A panbiogeographical model to prioritize areas for conservation along large rivers

Aim The large rivers of the Neotropics are considered areas of high diversity and endemism, which play an important role in the distribution patterns and evolution of Neotropical biota. Several methods have been proposed for prioritizing terrestrial conservation areas, but there has been little effort to develop models for river systems. We propose a panbiogeographical approach to identify priority areas for conservation along rivers. Location The Plata Basin rivers. Methods We compared the individual tracks (IT) of 96 snake taxa and identified the species associated with rivers using the concept of preferential direction of distribution. For each taxon, we measured the angular deviations between the line of its IT and the course of the rivers on a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with rivers. We detected 35 taxa associated with rivers, and their IT were used to determine the generalized tracks (GT) and nodes. We applied a complementarity algorithm to identify the minimum set of nodes required to represent all species. Results Six nodes were found. The region where the High and Upper Paraná Rivers converge (Node 1) is of first priority, with 60 of 96 species. The second priority is the Lower Paraguay River and northern section of Middle Paraná River (Node 2). The third is the High Paraná, which together with Nodes 1 and 2, comprises 94% of the total species. The fourth and fifth are the High and Middle Uruguay, and the western section of the Upper Paraná and Iberá Marsh system, respectively. These five nodes include all species. Main conclusions Our results highlight the areas of particular interest for the conservation of rivers and provide a biogeographical algorithm for detecting priority conservation areas. The nodes are a biogeographical approach that allows evolutionary and ecological traits to be included in conservation assessment.     

Hidden areas of endemism: Small units in the South-eastern Neotropics

This study aimed to establish if the Lower Río de la Plata Basin (LRPB) wetlands can be considered a biogeographic unit. The species of this area were compiled and segregated according to the habitat, selecting only 87 endemic taxa restricted to the LRPB and linked to wetlands. Distributional data of species obtained from the literature, web databases, biological collections, and field trips were georeferenced. The areas of endemism were established as those areas where the distribution of two or more taxa overlaps in groups of rivers’ sections with geographic continuity and were tested with a cluster analysis. This congruence is due to ecological, geomorphological, and historical factors. Four areas of endemism were found: a broad area that comprises the whole study area (Riverine district), which is divided into three nested smaller areas (Paraguay–Paraná Flooding Valleys, Uruguay Basin, and Paraná Delta subdistricts). Then, we analysed 170 taxa distributions to evaluate the relationship between the study area and the neighbouring biogeographic units. According to the results, the study area belongs to the Paraná biogeographic province. Some areas of endemism are hidden inside broader areas and are hardly detected with the currently used biogeographic grid-methods. We propose to combine the information about ecological requirements of each taxon with its georeferenced records to estimate their areas of distribution as a primary step for searching areas of endemism in intracontinental studies.     

Patterns of population differentiation in annual killifishes from the Paraná–Uruguay–La Plata Basin: the role of vicariance and dispersal

Aim To elucidate the role of vicariance versus dispersal at the microevolutionary scale in annual killifish populations belonging to the Austrolebias bellottii species complex (Rivulidae). Within this complex, A. bellottii and A. apaii have low vagility and occur widely within the study area, making them excellent models for testing biogeographic hypotheses of differentiation. Location South America, in the Paraná–Uruguay–La Plata river basin. Methods Molecular data and morphometric analyses were used to reconstruct the phylogeographic history and morphological variation of 24 populations of two taxa of the A. bellottii species complex. Phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) model‐based methods, estimates of clade divergence times implemented in beast , non‐metric multidimensional scaling, analysis of molecular variance results, and morphological analyses elucidated the role of vicariance versus dispersal hypotheses in population differentiation in the aforementioned river basin. Results In the A. bellottii species complex from the Paraná–Uruguay–La Plata river basin, past allopatric fragmentation from vicariance events seems to be the most plausible scenario for diversification since the Late Miocene and more recently since the Plio‐Pleistocene. The Plio‐Pleistocene vicariance produced the differentiation of three major clades in A. bellottii populations. One clade from the eastern Uruguay River drainage was separated from another in western Uruguay and the Paraná–La Plata River drainages. A later vicariance event split populations to the south (lower Paraná–La Plata Basin) and north (middle Paraná) of the western Paraná River drainage. However, our results do not exclude the possibility of dispersal events among A. bellottii populations from both the Uruguay and Paraná river drainages, which could occur in these river basins during hypothesized connectivity cycles of the Late Pliocene and Pleistocene. Main conclusions Past allopatric fragmentation caused by different vicariance events seems to be the main driver of diversification in the A. bellottii species complex since the Plio‐Pleistocene. However, the current molecular data suggest that populations from both drainages of the Paraná–Uruguay rivers may have experienced cycles of connectivity during the Pleistocene, perhaps including multiple vicariance or dispersal events from populations located in the western lower Uruguay River drainage, which encompassed climatic and geological changes in the Paraná–Uruguay–La Plata Basin.     

