Unexpected Diversity of Feeding Modes among Chisel-Mouthed Ethiopian Labeobarbus (Cyprinidae)

Abstract

Trophic resource partitioning is one of the main drivers of adaptive radiation. The evolutionary diversification of large African barbs, the genus Labeobarbus, seems to be related to mouth polymorphism. The chisel-mouthed or scraping phenotype has repeatedly evolved within Labeobarbus. At least five ecomorphs with a scraping mouth morphology were detected in the waters of the Ethiopian Highlands and can be provisionally classified into two groups: (i) “Varicorhinus”-like, and (ii) “Smiling”-like. Previously, all Labeobarbus with a scraping-mouth morphology were considered to be periphyton feeders. Using data on morphology, diet and stable isotope ratios (C and N), we addressed the question: does a scraping-mouth morphology predict feeding on periphyton? Our study revealed that five scraper ecomorphs exhibited three main feeding modes: (i) periphyton-eating, (ii) herbivory–detritivory, and (iii) insectivory. Two cases of the parallel divergence of sympatric ecomorphs with distinct feeding modes (herbivory–detritivory vs. insectivory) were revealed in two geographically isolated basins. A significant difference in δ15N values was detected among sympatric scraper ecomorphs. A periphytonophagous scraper was rich in δ15N values that are comparable with those in sympatric piscivorous fish. This data sheds light on the possibility of the utilization of periphyton as a protein-rich food by fishes.

Scale morphology is a promising, additional tool for exploring the taxonomy and ecology of freshwater fishes

“…The species list and the number of analysed scales per taxon are indicated in Table 1. To reveal the taxonomic position (order, family) and ecological characteristics (flow preference and preferred feeding habitat) of the investigated taxa, literature data (Abdurakhmanov, 1962; Cavalcante et al., 2014; Dadikyan, 1986; Derzhavin, 1937; Dresilign, 2003; Elanidze, 1983; Fricke et al., 2023; Levin et al., 2019, 2021; Nikolskiy, 1938; Reshetnikov, 2003; Sály & Erős, 2016; Turdakov, 1963) and online databases (Froese, 1990; URL1, n.d.; URL2, n.d.) were used (see Table 1 and Supplementary material).…”

Parallel trophic diversifications in polyploid cyprinid fish from East Africa: from preadaptive polymorphism to trophic specialization

“…The core of mouth polymorphism is composed of four main phenotypes (Figure 1) that were recorded throughout Africa (Worthington, 1929;1933;Matthes, 1963;Banister, 1973;Skelton et al, 1991;Nagelkerke et al, 1994): i) generalized (typical for barbs), ii) thick-lipped ('rubberlip'), iii) scraping ('chiselmouth'), and iv) large-mouthed. Mouth phenotypes are subjected to further sub-diversification and can include subtypes or variants that are recruited for occupying the new ecological niches (Levin et al, 2021b). Moreover, there are intermediate phenotypes possibly of hybrid origin (Banister, 1972;Vreven et al, 2019) that does not exclude their further specialization.…”

Speciation and repeated origins of hypertrophied lips in parallel adaptive radiations of cyprinid fish from East Africa

“…Nevertheless, the ecological role of the thick‐lipped ecomorphs in Labeobarbus is not yet known. The generalized trophic phenotype has mainly detritivorous–omnivorous diet (e.g., Levin, Komarova, et al, 2021 ; Levin, Simonov, et al, 2021 ; Matthes, 1963 ; Sibbing & Nagelkerke, 2000 ; Teshome et al, 2023 ). The feeding preferences or trophic position of the thick‐lipped ecomorph has been investigated so far for only two cases.…”