Genetic analysis of the widely distributed species Knodus Moenkhausia (Characiformes: Characidae). Is it a unique species?

Abstract

The Knodus genus is allocated as incertae sedis in the Characidade family and comprises 27 species, but its validity has been questioned. In the phylogenetic studies conducted that included the Knodus genus, it was paraphyletic. In addition, the number of species remain uncertain. Knodus moenkhausii is a specie widely distributed occurring in Paraguai, Alto Paraná and São Francisco basins. It is a small fish that inhabits small streams. The identification of this species is difficulty due its similarity with other species of genus and even others related genus. The wide geographic distribution of this species takes a question if this species is a unique evolutionary unit or actually comprises a species complex. In recent years, the use of molecular tools to identify species has been shown to be promising and effective, also revealing a large number of new species. In 2003, it was proposed a standardized method to molecular identification of species, named DNA barcoding. The method showed extremely effective (>90%), revealing also a large hidden biodiversity. Thus, front of the fact of Knodus moenkhausii to be a small fish widely distributed, occurring in different hydrographic basins; the difficulties to identification; the few studies about the real number of species to this genus and the promising use of molecular tools to identify cryptic species, the aim of this project is to assess specimens identified as Knodus moenkhausii from all geographical area that it occur to test the hypothesis of this species represent more than one evolutionary unit. (AU)