DNA barcoding identifies three species of croakers (Pisces, Sciaenidae) in the ichthyoplankton of the High Paraná River.

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.

Molecular and morphological evidence revalidates Acrobrycontarijae (Characiformes, Characidae) and shows hidden diversity.

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.

Processes that drive the population structuring of Jenynsia lineata (Cyprinidontiformes, Anablepidae) in the La Plata Basin.

The distribution of genetic diversity across a species distribution range is rarely homogeneous, as the genetic structure among populations is related to the degree of isolation among them, such as isolation by distance, isolation by barrier, and isolation by environment. Jenynsia lineata is a small viviparous fish that inhabits a wide range of habitats in South America. To decipher the isolation processes that drive population structuring in J. lineata, we analyzed 221 sequences of the mitochondrial cytochrome c oxidase I gene (COI), from 19 localities. Then, we examined the influence of the three most common types of isolation in order to explain the genetic variation found in this species.Our results revealed a marked structuration, with three groups: (a) La Plata/Desaguadero Rivers (sampling sites across Argentina, Uruguay, and Southern Brazil), (b) Central Argentina, and (c) Northern Argentina. A distance-based redundancy analysis, including the explanatory variables geographical distances, altitude, latitude, and basin, was able to explain up to 65% of the genetic structure. A variance partitioning analysis showed that the two most important variables underlying the structuration in J. lineata were altitude (isolation by environment) and type of basin (isolation by barrier).Our results show that in this species, the processes of population diversification are complex and are not limited to a single mechanism. The processes that play a prominent role in this study could explain the high rate of diversity that characterizes freshwater fish species. And these processes in turn are the basis for possible speciation events.