Deep genetic and morphological divergence in the Hippopotamyrus ansorgii species complex (Teleostei: Mormyridae) in southern Africa

Abstract

The present study used molecular and morphological approaches to investigate hidden diversity within the Hippopotamyrus ansorgii species complex in southern Africa.Phylogenetic reconstructions and three species delimitation methods based on two mitochondrial markers (cytochrome b and cytochrome oxidase I) and one nuclear marker (S7) revealed 12 Molecular Operational Taxonomic Units (MOTUs), with two of them representing two recently described species, Hippopotamyrus longilateralis and Hippopotamyrus szaboi. The highest diversity occurred in the Kwanza River system, which contained five MOTUs, and the Upper Zambezi River system that had two MOTUs. Five other river systems contained a single MOTU each. A major impediment to the review of this complex has been the uncertainty surrounding the type locality of the specimens that were used for the description of H. ansorgii. The present study has, through a careful examination of published literature and synthesis of information on the travel activities of Dr. William Ansorge who collected the specimens, identified the Kwanza River system as the most plausible source of the syntypes. The resolution of the type locality of H. ansorgii facilitates future work on the review of this complex which is critical for providing reliable biodiversity estimates, identifying effective conservation management strategies and understanding the evolutionary history and biogeographic patterns of the fishes of this region.

Biogeographic and β-diversity patterns for southern Africa’s native freshwater fishes: a synthesis

“…More recently, taxonomic work on ichthyofaunas of the Cape Fold Freshwater Ecoregion (Ellender et al 2017), the Eastern Zimbabwe Highlands Freshwater Ecoregion ) and several drainage basins in southern Africa (Mutizwa et al 2021), have all revealed the presence of species complexes and previously unrecognized diversity in several genera, including Hippopotamyrus, Galaxias, Pseudobarbus, Sandelia, Amphilius, Zaireichthys and Chiloglanis. Similarly, molecular phylogeny studies have exposed previously unrecognized diversity in the cyprinid genus Enteromius (Schmidt et al 2017, Van Ginneken et al 2017.…”

Mitogenome recovered from a 19th Century holotype by shotgun sequencing supplies a generic name for an orphaned clade of African weakly electric fishes (Osteoglossomorpha, Mormyridae)

“…Based on results of previous phylogenetic studies of Mormyroidea (Sullivan et al 2000;Peterson et al 2022) the tree was rooted with Myomyrus macrops. To this alignment we added the Cyt-b sequences from NMW 22417, the P. tavernei and Inkisi River specimens, plus previously published Cyt-b sequences of HaSC species and populations from Kramer et al (2004), Kramer andSwartz (2010), andMutizwa et al (2021) as well as new sequences from H. szaboi-like forms from the Kabompo River, a large left-bank affluent of the upper Zambezi in Zambia. As analyzed, this dataset included sequences from 113 individuals.…”

“…Reticence of taxonomists to use either this specific or generic name during the past 150 years may be due to the holotype's unusually short caudal peduncle that places its morphometric ratios outside the range of most other specimens as well as its imprecise type locality. Nonetheless, we suspected H. pauciradiatus might be related to the species of the HaSC both because of general phenotypic similarity and its geographic provenance: we know the freshwaters of Angola to be particularly rich in forms belonging to this mormyrid clade, many still undescribed (Mutizwa et al 2021). If indeed H. pauciradiatus and the HaSC constitute a monophyletic group within Mormyridae, the former could provide the generic name the latter require.…”

“…The "Hippopotamyrus ansorgii species complex" (HaSC) is an informal term used to denote Hippopotamyrus ansorgii (Boulenger, 1905) plus three more described and additional undescribed species of mormyrid weakly electric fishes known in anglophone southern Africa as "slender stonebashers" (Kramer et al 2004;Chakona et al 2018;Mutizwa et al 2021). Previous analyses of DNA sequence data have shown that these species, while a monophyletic group, are not close relatives of Hippopotamyrus castor Pappenheim, 1906, the type species of Hippopotamyrus Pappenheim, 1906 from Cameroon, but are instead the sister group to a very large clade of mostly Congo Basin species placed in genera Marcusenius Gill, 1862, Gnathonemus Gill, 1863, Campylomormyrus Bleeker, 1874, Genyomyrus Boulenger, 1898, and Cyphomyrus Myers, 1960(Sullivan et al 2016Peterson et al 2022).…”

“…In contrast to H. pauciradiatus, many specimens have been identified (rightly or wrongly) to the taxon Hippopotamyrus ansorgii (Boulenger, 1905) during the past 117 years, although it is also a species with an uncertain type locality. However, in a recent study Mutizwa et al (2021) examined the field notes of the collector of H. ansorgii's two syntypes and concluded that they must have been taken in the Kwanza River basin of Angola, a system in which the same authors identified five distinct mitochondrial lineages of the HaSC, associated with different morphotypes. Mutizwa et al (2021) informally named these K1 through K5 without determining which if any of them correspond to H. ansorgii sensu stricto, or if one of these might correspond to the odd-looking holotype of H. pauciradiatus, a fish that may or may not have come from the Kwanza.…”