Organization patterns of headwater-stream fish communities in the Upper Paraguay–Paraná basins

We compared environmental influences on the assemblages of stream fishes of contiguous but biogeographically distinct parts of the Upper Paraguay and Paraná basins in Brazil, aiming to describe the main distribution patterns of fish species in the headwater streams. We analyzed bimonthly samples in 10 streams in each basin from January to November 2004. Sixty fish species were collected, including 40 species in streams of the Paraguay Basin and 42 species in streams of the Paraná Basin. The species abundance rank did not differ between the basins. We found a clear differentiation between the Paraguay and Paraná stream fish assemblages. There were significant differences in species composition among streams, but no seasonal differences in species composition. Connectivity between streams explains the differences in species composition for the Paraguay streams, but not for the Paraná streams. Hydrological characteristics were the main factors determining species distribution in both basins, suggesting that the migratory capacity of each species and biogeographical barriers may act to filter the local species composition from the total species pool of colonizers. Handling editor: S. M. Thomaz     

A test of the riverine barrier hypothesis in the largest subtropical river basin in the Neotropics

The riverine barrier hypothesis proposes that large rivers represent geographical barriers to gene flow for terrestrial organisms, leading to population differentiation and ultimately allopatric speciation. Here we assess for the first time if the subtropical Paraná–Paraguay River system in the Del Plata basin, second in size among South American drainages, acts as a barrier to gene flow for birds. We analysed the degree of mitochondrial and nuclear genomic differentiation in seven species with known subspecies divided by the Paraná–Paraguay River axis. Only one species showed genetic differentiation concordant with the current river channel, but another five species have an east/west genetic split broadly coincident with the Paraná River's dynamic palaeochannel, suggesting this fluvial axis has had a past role in shaping present‐day genetic structure. Moreover, dating analyses show that these splits have been asynchronous, with species responding differently to the riverine barrier. Comparisons informed by the geological history of the Paraná River and its influence on the ecological and climatic differences among ecoregions in the study area further bolster the finding that responses to this geographical barrier have been species‐specific.     

Siberian and Russian sturgeon natal origin in South America: Fish farm or established population?

Sturgeon (Acipenser baerii and A. gueldenstaedtii) specimens, native to the northern hemisphere, were reported in different environments of the La Plata Basin (South America). The objectives of this study were to provide the first insights into the natal origin and habitat use of these sturgeon species in the La Plata Basin through geochemical analysis (⁸⁷Sr/⁸⁶Sr) of fin spines and to review historical catch reports. Spine core-to-edge ⁸⁷Sr/⁸⁶Sr ratios were measured by LA-MC-ICPMS. A Quadratic Discriminant Analysis model based on water ⁸⁷Sr/⁸⁶Sr baseline of the La Plata Basin was run to infer the natal origin. The isotopic profiles indicate a common origin, compatible with the location of the fish farms in the Uruguay Basin. The A. baerii isotopic time series suggested that the fish moved towards the Paraná Basin months before capture, while A. gueldenstaedtii would have survived a longer time (perhaps years). Seventeen reports of sturgeons were recorded and preserved in museum collections between 1998 and 2020. Sturgeons were collected from Río de la Plata Estuary, Paraná and Uruguay basins and Atlantic coastal lagoons. It is recommended to closely monitor sturgeon catches, paying special attention to the appearance of specimens of reproductive age, in order to generate management and management plans if necessary.     

Abundance and diversity of phytoplankton in the Paraná River (Argentina) 220 km downstream of the Yacyretá reservoir.

