Uruguay River Basin Research Articles

The Uruguay River: A Permeable Border in South America

The Uruguay River basin in South America has held a social, cultural, environmental, and economic relevance for many centuries. The river flows for about 2,000 km, linked to an important remnant of native forest, the Selva Misionera in Argentina, and to a Brazilian conservation unit for biodiversity, the Turvo State Park. The Uruguay River is fed by several other important rivers, forming a basin region in which thousands of people live and work. The history of the Uruguay River is intensively linked to the permeable borders between Brazil, Argentina, and Uruguay where different social groups circulated in diverse historical time periods. Forests along the river played a very important role with emphasis on the extraction and trade of yerba mate (Ilex paraguariensis, Saint-Hilaire), a forest product widely consumed in southern America, and also the timber extraction from native forests, during the nineteenth and twentieth centuries. As a result, a profound socio-environmental transformation took place with the reconstruction of regional landscapes shaped by the Uruguay River basin.

Spatio-temporal distribution of preimaginal black flies (Diptera: Simuliidae) in streams of a sub-basin of the Uruguay river basin, southern Brazil

Adult females of most black flies species (Diptera, Simuliidae) exhibit a blood-sucking habit. Immature stages develop in water courses and are important in the ecology of lotic environments. We aim to understand the distribution of immature simuliids in the hydrographic sub-basin of the Comandaí river, in Northwest of Rio Grande do Sul, Brazil. For that purpose, simuliids were sampled in three stretches (source, intermediate and mouth) of nine streams, distributed along the three main regions of the sub-basin. Evaluations of the influence of abiotic factors in different spatial and temporal scales were made. Sampling was carried out in two seasons: between September and November 2016 (spring), and between April and July 2017 (autumn). In total, 17,146 individuals were sampled (larvae of last instars and pupae), which resulted in the identification of eleven Simuliidae species. The most abundant species were Simulium pertinax Kollar (77.55%), followed by Simulium incrustatum Lutz (14.56%) and Simulium subpallidum Lutz (2.35%). Regarding the identification of indicator species, S. pertinax, Simulium jujuyense Paterson & Shannon, S. subpallidum and Simulium orbitale Lutz stood out in mouth stretches, and Simulium rubrithorax Lutz in source stretches. Environmental variables such as conductivity, altitude, canopy cover and stream width were interpreted as important conditioning factors for the distribution of simuliid immature stages. In general, we concluded that Simuliidae are more abundant during spring in the study area, mainly downstream. This information may contribute to the implementation of efficient measures to control species of health importance in southern Brazil.

Spatial population structure: patterns of adaptation in populations of the water hyacinth grasshopper Cornops aquaticum (Bruner 1906)

AbstractThe water hyacinth grasshopper Cornops aquaticum (Bruner 1906) constitutes an appropriate model to assess phenotypic and karyotypic variability in the context of differentiation and adaptation of insect populations because it occurs over a wide latitudinal range. This study represents a general analysis of phenotype, karyotype and molecular variation in native populations of C. aquaticum in South America. This is also relevant because this insect is considered a promising biological control agent of water hyacinth, a native South American aquatic plant but a pest in South Africa. Along Paraná and Uruguay River Basins, body size correlated negatively with latitude, and positively so with temperature and rainfall in both sexes. To test whether the chromosomal and phenotypic patterns were adaptive, we compared them with neutral microsatellite loci variation in populations from the medium and lower course of the Paraná River. Firstly, the lack of pairwise association between karyotype and phenotype distance matrixes with that of neutral loci suggested non-neutrality. Secondly, phenotypic differentiation for all morphometric traits (PST) was significantly larger than molecular differentiation (FST), indicating a prevailing divergence selection effect on the observed phenotypic patterns. Finally, the phenotypic and genotypic spatial structures – inferred from Bayesian approaches – were discordant: neutral genetic structure clustered together most populations except for the two southernmost, downstream ones, whereas phenotypic spatial structure groups together all the deltaic populations and singles out the two northernmost ones. The results suggest directional selection leading to higher centric fusion frequencies in the downstream populations and favouring morphometric optimal differences in relation to the environment.

