Ecological speciation within the mormyrid genus Campylomormyrus resulted in sympatric species exhibiting divergence in their feeding apparatus and electric organ discharge (EOD). This study documents the overall diet of the genus Campylomormyrus and examines the hypothesis that Campylomormyrus radiation is caused by an adaptation to different food sources. We performed diet assessment of five sympatric Campylomormyrus species (C. alces, C. compressirostris, C. curvirostris, C. tshokwe, C. numenius) and their sister taxon Gnathonemus petersii with markedly different snout morphologies and EODs using hybrid capture/HTS DNA metabarcoding of their stomach contents. Our approach allowed for high taxonomic resolution of prey items, including benthic invertebrates, allochthonous invertebrates, and vegetation. Comparisons of the diet compositions using quantitative measures and diet overlap indices revealed that all species are able to exploit multiple food niches in their habitats, i.e., fauna at the bottom, the water surface, and the water column. Major part of the diet is larvae of aquatic insects, such as dipterans, coleopterans, and trichopterans, known to occur in holes and interstitial spaces of the substrate. The results showed that different snout morphologies and the associated divergence in the EOD translate into different prey spectra. This suggests that the diversification in EOD and the morphology of the feeding apparatus is under functional adaptation.

Ecological speciation within the mormyrid genus Campylomormyrus resulted in sympatric species exhibiting divergence in their feeding apparatus and electric organ discharge (EOD). This study provides direct evidence to support the suggested ecological speciation scenario that Campylomormyrus radiation is caused by an adaptation to different food sources. We performed diet assessment of sympatric Campylomormyrus species with markedly different snout morphologies and EODs using hybrid capture/NGS DNA metabarcoding of their stomach contents. Our approach allowed for high taxonomic resolution of prey items, including benthic invertebrates, allochthonous invertebrates, and vegetation. Comparisons of the diet compositions using quantitative measures and diet overlap indices revealed that all species are able to exploit multiple food niches in their habitats, i.e. fauna at the bottom, the water surface, and the water column. The major part of the diet is larvae of aquatic insects, such as dipterans, coleopterans, and trichopterans, known to occur in holes and interstitial spaces of the substrate. The results showed that different snout morphologies and the associated divergence in the EOD translate into different prey spectra. This suggests that the diversification in EOD and the morphology of the feeding apparatus is under functional adaptation.