Validação do dna barcoding como identificador de espécies: um estudo de ampla amostragem com o gênero pseudoplatystoma (siluriformes; pimelodidae) na Amazônia

Abstract

DNA Barcoding is a methodology in which one assumes that a small fragment of DNA can be used as a standard and unique identifier, such as a barcode for species identification, serving both in the identification of species already described, and in assisting in discovery of new species. The main precondition for its effectiveness is that intraspecific differences are always smaller than interspecific, which is called the barcoding gap. The reciprocal monophyly of species would then be the main determinant for its existence. Among the factors that will determine the existence of reciprocal monophyly and hence efficiency of DNA Barcoding are intraspecific diversity and population structure. Few empirical tests of DNA Barcoding were undertaken to validate it and its premises. In this study we used a genus of Neotropical fishes as a model for validating DNA Barcoding. In the first series of tests we used a database that contained only sequences from samples with references to images. This yielded 100% correct identification identifications between a priori identification and a posteriori identification based on DNA Barcoding. Thus we can confidently use DNA Barcoding for the a posteriori identification of samples without reference to images or even samples of unknown origin. In the second set of tests unreferenced sequences were added to database; the sequence database totaled 229 samples. In this study we obtained 91.26% correct identification of a priory identified species. The apparent inefficiency of DNA Barcoding has been attributed to errors in identifying specimens a priori because of the reliability of the first database, the high confidence values that support the clades in the first analysis, and the clear presence of the barcoding gap. All species of Pseudoplatystoma proved to be monophyletic and intraspecific differences were always lower than the interspecific, i.e. the barcoding gap was observed in all cases. Thus, this study contributes to the validation of the efficacy of DNA Barcoding in identifying species, especially fishes, in the Amazon basin.