Genetic diversity in the anabantids Sandelia capensis and S. bainsii: A phylogeographic and phylogenetic investigation

Abstract

This study concerns the phylogeography of Sandelia capensis and S. bainsii (family Anabantidae), two freshwater fish species endemic to Cape coastal rivers of South Africa. The mitochondrial DNA (mtDNA) cytochrome b gene (S. capensis) and control region (S. capensis and S. bainsii) were used as genetic markers. Sandelia capensis has a wide distribution, and occurs in most river systems of the Cape Floristic Region (CFR). Therefore, by studying the genetic variation within the species we could investigate the drainage history of this region. Two major historically isolated lineages were identified within this species, one comprising west coast populations and the other south coast populations. Genetically unique lineages were also identified within each of these two major clades. The split between the two major clades dated back to the Pliocene, while divergence times for lineages within them dated back to the Pleistocene. River capture events and sea level changes in the CFR played a major role in shaping the genetic variation that we observe within S. capensis today. Sandelia bainsii is restricted to a few Eastern Cape coastal rivers, and is classified as endangered. Within this species two divergent clades were identified, a Great Fish/Kowie lineage and a Buffalo/Gulu lineage. Sandelia capensis is also of conservation importance since certain populations are declining as a result of many different threats. In identifying these genetically unique lineages, certain areas (rivers/populations) could be prioritized for conservation management. The two major lineages identified within each of the two species should be conserved as separate units and not be intermixed. Two genetically very unique populations identified within S. capensis, the Heuningnes and Diep, are under severe pressure and should also be prioritized for management. In addition, a preliminary phylogenetic study was performed on the Anabantidae using mtDNA 16S rRNA sequences. This was done to investigate the phylogenetic relationships between the two Sandelia species (classified as sister taxa) and also their relationships with the other anabantids. The phylogenetic relationships between the anabantids were largely unresolved, probably due to an ancient radiation.