RESUMO
We conducted a revision of the Neotropical genus Acrobrycon. A previous study synonymized the species, A.ipanquianus, distributed from the western portion of the Amazon River to the north-western region of the La Plata River Basin, and A.tarijae, with type locality in the Lipeo River in Bolivia. We revisited this result by collecting new morphometric, meristic, and genetic data (COI mitochondrial gene) for 24 individuals distributed along La Plata River Basin in Argentina, and discussed our results in the context of multiple biogeographic processes of isolation in that basin. Our results revealed a more complex history of diversification and geographic distribution across Acrobrycon species than previously suspected, probably associated with multiple biogeographic processes of isolation in La Plata River Basin. We present new evidence that led us to reconsider the validity of A.tarijae, which is distinguishable from A.ipanquianus by the number of vertebrae (37-39 vs. 41-42) and pleural ribs (12-13 vs. 14). These results were also supported by our molecular analyses that revealed a genetic divergence >4% between A.ipanquianus and A.tarijae. We also identified two main genetic clusters within A.tarijae: the first cluster consisted of specimens from the Bermejo, Pilcomayo, Itiyuro and Juramento river basins (northern Argentina); and the second cluster included specimens from the southernmost basins, such as the Salí River in Tucumán, Cuarto River in the province of Cordoba and the Quinto River in the province of San Luis. Our results suggest that the genetic structure observed in A.tarijae is the result of the type of drainage (endorheic vs. exorheic) and geographical distance.
RESUMO
In the province of Misiones (Argentina), the filling of the Yacyretá Reservoir (Argentina-Paraguay) to its final dimensions in 2011 formed new aquatic ecosystem, e.g., Garupá Stream was converted into a subreservoir. Reports have been made in this stream of adult individuals and spawning of the Family Sciaenidae, excellent colonizers of modified environments. The larvae of this family are morphologically similar, particularly among Pachyurus and Plagioscion species, making taxonomic differentiation difficult. In the present work, sciaenidae larvae were characterized molecularly at the cytochrome c oxidase subunit I gene in order to determine which species use this environment for reproduction. Additionally, genetic distances, Barcode Index Number (BIN) and Automatic Barcode Gap Discovery method (ABGD) were estimated and phylogenetic trees were reconstructed. The results indicated the presence of Plagioscion ternetzi and Pachyurus bonariensis larvae, and for the first time in tributaries of the region, Plagioscion squamosissimus. The incorporation of P. bonariensis and P. squamosissimus to the faunistic assemblage of ichthyoplankton in the Garupá Stream supports better characterization of the species richness of this secondary watercourse modified by the Yacyretá Reservoir, and advancement in our understanding of use of this area for reproduction.