Abstract Farfantepenaeus brasiliensis (Latreille, 1817) and Farfantepenaeus paulensis (Pérez Farfante, 1967), commonly known as pink shrimps, are two commercially important penaeid species caught by artisanal and industrial fisheries in the Southwestern Atlantic Ocean. The currently known southern distribution for F. brasiliensis extends to Rio Grande do Sul (Brazil), while F. paulensis reaches the coastal waters of Buenos Aires (Argentina), although Uruguay represents the southern limit of commercial captures for the latter. In the shrimp season of 2019 (February-May) the presence of F. brasiliensis was recorded together with F. paulensis in the brackish coastal lagoons of Uruguay (34º30’ to 34º50’S). A total of 143 specimens of F. brasiliensis and 152 of F. paulensis were analyzed evaluating morphological, morphometric and genetic differences. The presence of both species was validated based on morphological differences and sequencing the Cytochrome Oxidase I (COI) mitochondrial gene. Significant morphometric differences were found between both species, particularly, the larger rostral length in relation to the carapace and cephalothorax length in F. paulensis compared to F. brasiliensis. To our knowledge, this is the first confirmed record and commercial catch of F. brasiliensis in Uruguayan waters. This southwards expansion could be explained by extending climatic variability events associated with prolonged periods of positive sea surface temperature anomalies in the region. Given the potential commercial relevance of the species, a better understanding of the southward expansion of F. brasiliensis into Uruguayan waters would be helpful in developing efficient management and conservation strategies under a scenario of increasing water temperatures.

ABSTRACT The La Plata River basin, the second largest drainage basin in South America, supports important fisheries, in which the sábalo Prochilodus lineatus is the leading species measured as extracted volumes. To characterize the population structure of the sábalo in the middle and lower regions of the La Plata River basin, cytochrome b DNA sequences of 121 samples collected in La Plata, Paraná and Uruguay rivers were used. Results suggest the presence of at least two populations: one that we called “southern population” uses the La Plata River and the lower sections of the Paraná and Uruguay rivers and another population (called here “northern population”) in the middle section of the Uruguay and Paraná rivers. The southern population would have a larger effective population size and coalescence-based analyses reveal an asymmetric gene flow, mainly from north to south. A striking result is that samples from the middle sections of the Paraná and Uruguay rivers are more alike to each other than they are to the other samples of their respective rivers. This similarity could be explained by historical reasons, probably as a consequence of the proximity that both rivers had until 100,000 years ago. The presence of different management units being exploited by the continental fisheries of three countries demands coordination at a regional level in order to maintain a sustainable fishery.

Six species of Trifolium (T. polymorphum Poir., T. riograndense Burkart, T. argentinense Speg., T. medium L., T. pratense L. and T. repens L.) were analyzed using inter-simple sequence repeats (ISSR) markers. Six selected primers generated 186 polymerase chain reaction (PCR) products exploring 112 loci in 34 genotypes analyzed with molecular sizes ranging from 200 to 1300 bp. These primers were able to discriminate among and within species, with the PCR products being on average 41.6% species-specific and 59.9% polymorphic at the within species level. Nuclear DNA content was determined by flow cytometry and revealed variation among species. The 1Cx genome size values were calculated and were found to range from 0.46 pg (T. pratense) to 0.96 pg (T. polymorphum). Genome size values of South American species were higher than those of Eurasiatic origin. The analyses of the molecular data grouped the six species in agreement with their geographical origin and clearly differentiate T. polymorphum from T. argentinense. The Eurasiatic group showed the highest average of species-specific bands (45.3%) and the South American group exhibited the highest amount of total bands (59.7). The highest level of intra-species polymorphisms was detected in T. argentinense (92.9%), followed by T. medium (89.5%).