Morfologia adaptativa de Cichla monoculus Spix e Agassiz, 1831 (Cichliformes: Cichlidae): trade-off de um predador visual em águas amazônicas

Abstract

In the Amazon Basin, studies have associated intraspecific variations observed in fish species with the types of waters of Amazonian aquatic ecosystems, which are historically classified as clear, black, and white according to their coloration. These water types differ greatly in their physicochemical characteristics, and therefore, it is expected that fish would have phenotypes adapted to the local conditions of each water type. Among the restrictive limnological variables is water transparency, since it causes differences in the transmission of wavelengths in aquatic environments, and can affect the structure, shape, and consequently the evolution of fish that depend on vision for foraging and reproduction behaviors. The present study aims to investigate the adaptive morphology of the visual predator Cichla monoculus in lakes of two Amazonian water types in Tefé (AM) region: whitewater and blackwater. We employed traditional and geometric morphometric methodologies to assess variations in body shape and counts of the lateral line scales to compare the groups. Two linear measurements, the orbit diameter and head length, were statistically different between the groups, with black water peacock basses having higher allometric coefficients. Statistical differences in mean morphological shape, morphological disparity, and the number of lateral line scales were also observed between the groups, with white water peacock basses showing greater morphological disparity and more lateral line scales on average. Our data support the hypothesis that Amazonian water types are important sources of selective pressure on body shape and lateral line morphology of C. monoculus and that compensations between sensory systems occur to facilitate adaptation in divergent habitats.