Quaternary formations mapping in the region of Volta Grande do Rio Uruguai (Brazil)

Quaternary formations (detrital and weathered materials) are an important natural resource for different areas of scientific investigation, from understanding their relation to erosive processes and morphodynamic processes that create landforms or to understanding the history of the first human settlements (geoarcheology). Quaternary coverings can be formed in situ or be transported by external geologic agents. Regarding soils, Quaternary formations are related to landscape topography and are transformed according to the characteristics of this topography. Hence, classifying and mapping these soils is not always easy. The present article aims to map the Quaternary formations along a stretch of the Uruguay River basin known as Volta Grande (SC/RS-Brazil), by using topographic attributes derived from the SRTM GL1-Up Sampled digital elevation model, soil particle-size analysis, and a generated Multiresolution Index of Valley Bottom Flatness (MRVBF) index . The results of the analysis show that: (i) colluvium is the predominant Quaternary formation in the study area; (ii) there is a predominance of clay, corroborating previous studies of the region; (iii) the spatial distribution of the study area’s Quaternary formations reflect local slope dynamics based on morphology and topographic position; and, (iv) the existence of colluvium-alluvium on the Uruguay River’s banks indicates that slope attributes contributed to the pedogeomorphological dynamics of the study area and not only fluvial dynamics. Based on the results, the methodology applied in this study might be useful for pedogeomorphological studies, notably in the analysis and mapping of Quaternary formations, despite some of its limitations.

ANÁLISE MORFOMÉTRICA DO RELEVO DA REGIÃO HIDROGRÁFICA DA VÁRZEA – ALTO RIO URUGUAI (RS)

Este trabalho apresenta resultados relativos à análise e interpretação de dados morfométricos e observacionais da região hidrográfica do rio da Várzea – norte do Estado do Rio Grande do Sul –, no contexto da alta bacia do rio Uruguai. O objetivo foi avaliar se os índices morfométricos analisados são indicativos ou não de maturidade do relevo e de influência tectônica na região. A metodologia utilizada baseia-se em uma abordagem morfoestrutural por meio de análise de perfis longitudinais de canal e topográficos de varredura, de parâmetros morfométricos e de superfícies de isobase. Dentre os principais resultados apontados destacam-se: (i) curvas hipsométricas predominantemente convexas e representativas de uma morfologia que passa por ativa desnudação; (ii) uma onda erosiva remontante na direção sul da região hidrográfica que amplia a desnudação dos planaltos superiores (Planalto das Missões e dos Campos Gerais); (iii) a elaboração das escarpas erosivas, a incisão dos vales e a elaboração da superfície do Planalto Dissecado do rio Uruguai onde se concentram os maiores declives; (iv) na contraposição ao mapeamento geomorfológico da região constatou-se a coincidência das compressões de isolinhas (anomalias topográficas) com os limites entre os compartimentos planálticos da região. A morfogênese desse relevo é coerente com a atuação de fatores estruturais de caráter tectônico que fizeram com que houvesse um encaixamento do rio Uruguai produzindo uma onda erosiva remontante que se expressa na rede de drenagem.
 Palavras-chave: morfologia estrutural, perfil longitudinal de canal, dissecação fluvial

The Impact of Regional Climate Change on Hydroelectric Resources in South America

The objective of this study is to estimate the impact of climate change on the hydroelectric potential of various basins across South America. Three different downscaled global climate models are used to estimate the percentage changes in rainfall and streamflow by the 2030s and 2080s under a high emission scenario in comparison to 1961–1990 baseline data. While rainfall is projected to increase slightly over the Uruguay River basin, rainfall over the Amazon and Brazil’s Northeast region is expected to decline. As a consequence of climate change, streamflow in the São Francisco River, Tocantins River and Parnaiba River is projected to decline 46%, 31% and 26%, respectively in the coming 3 decades compared to data from 1961 to 1990. Furthermore, the increasing demands for water from the São Francisco River could become greater than available streamflow by the 2030s. Additionally, one of the three climate models indicated that the São Francisco and Parnaiba Rivers’ streamflow and hydroelectric production could potentially cease in the second half of the 21st century. Despite some inconsistencies between the long term projections from the 3 different climate models, the results of this research are important in the context of regional climate change, agricultural and energy resource planning.

