Integrative taxonomy reveals hidden diversity in the southern African darters genus Nannocharax Günther 1867 (Characiformes: Distichodontidae)

Abstract

The present study explored the diversity of Nannocharax within southern Africa by implementing three species delimitation methods for a data set consisting of 37 mitochondrial cytochrome oxidase subunit I sequences. Two unilocus coalescent methods, the General Mixed Yule Coalescent (GMYC) and the Bayesian implementation of the Poisson Tree Processes (bPTP), and a genetic distance method, the Automatic Barcode Gap Discovery (ABGD), were applied. Both GMYC and bPTP delimited the same operational taxonomic units (OTUs), revealing a higher diversity for the genus in the region than previously recognised, whereas the ABGD failed to delimit the same candidate species. All methods delimited two species groups, and these are supported based on colouration patterning and morphology; the Nannocharax multifasciatus and the Nannocharax macropterus species groups and the delimited OTUs were assigned to each. Two putative new species were identified, Nannocharax cf. lineostriatus "Okavango" from the Okavango River in Angola and N. cf. lineostriatus "Kwanza" from the Kwanza River system in Angola. The distribution of Nannocharax dageti was confirmed for the Upper Zambezi and extended to the Okavango system, and an identification key for the southern Africa Nannocharax species is provided.

Revision of Nannocharax luapulae Boulenger, 1915 (Characiformes: Distichodontidae) from the Upper Congo basin: Evidence for a species pair

“…(2014), N. hastatus by Jerep & Vari (2014) and N. hadros (Katemo Manda et al ., 2021)], one from the Ouémé basin in West Africa [ N. signifer by Moritz (2009)] and two from the Cross basin in Lower Guinea [ N. usongo and N. zebra by Dunz & Schliewen (2009)]. Most recently, the diversity of Nannocharax in southern Africa has been studied, with the identification of two species potentially new to science, and an updated identification key has been presented (Bragança et al ., 2020).…”

“…Distichodus affinis Günther 1873 and Neolebias ansorgii Boulenger 1912 were chosen as outgroup species due to the availability of COI sequences on GenBank and because these distichodontids were also used as outgroup taxa to Nannocharax in Bragança et al . (2020) (Figure 2).…”

“…Species forming two clades, based on the current identification of included specimens, have been referred to by _1 for the clade closest to the type hydrographic (sub)unit, or in the case of N. dageti considered conspecific according to Bragança et al . (2020), and _2 for the one further beyond (see Supporting Information Table S1 for more details). All are marked by *.…”

“…Furthermore, in this south-eastern part of the DRC, there is geological evidence about past hydrographic connections between the Upper Lualaba-Lufira drainage, occupied by N. chochamandai, and the Luapula basin, occupied by N. luapulae, which once were both part of the so-called Palaeo-Chambeshi drainage system (Moore et al, 2012). It was the Palaeo-Kafila River that connected these two basins (Cotterill, 2004; the identification of two species potentially new to science, and an updated identification key has been presented (Bragança et al, 2020).…”