Shape diversity of the fish genus Astyanax Baird & Girard, 1854 (Teleostei, Characidae) in adjacent basins

Abstract

The Neotropical region is highly diverse in fresh water teleost fishes and extends through vast regions of South America. The genus Astyanax comprises small fish found in the tributaries and ditches of the great Brazilian basins, such as the Paraná and São Francisco Rivers. This group has been ostensibly studied from a chromosomal and molecular point of view but is still involved in problems of phylogenetic location, justifying its position incertae sedis, while having a wide diversity of forms and habitats. Our study counted on the analysis of body shape variations in seven species of the genus Astyanax and in the bimaculatus, fasciatus, and scabripinnis complexes using geometric morphometrics. We obtained images of individuals from different localities in the Paraná and São Francisco River basins, delineated two-dimensional anatomical landmarks that we then subjected to the generalized Procrustes analysis, and subsequent ordination by principal component analysis and canonical variate analysis. The results showed variation between two large groups, related mainly to variations in body height, indicating the probable existence of different evolutionarily significant units morphologically shaped by the pressure of the environment with what may be incipient speciation.