Limnoperna fortunei - Updating the geographic distribution in the Brazilian watersheds and mapping the regional occurrence in the Upper Uruguay River basin

Abstract: Limnoperna fortunei is an invasive alien species (IAS) that cause serious ecological and economic problems in Brazilian freshwater environments. Due to its high dispersion capacity and the lack of new records in peer-reviewed journals we carried out an extensive survey to update the distribution of L. fortunei in the Brazilian hydrographic basins. We also performed a detailed investigation of its distribution in the Upper Uruguay River basin using a molecular method. We presented new records, showing the invasion in new basins and a wide distribution in the basins previously infested. Additionally, we confirmed that the Upper Uruguay River is fully colonized by the golden mussel, being distributed in the lentic, lotic, and transitional lotic/lentic environments presented in this region. This update is an important tool for the implementation of guidelines and the development of safety protocols and sanitary barriers to avoid the dispersion of this IAS to new environments..

Interdisciplinary research networks and science-policy-society interactions in the Uruguay River Basin

The Uruguay River Basin (URB) that extends along Argentina, Brazil and Uruguay has been the hub of increasing pressures caused by the expansion of industrial agriculture, forestry and infrastructure projects in hydroenergy and transportation. There are growing concerns that the fragmented institutional framework is inadequate to address the growing challenges. Interdisciplinary research networks can contribute to creating perspectives of the basin that are policy and governance relevant. In this paper, we set out to interrogate the potential scope of interdisciplinary research networks (IRNs) for the advancement of basin governance framework for the URB. We envision IRNs as knowledge actors that can open up opportunities to mediate and connect basin actors across different spaces – academic, policy, technical-administrative and social. We highlight a series of pathways to advance networks actions in creating opportunities to fill the gaps of transboundary basin governance, and acknowledge the challenges associated with doing this work in the URB and other basins around the world.

Iterative taxonomic study of Pareiorhaphis hystrix (Siluriformes, Loricariidae) suggests a single, yet phenotypically variable, species in south Brazil.

Pareiorhaphis hystrix is a widely distributed species, occurring in the upper and middle Uruguay River and in the Taquari River basin, Patos Lagoon system, southern Brazil. Morphological variation has been detected throughout the distribution of P. hystrix, and this work seeks to test the conspecific nature of populations in several occurrence areas. Specimens from six areas in the Uruguay River basin and three in the Taquari River basin were compared. Variance analysis (ANOVA) was performed for the meristic data, and Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) were conducted for morphometric data. Molecular analyses used coI, cytb, 12S and 16S mitochondrial genes, examining nucleotide diversity, haplotype diversity, genetic distance, and delimitation of possible multiple species through the Generalized Mixed Yule Coalescent (GMYC) method. Phylogenetic relationships of studied populations were also investigated through Bayesian inference. While PCA indicated a tendency of overlap between areas, ANOVA and LDA detected a subtle differentiation between populations from the two hydrographic basins. Yet, both latter analyses recovered the population from Pelotas River, a tributary to Uruguay River, as more similar to populations from Taquari River, which is congruent to morphological observations of anterior abdominal plates. The molecular data indicated a nucleotide diversity lower than the haplotypic diversity, suggestive of recent expansion. The concatenated haplotype network points to slight differentiation between areas, with each locality presenting unique and non-shared haplotypes, although with few mutational steps in general. The species delimitation by coalescence analysis suggested the presence of a variable number of OTUs depending on the inclusion or exclusion of an outgroup. In general, the morphological data suggest a subtle variation by river basin, while the genetic data indicates a weak population structuration by hydrographic areas, especially the Chapecó and Passo Fundo rivers. However, there is still not enough differentiation between the specimens to suggest multiple species. The iterative analyses indicate that Pareiorhaphis hystrix is composed of a single, although variable, species.