Patterns in the temporal composition, abundance and diversity of the phytoplankton community of the Paraná river prior to and after the initial filling phase of the Yacyretá reservoir are analyzed. The study site is located 220 km downstream from the Yacyretá reservoir and 30 km downstream from the confluence with the Paraguay river. Because both rivers remain separate and unmixed at the study site, we compared the possible effects of the impoundment on both river banks (left and right banks) in hydrological periods with similar duration and magnitude of the low and high water phases. Physical and chemical conditions measured on the right bank (water from the Paraguay river) were similar at both periods (pre and post-impoundment) whereas conductivity, pH and orthophosphate concentration increased on the left bank (water from the High Paraná river and Yacyretá reservoir) after the impoundment. Changes in phytoplankton density and diversity were observed only in samples collected from water flowing from the reservoir (left bank). The density of Chlorophyceae (Chloromonas acidophila, Chlamydomonas leptobasis, Choricystis minor, Chlorella vulgaris, Scenedesmus ecornis, Monoraphidium minutum, M. contortum and M. pusillum) and Cryptophyceae (Rhodomonas minuta, Cryptomonas marssonii and C. ovata) increased while Cyanophyceae (Cylindrospermopsis raciborskii, Raphidiopsis mediterranea and Planktolyngbya subtilis) and Bacillariophyceae (Aulacoseira granulata and its bioforms) decreased compared to previous studies conducted on the left bank of the Paraná river. Phytoplankton collected from the right bank of the river did not differ in pre and post- impoundment samples because they originate from the Paraguay river, which remains relatively unaffected by human activities.     

First observations on longitudinal succession of Zooplankton in the main course of the Paraná River between Santa Fe and Buenos Aires Harbour

The material was been collected in 1972 during a field trip performed by the research vessel of the National Institute of Limnology, Argentina, along the main course of the Paraná River from the Santa Fe harbor down to the Río de la Plata. Sixty sampling stations were covered. In the lower course of the river sampling was carried out in the Paraná Guazú and the Paraná Bravo branches down to its confluence with the Uruguay River, and the Paraná de las Palmas and the Rio de la Plata down to the Buenos Aires harbor. Water samples for chemical analysis were collected and some physical parameters were measured.

Due to the characteristics of the part of the river under consideration, we have divided it into four sectors.

Sixty six species were seen. The rotifers were always the most important. Trichocerca rattus was the predominant species.

The Zooplankton density and specific diversity showing differences between those from industrialized areas and not industrialized ones.     

Karyotype diversity and fish conservation of southern field from South Brazil

Six hundred and twenty-seven specimens of neotropical fishes belonging to thirteen species/populations from southern field (Paraná, State, Brazil) were karyotypicaly analyzed between 2000 and 2006. The study biogeographic region is characterized as a divisor of waters presenting tributaries and headboards of the hydrographic basins of the rivers Tibagi, Iguaçu, Ivaí, and Paranapanema (Upper Paraná Basin) and Ribeira river (East Basin). Two patterns of karyotypic diversification were verified, being one more conserved in the karyotypic macrostructure and the other more diversified. The understanding at of this variability with views to the citotaxonomy and biological conservation was interpreted at the light of (1) the historical biogeography, (2) of the evolutionary time, and (3) of the biology of the species, indicating the study area as highly relevant for the selection of evolutionary potential.     

On the spread of the Russian sturgeon Acipenser gueldenstaedtii (Acipenseriformes: Acipenseridae) in the Neotropics: A marine path to invade freshwater drainages in South America?

Acipenser gueldenstaedtii is a species of sturgeon described from Caspian Sea and Black Sea and their tributaries, occurring in the Eastern Atlantic, Europe and Middle East. This and other two sturgeon species have been accidentally introduced in the Rio Negro, Uruguay, a tributary of the Rio de La Plata. Recently, it has been demonstrated the presence and establishment of A. gueldenstaedtii widespread in the Rio Paraná basin, the largest tributary of the Rio de La Plata, corresponding to the second largest river drainage in the Neotropics. We herein register the presence of the species in the next northern freshwater drainage in South America, representing the first record for Brazil. We further discuss the possibility of dispersal through marine environments to other freshwater drainages in South America through the analysis of its documented occurrence and marine ecoregions in southwestern Atlantic.     

