The morphology and morphometry of otoliths have emerged as powerful indicators of ecological characteristics of fishes. However, shape descriptors that can accurately predict well-documented functions played by species in tropical ecosystems are either restricted to a few groups or poorly known. Therefore, we evaluated the power of two otolith shape descriptors (ecomorphological indexes and Fourier harmonics) in discriminating trophic and depth strata preference groups of tropical fish species. Differences in otolith shape of ecological groups were visualized by linear discriminant analysis (LDA), and tested by a jack-knife cross-validation method and permutational multivariate analysis of variance (PERMANOVA) for both methods. Visually and statistically, both descriptors were good predictors of trophic groups and depth preference categories (PERMANOVA, p < 0.05). Overall jack-knifed classification success between both descriptors were very similar, with harmonics correctly classifying 90.38% of assigned trophic groups and 75.96% of given depth preference categories, against 82% and 56.25% of ecological indexes, respectively. Our results suggest that Fourier descriptors and ecomorphological indexes of otoliths should be used as functional traits in future studies, as otolith shape provides a wider range of ecological information regarding feeding habitat, mobility, substrate association and water column use.
Based on morphological and molecular analysis of Astronotus species, a new species is described from the Orinoco River and Gulf of Paria basins in Venezuela and Colombia. Morphologically, it differs from Astronotus crassipinnis and Astronotus ocellatus in pre-orbital depth, caudal peduncle depth, head width, and caudal peduncle length, with significant differences in average percentage values. Osteologically, it differs from the two described species by lacking a hypurapophysis on the parahypural bone (hypural complex) and having two or three supraneural bones. Another characteristic that helps diagnose the new species is the morphology of the sagitta otolith, which is oval with crenulated dorsal and ventral margins and a rounded posterior edge. Genetically, the new species is distinct from all the other lineages previously proposed for the genus, delimited by five single locus species delimitation methods, and also has unique diagnostic nucleotides. Phylogenetic analyses support the monophyly of the new species as well as all other species/lineages. Astronotus species have considerable genetic, anatomical, and sagitta otolith shape differences, but have few significant traditional morphometric and meristic differences, because there is high variability in counts of spines, soft dorsal-fin rays, and lateral-line scales. It is clear that this new species is genetically and anatomically differentiated from all other species within the genus, and deserves recognition as a new valid species.
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