Evolutionary biogeography of the freshwater fish family Anablepidae (Teleostei: Cyprinodontiformes), a marine-derived Neotropical lineage

Cladistic biogeography is an evolutionary biogeographic approach that infers area relationships by comparing area cladograms derived from different phylogenetic hypotheses. The South American freshwater ichthyofauna is enriched by an extraordinary number of marine-derived lineages, presenting its own phylogenetic and biogeographic patterns. Here, we performed a Brooks Parsimony Analysis (BPA) with the latest phylogenetic proposals for Anablepidae to compare hypotheses about the historical relationships among areas previously recognized based on fish species from the Neotropical region. We found that the area relationships for Anablepidae are in accordance with the pattern evidenced for other marine-derived lineages. The general area cladogram obtained shows a three-area relationship pattern, where freshwater is the sister group of Pacific + Atlantic marine areas. Within the freshwater clade, Southern Brazil + Uruguay River basin and Northwestern Argentina + Midwestern Argentina form two clades. Vicariance, dispersal, and extinction events related to Miocene and Quaternary marine transgressions and ancient connections between the Iguacu and Upper Uruguay River basins supported the historical relationships among areas proposed here. Our results may be applied to patterns shown by other marine-derived lineages, as well as other freshwater organisms not necessarily having marine origins.

Estructura de la comunidad íctica del arroyo Paraíso afluente del río Uruguay. Misiones. Argentina

Se determinó la composición, diversidad específica, abundancia, número de endemismos y estructura trófica de la comunidad íctica del arroyo Paraíso, afluente del río Uruguay. Se realizaron cuatro campañas de pesca experimental entre setiembre de 2013 y marzo de 2015, utilizando ocho redes de espera monofilamento. La captura total fue de 217 individuos pertenecientes a 35 especies de las cuales el 77% corresponde a los órdenes Characiformes (16 especies) y Siluriformes (11 especies) y el 33% a los órdenes Cichliformes (siete especies) y Gymnotiformes (una especie). La diversidad alfa de número efectivo fue de 16,44. De acuerdo con el estimador no paramétrico Chao 1, el inventario de peces es incompleto, restarían encontrar al menos 16 especies. Las especies raras o accidentales representaron el 66%, con abundancia relativa inferior al 10%. Las especies comunes fueron Crenicichla missioneira, Leporinus amae, Leporinus striatus y Astyanax lacustris. Se registraron siete especies endémicas de la cuenca del río Uruguay: C. missioneira, C. celidochilus, C. tendybaguassu, L. amae, Astyanax paris, A. troya, y Hemiancistrus fulliginosus. La mayoría de las especies capturadas (83%) fueron de pequeño porte. El índice de dominancia comunitaria fue máximo en primavera (0,81). La materia orgánica de origen alóctono fue el principal recurso alimentario. Se reconocieron seis grupos tróficos y el 61,5% de las especies perteneció al grupo de los detritívoros u omnívoros. La comunidad presentó actividad reproductiva durante todas las estaciones del año, con preponderancia en la primavera y el invierno con especies como L. striatus y A. piracicabae. La elevada diversidad específica, el endemismo y la alta dependencia del material orgánico alóctono de la ictiofauna demanda la urgente necesidad de protección y conservación de este curso de agua.

Tree community patterns along pond-upland topographic gradients, upper Uruguay River basin, southern Brazil

We investigated the interrelations between environmental variables (proxies for water availability and soil physico-chemical properties) and tree community patterns (diversity, composition and structure) along pond-upland topographic gradients within depressional watersheds in the upper Uruguay River basin in southern Brazil. Sampling plots were allocated in four topographic habitats: (1) inside ponds (wetland sites) and (2) immediately outside them, and in areas with (3) 60 cm and (4) 120 cm of elevation in relation to their limits (upland sites). Environmental conditions and forest composition varied along pond-upland gradients, but the diversity and structure of tree communities did not. Species turnover was associated with changes in topography-driven environmental conditions, notably water availability. Depressional watersheds show regionally unique abiotic and biotic features but are virtually unprotected by Brazilian private land legislation.

Evaluating the role of predatory fish controlling the invasion of the Asian golden mussel Limnoperna fortunei in a subtropical river

