Molecular assessment of Gymnotus spp. (Gymnotiformes: Gymnotidae) fishing used as live baitfish in the Tietê River, Brazil

The barcode trap-Description of a new species of Microglanis, with a review of the status of Microglanis cibelae (Siluriformes: Pseudopimelodidae)

In a recent study based on the generalized mixed Yule coalescent method for delimiting species, a threshold of 2% genetic distance using cytochrome c oxidase subunit I sequences was used to delimit the species of Microglanis. That action resulted in assembling several populations of Microglanis from Atlantic coastal rivers between Rio Grande do Sul and São Paulo states as a single species, Microglanis cottoides, including Microglanis cibelae as a junior synonym. We reexamined these populations and found three species diagnosed by their morphology and that constitute separate mtDNA lineages, including a new species. The synonym of M. cibelae and M. cottoides is reviewed and refuted based on morphological and molecular evidence. M. cibelae and the new species are sympatric and occasionally syntopic in the Tramandaí, Mampituba, and Araranguá river basins. The new species is distinguished from M. cibelae and M. cottoides by the anterior margin of the posttemporosupracleitrum narrow articulated with the epioccipital, the short mental and maxillary barbels, and depressed head and body.

Archolaemus janeae (Gymnotiformes, Teleostei): First insights into karyotype and repetitive DNA distribution in two populations of the Amazon

Archolaemus, one of the five genera of Neotropical freshwater fish of the family Sternopygidae (Gymnotiformes), was long considered a monotypic genus represented by Archolaemus blax. Currently, it consists of six species, most of them occurring in the Amazon region. There are no cytogenetic data for species of this genus. In the present study, we used classical cytogenetics (conventional staining and C-banding) and molecular cytogenetics (probes of telomeric sequences and multigenic families 18S rDNA, 5S rDNA, and U2 snDNA) to study the karyotype of Archolaemus janeae from Xingu and Tapajós rivers in the state of Pará (Brazil). The results showed that the two populations have identical karyotypes with 46 chromosomes: four submetacentric and 42 acrocentric (2n = 46; 4m/sm + 42a). Constitutive heterochromatin occurs in the centromeric region of all chromosomes, in addition to small bands in the interstitial and distal regions of some pairs. The 18S rDNA occurs in the distal region of the short arm of pair 2; the 5S rDNA occurs in five chromosome pairs; and the U2 snDNA sequence occurs in chromosome pairs 3, 6, and 13. No interstitial telomeric sequence was observed. These results show karyotypic similarity between the studied populations suggesting the existence of a single species and are of great importance as a reference for future cytotaxonomic studies of the genus.

Gymnotus paraguensis, a Good Example of Phenotypic Plasticity in the Pantanal Biome, Brazil

Gymnotus is the most studied genus of the order Gymnotiformes, but the morphological similarities of the different species make it difficult to identify taxa reliably. The present study is a continuation of the ongoing research into the taxonomic diversity of the stocks of Gymnotus sold as live bait in the Pantanal, Brazil. These studies have been based on cytogenetic analyses, DNA barcoding, and the analysis of coloration patterns. The results of the cytogenetic analysis confirmed the presence of three distinct strains, recognized as Gymnotus paraguensis, G. sylvius, and G. pantanal. However, the results revealed that the molecular operational taxonomic units identified as G. paraguensis actually include a relatively diverse set of fish, separated by considerable genetic distances. As the G. paraguensis specimens also presented considerable variation in coloration patterns, further genetic diversity analyses were conducted on these individuals, to test the hypothesis that more than one species is present in this cytotaxonomic unit. The haplotype network revealed a regional pattern in the distribution of this species. The results indicate that the observed variation in coloration patterns is associated with a high degree of phenotypic plasticity in G. paraguensis. These findings emphasize the importance of using an integrative approach for a more accurate diagnosis of Gymnotus, in particular, the species marketed as live bait for the fisheries of the upper Paraguay River basin in the Brazilian Pantanal.

Diversification of Neotropical Freshwater Fishes

Neotropical freshwater fishes (NFFs) constitute the most diverse continental vertebrate fauna on Earth, with more than 6,200 named species compressed into an aquatic footprint <0.5% of the total regional land-surface area and representing the greatest phenotypic disparity and functional diversity of any continental ichthyofauna. Data from the fossil record and time-calibrated molecular phylogenies indicate that most higher taxa (e.g., genera, families) diversified relatively continuously through the Cenozoic, across broad geographic ranges of the South American platform. Biodiversity data for most NFF clades support a model of continental radiation rather than adaptive radiation, in which speciation occurs mainly in allopatry, and speciation and adaptation are largely decoupled. These radiations occurred under the perennial influence of river capture and sea-level oscillations, which episodically fragmented and merged portions of adjacent river networks. The future of the NFF fauna into the Anthropocene is uncertain, facing numerous threats at local, regional, and continental scales.