the 21 currently recognised fish species of this region (Linder et al 2010). The discovery of hidden diversity in the EZH freshwater ecoregion adds to the growing evidence for the existence of high species-level diversity within a number of fish species from high altitude streams in southern, east and west Africa (e.g., Friel and Vigliotta 2011; Morris et al 2016; Schmidt and Pezold 2011; Schmidt et al 2014, 2015, 2016; Thomson 2013; Thomson and Page 2010).…”

“…The continued recognition of many of the stream fishes from the EZH freshwater ecoregion as having wide geographic ranges (see Skelton 2001; Marshall 2011) demonstrates the poor taxonomic attention and lack of systematic knowledge in this region and the broader southern African subregion. Growing evidence from previous and ongoing DNA-based studies shows that many species of freshwater fishes that were previously considered to have wide geographic ranges are instead complexes comprising several genetically divergent lineages (e.g., Chakona et al 2013; Goodier et al 2011; Kramer et al 2004; Kramer and Wink 2013; Linder et al 2010; Swartz et al 2007, 2009). These studies have stimulated renewed interest in the systematics of freshwater fishes in the region as evidenced by the recent revalidation of some junior synonyms as well as the identification and description of several new species (e.g., Chakona and Swartz 2013; Chakona et al 2014; Chakona and Skelton 2017; Kramer et al 2003, 2007, 2012, 2013, 2014; Kramer and Swartz 2010; Kramer and van der Bank 2011; Maake et al 2014).…”

Biodiversity hotspots and Ocbil theory

“…'nebula' (Galaxiidae) Chakona et al (2013) x Cryptic speciation Cape sedge Tetraria triangularis (Cyperaceae: Schoeneae) Britton et al (2014) x Low genetic diversity tepui reptiles and frogs. Kok et al (2012) x Tepuihyla tree frogs Salerno et al (2015) x Vellozia hirsuta (Velloziaceae) Barbosa et al (2012) x Cattleya (Orchidaceae) Leles et al (2015) AtRf Frogs Hypsiboas albomarginatus, H. semilineatus, H. faber x Biting Midges (Austroconops (Diptera: Ceratopogonidae) Borkent and Craig (2004) x Helioporus (Myobatrachidae) frogs and others Morgan et al (2007) x trapdoor spider Moggridgea (Migidae) Cooper et al (2011) x Isopoda: Amphisopidae Gouws and Stewart (2013) Plant Soil (2012); Wood et al (2015) x x Spoon-winged lacewings (Neuroptera: Nemopteridae: Nemopterinae).…”

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

“…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).…”