Abstract The invasive Asian golden mussel Limnoperna fortunei is continuously expanding through South America, altering aquatic ecosystem structure and functioning. While several native fish species predate on this mussel, these interactions, and their consequences for the food web, have not been studied in depth. We combine a survey of the fish assemblage trophic structure using gut contents and stable isotope analysis with an in situ exclusion experiment in order to: (a) determine the main fish species predating on L. fortunei; (b) estimate the contribution of L. fortunei to the biomass of fish assemblage; and (c) evaluate the role of fish on the density and maximum shell length of L. fortunei in the lower Uruguay River (the Río de La Plata Basin). We found that about one third of fish species in the assemblage (28 out of 81 species) consumed L. fortunei, which was an important food item (>10% of the dietary volume and >30% of frequency of occurrence) for 11 fish species. Stable isotope mixing models consistently suggested that >14% of the total biomass of the fish assemblage was derived directly from carbon derived from L. fortunei tissues. In addition, the exclusion experiment demonstrated that fish predation reduces the mussel density by c. 70% and the mussel maximum shell length by c. 40%. Synthesis and applications. Our research suggests a top‐down effect of fish on the invasive Asian golden mussel's abundance. This work highlights the need to preserve the native fish communities, particularly in South America, where many vulnerable migratory fish are of key relevance as Limnoperna fortunei consumers. In the light of these findings, actions such as implementing efficient fish passage technologies in the actual (and projected) dams of the Uruguay River basin and elsewhere become essential to avoid local extinctions of these natural invasion controls upstream of the dams.

Length‐weight relationship of 13 middle Uruguay River basin species, Southern Brazil

Length-weight relationship (LWRs) were determined for 13 fish species from the Uruguay River. The fish were caught in six locations and sampled at each location during each season, totaling 72 samplings, starting in May 2016 and ending in February 2018. Various materials were used such as gillnets (15; 20; 25 30; 40 and 80 mm, triple mesh 150.30.150 150.40.150 and 150.50.150 mm, 8 mm trawl). We also used two longlines, 100 m long, 30 hooks each (hooks 5/0 and 12/0), baited with small fish, corn and snail. Length-weight relationship were adjusted appropriately for all species (r2 > .95). The b values of the LRW equations ranged from 2.38 in Steindachnerina brevipinna to 3.62 in Pimelodus atrobrunneus.

Detection of natural hybridization and delimitation of two closely related operational taxonomic units of the Astyanax fasciatus (Teleostei: Characidae) complex through integrative approaches

Abstract Astyanax is a species-rich, non-monophyletic genus composed of several supraspecific taxa that are poorly delimited. The Astyanax fasciatus complex is one of these taxa and shows high taxonomic complexity. To elucidate the evolutionary history of the A. fasciatus complex from southern South America, we conducted cytogenetic, molecular and morphological analyses in specimens from the Uruguay River basin. Cytogenetic characters demonstrated two closely related operational taxonomic units: Astyanax sp. 1 (8m+22sm+10st+6a), Astyanax sp. 2 (8m+24sm+10st+4a) and natural hybrids (8m+23sm+8st+5a). 5S ribosomal DNA sites were found in two pairs of m chromosomes and one pair of a chromosomes in Astyanax sp. 1, two pairs of a chromosomes and one pair of m chromosomes in Astyanax sp. 2, and three m chromosomes and three a chromosomes in hybrids. As51 sites were found in three chromosomes in Astyanax sp. 1 and in five chromosomes in Astyanax sp. 2 and hybrids. Mitochondrial sequence analyses did not separate the two units and hybrids. Morphological analyses revealed differences between Astyanax sp. 2 and hybrids. This secondary contact with gene flow between lineages that diverged long ago might slow or reverse the differentiation/speciation process. These results help us to understand the evolutionary history of this highly complex clade of Astyanax in southern South America.

Fishes community composition and patterns of species distribution in Neotropical streams

Abstract: The ichthyofauna of streams in the Neotropical region is not yet fully known. This study aims to investigate the ichthyofauna composition of six streams of the Ijuí River sub-basin, Rio Grande do Sul State, inserted in the Uruguay River basin, as to contribute to the knowledge of fishes species richness and distribution in the south of Brazil. Sampling was carried out between July 2015 and May 2016, bimonthly, using the technique of electric fishing to collect the fishes. Spatial variations (per sampled stream) in the ichthyofauna composition were tested with a permutational multivariate analysis of variance. In total, we collected 5,029 individuals from 55 species, 13 families and five orders. From these species, 17 are endemic to the Uruguay River basin. Five species alone represented approximately 70% of the ichthyofauna abundance sampled. Our hypothesis that the fish community composition is not homogeneous along the streams sampled was confirmed and we observed that species complexity increases from the upstream closest area to the downstream according to the river continuum concept.