Geographical zonation in the Neotropics of tree species characteristic of the Paraguay-Paraná Basin

Aim This paper uses data from the literature (monographs and taxonomic reviews) to investigate the geographical zonation in South America of 32 common tree species encountered in Paraguay. The actual spatial distribution of the species is then used to provide clues on the plant communities present in the past, and especially during the Wisconsinan age (Last major ice age: 80,000–10,000 bp ). The floristic relatedness between the Paraguayan flora and the neighbouring floras is also investigated. Methods The main vegetation patterns were highlighted using a Discriminant Analysis of the Eigenvectors of Neighbourhood Operator to emphasize the geographical zonation in South America of 32 tree species predominant in the Paraguay‐Paraná Basin. Results Three main vegetation patterns were emphasized: the Chaco, the Paraná‐São Francisco gradient and the Peri‐Amazonian gradient. The Chaco is well defined. The Peri‐Amazonian gradient is characterized by a continuous change in species from the Colombian pole towards the São Francisco pole. The São Francisco gradient shows a continuous change from the São Francisco pole towards the Paraná pole. Some of the species are monocentric (related to only one dispersal centre), whereas others are polycentric (distributed in several poles). Main conclusions The Chaquean xeromorphic forests are considered as a climax, with a stable composition resulting of the saline soil conditions. The Chaco acts as an edaphic barrier to many species, although the migration of some non‐Chaquean species is made possible by the net of gallery‐forests and low montane forests between the Río Paraguay and the Andean Piedmont. The Cerrado and the Chaco can be considered as a barrier limiting the expansion of the Paranean forest. This latter formation is a semi‐deciduous forest made of a mix of monocentric and polycentric elements. The numerous species found both in Colombia and in Paraná indicate that bridges exist, or have existed, between these two poles. The persistence in the Paraguay‐Paraná Basin of a moist forest made of the Paranean assemblages highlighted in this study confirms the hypothesis of moister and cooler phases than today.     

Morphological and genetic divergence of a small stream fish species along a watershed

Piabina argentea is a species of Characidae family that is widely distributed in the hydrographic basins of the São Francisco and Paraná Rivers and in some Atlantic coastal drainages of South America. The genus contains only one other species, which is restricted to the Tietê River headwaters (the Upper Paraná River Basin) and is considered monophyletic within the Stevardiinae subfamily. Despite the apparent morphological conservation of at least six well-structured clades, great genetic distance revealed by DNA barcoding has already been reported. In an attempt to evaluate the effect of the watershed of the two river basins in the Arc of Upper Paranaíba region (Upper Paraná and São Francisco River basins), we analyzed the populations from both basins using mitochondrial DNA sequences and morphometry and constructed a distribution scenario for the species in both basins.     

First record of non‐native hybrid catfish Pseudoplatystoma reticulatum × Leiarius marmoratus in the Upper Paraná River basin,Brazil

The aim of this study is to report the presence of a three non‐native hybrid long‐whiskered catfishes (family Pimelodidae) in the Upper Paraná River basin, Brazil. Genetic analyses demonstrated that the three presumptive hybrids were a result of the crossbreeding of Pseudoplatystoma reticulatum (central Amazonas River basin and Lower Paraná River) and Leiarius marmoratus (Amazonas, Essequibo and Orinoco rivers), producing a hybrid commonly known in Brazil as cachandiá. The potential threat to biodiversity, due to possible genetic contamination, competition and predation of wild stocks, of such artificially produced hybrid fishes is discussed.     

Invasibility of reservoirs in the Paraná Basin,Brazil, to <Emphasis Type="Italic">Cichla</Emphasis><Emphasis Type="Italic">kelberi</Emphasis> Kullander and Ferreira, 2006

The invasion process comprises not only the characteristics of nonindigenous species but also the attributes of the invaded environment which make it susceptible to the establishment of nonindigenous species. Habitat attributes operate like filters in determining the establishment of introduced species and the invasibility of a region. In the Upper Paraná River Basin, Brazil, the practice of introducing species was quite common and frequently carried out by hydroelectric companies. The target species of the present study, the peacock-bass Cichla kelberi, is native to the Amazon Basin. This species was introduced into several reservoirs of the Upper Paraná River Basin and is dispersing rapidly throughout the system. This study shows which characteristics of the reservoirs facilitate their invasibility after testing for the effect of propagule pressure. We conclude that a set of abiotic factors favors the invasibility of these reservoirs. To be more precise, the largest, deepest, most transparent and warmest reservoirs are the most likely to be colonized by Cichla kelberi. It is possible that other environments with similar characteristics to these reservoirs, such as the lagoons from the Upper Paraná River Basin floodplain, can also be colonized by Cichla kelberi.     

