Revisão da espécie Apteronotus albifrons (Teleostei: Gymnotiformes) na América do Sul: estudo filogeográfico

Abstract

The species Apteronotus albifrons (Linnaeus, 1766), a neotropical electric fish, has a wide distribution from Suriname to the south of Brazil, occurring in hydrographic basins that have been separated for more than 10 million years. This time, in evolutionary terms, would be sufficient for some differentiation between these populations. This species is part of a morphologically very similar species group, which may be distinguished from each other by discrete differences in their body pigmentation. The publications on this group have been aimed at describing new species rather than reviewing the ones already known, which results in a lack of an updated taxonomic review of A. albifrons in scientific literature. To understand the morphological and genetic variability of those populations of A. albifrons according to its geographic distribution, this study had the following objectives: perform an anatomical review of the species, use morphological and molecular data to verify whether such populations actually belong to a single species, propose a phylogeographic hypothesis to explain their peculiar distribution and tell its possible evolutionary history. We examined the external morphology of specimens identified as A. albifrons from different ichthyological collections, made osteological analyses from radiographs, sequences of the mitochondrial DNA gene COI were used to verify its genetic variability according to its locality of provenance and propose a phylogeographic hypothesis that explains such variability. There were morphological differences between the specimens, mainly in body size and pigmentation patterns, but in general these do not follow a geographic pattern. Some of the examined specimens presented diagnostic characteristics of other species, however those were randomrly mixed combinations between characteristics of A. albifrons e A. caudimaculosus. A new morphotype from the Paraná-Paraguay basin was observed, possibly belonging to a new species. The molecular analyses corroborated the hypothesis that the populations analyzed belong to the same species with geographically distinct haplotypes, despite the wide distribution of A. albifrons. Possibly such populations originated from an ancestral population that inhabited the Paleo Amazonas-Orinoco basin and would have suffered vicariant events related to the establishment of the current flow of the Amazon and Orinoco rivers in Upper Miocene and marine incursions that isolated some freshwater complexes between 5 and 4.2 Ma ago. Our results showed there are important taxonomic problems in A. albifrons and other species from its species group. Although it is possible to exist identification errors among the analyzed material, the limits between inter and intraspecific morphological variability are confusing, further studies are needed to clearly define what is A. albifrons, confirm the taxonomic validity of other species described in the last decades and understand the evolution of the species studied in the present work as well as others. There is still much to be understood about the evolution of those species so that this questions can be answerd.