From taxonomic deflation to newly detected cryptic species: Hidden diversity in a widespread African squeaker catfish

Dagmar Jirsová,John O Malala,Zuheir N Mahmoud,Radim Blažek,Jan Štefka,Miloslav Jirků,David E Lotuliakou

doi:10.1038/s41598-019-52306-2

Abstract

Cryptic genetic diversity and erroneous morphological species determination represent frequent problems in biodiversity research. Here, examination of 138 specimens of Synodontis (Mochokidae, Siluriformes) from the Nile River and Lake Turkana revealed the presence of both S. schall-like and S. frontosus-like morphotypes, with a phenotypic gradient between them. We concluded phylogenetic and population genetic analyses based on two mitochondrial and one nuclear marker including 131 coxI (565 bp), 96 cytb (973 bp) and 19 RAG2 (896 bp) sequences from the Nile-Turkana population, plus additional GenBank data of Synodontis spp. Whilst nuclear data were inconclusive, mitochondrial sequences suggested that both morphotypes and intermediate forms are conspecific. The results imply probable synonymy of S. frontosus with S. schall. Conversely, a strong biogeographical signal was revealed among widely distributed and supposedly conspecific S. schall-like catfish of the Nilo-Sudanian ichthyological province. Synodontis schall sensu stricto (=Eastern clade), as defined by type locality in the Nile, is apparently restricted to the eastern part of the Nilo-Sudanian ichthyological province (e.g. Nile, Turkana, Chad). Synodontis schall Western clade (Senegambia, Niger, Chad) most probably represents a cryptic taxon, unrecognized thus far due to the absence of distinctive morphological differences.

Highlights

Cryptic genetic diversity and erroneous morphological species determination represent frequent problems in biodiversity research
Within the scope of research on fish parasites in the Nile River and Lake Turkana, we examined a total of 138 Synodontis specimens
The two species might co-occur in both basins, S. frontosus is considered absent in Lake Turkana itself, reportedly being restricted to its main source, the Omo River[22]

Summary

Introduction

Cryptic genetic diversity and erroneous morphological species determination represent frequent problems in biodiversity research. The main contributing factor to the undiscovered cryptic diversity of some species is the lack of clear distinguishing morphological features in combination with the absence of relevant molecular data[3]. This underestimates the species richness and limits our understanding of species geographical distribution. The two species might co-occur in both basins, S. frontosus is considered absent in Lake Turkana itself, reportedly being restricted to its main source, the Omo River[22] Diagnostic features of both species are similar and partly overlapping, distinguishing between the two in the field is difficult

Methods

Results

Discussion

Conclusion