First record of microplastics in two freshwater fish species (Iheringhthys labrosus and Astyanax lacustris) from the middle section of the Uruguay River, Brazil

Abstract Aim The aim was to analyze the incidence of microplastics in the diet of fish in the middle Uruguay River. Methods The present work analyzed the gastrointestinal content of two species: Astyanax lacustris and Iheringichthys labrosus. Results This study provides the first evidence of synthetic materials, such as fibres and plastics in the gastrointestinal tract of fish species in the Middle Uruguay River basin. A sample of sixty-one A. lacustris and twenty-nine I. labrosus were examined to highlight the ingestion of microplastics in the middle section of the Uruguay River in Brazil. In the A. lacustris, eleven fibres and two fragments were found in their gastrointestinal contents, corresponding to 18.1% of the specimens, while in the I. labrosus, twelve fibres and one fragment were found, corresponding to 34.5% of the specimens analyzed. Blue staining was also prevalent in the occurrence of microplastics. Conclusions These data are the first record of microplastics in this zone and represent a baseline for this contamination for future studies.

Genetic evidence supports polygamous mating system in a wild population of Prochilodus lineatus (Characiformes: Prochilodontidae), a Neotropical shoal spawner fish

ABSTRACT Behavioral observations made on fish have revealed remarkably diverse reproductive strategies, including polygamy by both sexes. Still, to date, most Neotropical species remain unstudied as to whether the observed reproductive behavior in natural populations correlates with their genetic mating systems. Here, we investigated the genetic mating system of a wild population of Prochilodus lineatus settled in the Middle Uruguay River basin. By using sibship reconstruction and parental inference methods based on microsatellites’ genotypes, we inferred 45 females and 47 males as potential parents of the 87 larvae analyzed. We found evidence supporting polygamous mating in both sexes: while a high percentage of males (44.7%) fertilized the eggs of one female, 55.3% of the inferred males fertilized eggs of up to four females. Likewise, while 44.5% of the inferred females had their eggs fertilized by one only male, 55.5% of females were fertilized by multiple males. The estimated proxy of the effective population size (Nb) was 126, exhibiting moderate to high levels of genetic diversity. The genetic evidence contributed in this study complements earlier behavioral observations of formation of spawning nuclei of aggregating breeders, which may be promoting a polygamous mating strategy in this long-distance migratory fish.

LISTA DE ESPECIES DE PECES DE LA CUENCA DEL RÍO QUEGUAY, RÍO URUGUAY BAJO

The Queguay river is one of the main tributaries of the lower Uruguay river basin. At the confluencce of its main effluents large wetlands and riparian forest are developed, that according to their biodiversity and ecosystem functions have been included in the National Protected Areas System, under the name “Montes del Queguay”. At a national scale the basin is included in two ecoregions: the Basaltic Slope and the Western Sedimentary Basin. Except for an unsupported listing in scientific collections, there is no documented information about its ichthyofauna. Therefore, the objective of this work was to prepare an updated list of the fish species in the Queguay River basin. Considering all the sources of information, a total of 94 species were registered for the basin, corresponding to 60 genera, 28 families and nine orders. The composition of species found was similar to the largest tributary of the low Uruguay ecoregion, the Rio Negro basin. The main migratory species of the Plata basin stand out, as well as a species of annual fish endemic to the wetlands of the basin, and the presence of an invasive exotic species (Cyprinus carpio).

A new species of Imparfinis Eigenmann & Norris, 1900 (Siluriformes: Heptapteridae) from the Tapajós basin, Brazil.

Imparfinis comprises 20 valid species in the Heptapteridae, being the most diverse taxonomic group of catfishes of the Nemuroglanis subclade. The genus has one of the widest geographical distributions in the neotropical region, found on both sides of the Andes, from Costa Rica to the Paraná and Uruguay river basins in Argentina. A new species of Imparfinis is described from streams of the upper Rio Tapajós and its tributary Teles Pires in northern Brazil. The new species is diagnosed from all congeners by the presence of a vertical dark brown band W-shaped at the base of the caudal-fin rays, a thick dark brown lateral stripe from the snout to the end of the caudal peduncle, dark brown head, long maxillary barbel surpassing the distal margin of the pectoral fin, and presence of 39 or 40 total vertebrae.