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.

Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 611 37 Brno Czech Republic

Department of Zoology Faculty of Science University of Khartoum 111 15 Khartoum Sudan

Faculty of Science University of South Bohemia Branišovská 1760 370 05 České Budějovice Czech Republic

Institute of Parasitology Biology Centre Czech Academy of Sciences Branišovská 31 370 05 České Budějovice Czech Republic

Institute of Vertebrate Biology Czech Academy of Sciences Květná 8 603 65 Brno Czech Republic

Kenya Marine and Fisheries Research Institute Lake Turkana Station P O Box 205 30500 Lodwar Kenya

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Sci Rep. 2019 Dec 20;9(1):19907. doi: 10.1038/s41598-019-56348-4. PubMed

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