Trophic divergence
Diet. Food spectra of sympatric ecomorphs of Labeobarbusspp. were rather diverse and composed of i) detritus, ii) invertebrates (mainly insects: Ephemeroptera, Hemiptera, Trichoptera, Coleoptera, Hymenoptera, and Diptera), iii) macrophytes (remnants of helophytic and semi-aquatic plants, represented by seeds, leaves, stems, and flower parts, sometimes coupled with filamentous algae), and occasionally iv) fish (juvenile parts or scales). Feeding of sympatric ecomorphs in all four rivers studied was divergent but at various degree as estimated by index of relative importance (Fig. 3B).
Detritus was the main component among food items in both generalized (63.8-92.1%) and thick-lipped ecomorphs (27.1–79.0%) (Fig. 3B). Generally, the diet of the thick-lipped ecomorph was more insectivorous compared to generalized ecomorph in all rivers studied (Figure 3B). Invertebrates in the diet of both ecomorphs were represented by larvae of Ephemeroptera and Trichoptera, larvae and imagoes of Diptera and Coleoptera as well as imagoes of Hemiptera, and Hymenoptera. Contributions of invertebrates for fish feeding might be underestimated due to their quick digestion. This is why we also provide data on N and C stable isotope composition (see below). Detailed description of the diet of each ecomorph in certain rivers see in Supplementary material S4.
Stable Isotope Composition.Basic statistics for both δ15N and δ13C values is given in Supplementary Table S5. The thick-lipped ecomorph had higher δ15N values that generalized one in all comparisons with statistically significant difference in four of six paired comparisons: Birbir, p < 0.05; Didessa, p < 0.01; Gojeb, p < 0.01; and Sore, p < 0.05 (Fig. 4 and Supplementary Fig. S6). When significant, the difference in mean δ15N values between sympatric generalized and thick-lipped ecomorphs varied from 1.9‰ (Didessa) to 0.9‰ (Sore). Significant differences in δ13C values between sympatric pairs were found in the Didessa, Gojeb, and Sore Rivers. In all these cases, the lipped ecomorph had higher δ13C values (the difference varied from 1.6‰ to 1.2‰).