Karyotypic Diversity and Evolutionary Trends in Neotropical Electric Fish of the Genus (Gymnotiformes: Gymnotidae).

Electric fish of the order Gymnotiformes are endemic to the Neotropical region, and their highest diversity is observed in the Amazon region. The family Gymnotidae, which consists of the genera and , is a natural group and is located at the base of the phylogeny of the order. is a widely distributed and specious genus with high karyotypic diversity, especially concerning to the diploid number and the locations of repetitive sequences. Our karyotyping results in five species of the family Gymnotidae (, cf. , cf. , , and "Maranhão") corroborate the proposal of plasticity of the diploid number in this group. Moreover, in this study, we propose that the (rDNA) sequences were species-specific markers that act as a potential biogeographical marker for the genus. Besides, the sequence's location, particularly in . from Central Amazon, shows a close relationship with of the species, with 54 chromosomes, from the Paraná-Paraguay basin in the Center-South of Brazil. Considering that the ancestral diploid number for Gymnotidae is 52 chromosomes, we also suggest that the trend in the family is toward a decrease in the chromosome number. However, the clade stands out in this regard, with an increase and a decrease in chromosome number; this pattern may be reinforced with the ecologic behaviors and the geodispersal patterns of this clade.