Unraveling patterns of intraspecific variations in the diet and morphological traits of Apareidon vladii Pavanelii 2006, a threatened Neotropical freshwater fish

We described the between–individual variations and compared the diet and morphology of Apareiodon vladii Pavanelli 2006 populations from three rivers in protected areas, South Brazil. Body shape variables and trophic traits were used to describe the morphology of the species and stomach contents were analyzed using volumetric and Utermöhl methods to quantify the microalgae. The diet consisted of periphytic algae, bryophytes and aquatic insects, being Cyanophyceae, Bacillariophyceae and Mediophyceae indicators of fish diet. Diet and body shape differed significantly among fish river populations. A more dorsally curved body was the main trait distinguishing individuals of the Laranjeiras River. The significant relationships between body/trophic morphology and diet revealed that individuals who consumed Bacillariophyceae tended to exhibit greater inter–gill raker spacing. Otherwise, lower intestinal coefficient was verified for Muquilão River individuals, who also exhibited more specialized diets. High variations and nested diets were recorded between general and local site individuals, indicating that specialized diets comprise a subset of these populations’ diets. In general, A. vladii showed streamlined body and algivorous diet, however, the species display different individual trophic patterns based on local ecological contexts. These findings demonstrate how individual differences may allow coexistence in the face of environmental changes.