Genetic structure and evidence of anthropogenic effects on wild populations of two Neotropical catfishes: baselines for conservation

Genetic diversity and structure of Pseudoplatystoma corruscans and P. reticulatum, large migratory South America catfishes, where overfishing and the construction of numerous dams in their feeding and reproducing areas are affecting their migratory processes negatively, were studied using microsatellites in samples from Paraguay (that comprises the Pantanal biome), and the upper and lower Paraná Basins. Genetic diversity was in accordance to that observed for other large migratory fishes, but the most geographically isolated populations of P. reticulatum and those P. corruscans subject to anthropogenic effects (stocking and dams) showed lower genetic diversity and evidences of bottlenecks compatible with low effective population size. Pseudoplatystoma reticulatum presented subtle genetic differentiation within the Paraguay area, especially between the edges of its distribution. Pseudoplatystoma corruscans, in this same area, presented a quite homogeneous but significant genetic break between the Paraguay and upper Paraná populations, apparently resulting from natural and historical isolation between the basins until recently. These data demonstrates that, although these Pseudoplatystoma spp. are abundant in the Pantanal area, anthropogenic events are leading to negative effects on their populations, particularly in the upper Paraná Basin. Genetic differentiation observed along each species distribution demands conservation actions to preserve each population's biodiversity. These results represent important genetic information using new microsatellite markers and the first genetic study of P. reticulatum covering this area of its native distribution. Data may also contribute to a better understanding of species migration patterns and to be used as a baseline for proper management.     

Isolation and characterization of microsatellite loci in Piaractus mesopotamicus and their applicability in other Serrasalminae fish

The subfamily Serrasalminae (Characidae, Teleostei) is an endemic Neotropical group of fishes distributed along the Amazon, Paraná‐Paraguay and Orinoco Basins. The pacu (Piaractus mesopotamicus) is found in all major rivers that comprise the Pantanal of Mato Grosso. In order to investigate population genetic structure within the group, an enriched microsatellite library was constructed. Eight polymorphic were loci screened, with an average of 6.5 alleles per locus. Five loci exhibited greater than 60% heterozygosity. Additionally, a high level of cross‐species amplification was obtained.     

Sinusichnus, a trace fossil from Antarctica and Venezuela: expanding the dataset of crustacean burrows

The sinusoidal decapod crustacean burrow Sinusichnus sinuosus is documented from the Upper Cretaceous Hidden Lake Formation of James Ross Island (Antarctica), the Upper Oligocene-Lower Miocene Naricual Formation of the Eastern Venezuela Basin, and the Middle Miocene Socorro Formation of the Falcón Basin of Western Venezuela, significantly expanding its geographical and palaeolatitudinal range. These burrows may have served for bacterial farming in relatively stressful settings characterized by deltaic progradation. Sinusichnus sinuosus seems to display a broad latitudinal range, from low latitude tropical settings (Venezuela) to intermediate latitude temperate areas (Spain and France), and high latitude cold waters (Antarctica). The appearance of S. sinuosus in the Cretaceous reveals the acquisition of more sophisticated feeding strategies by decapod crustaceans, reflecting the dominance of the Modern Evolutionary Fauna.     

Length‐weight relationships for 55 freshwater fish species from the Iguatemi River,Upper Paraná River basin,Brazil

This study reports the length‐weight relationship estimatives (LWRs) for 55 fish species caught in the Iguatemi River drainage, Upper Paraná River Basin, Mato Grosso do Sul State, Brazil. The LWRs of 15 of the species are provided for the first time.     

Seasonal variation in genetic population structure of sábalo (Prochilodus lineatus) in the Lower Uruguay River

Prochilodus lineatus is a highly migratory fish species that sustains the most important commercial fishery of Paraná-Paraguay basin. Migratory patterns are poorly known and only few population genetic studies are available for this species in the Upper Paraná. To assess genetic population structure, we genotyped a sample of 93 individuals from the Lower Uruguay River close to Gualeguaychú city (Entre Ríos, Argentina) at three different times, July 2008 (Winter), September 2008 (Spring) and May 2009 (Fall). All individuals were genotyped for 12 microsatellite loci previously found to be informative to assess populations of P. lineatus. Our results show seasonal variation of the genetic sub-structuring at this locality that may be related to the presence of different migratory stocks throughout the year. The Fall sample includes an additional genetic cluster of individuals not detected in Winter and Spring, suggesting that this species should be considered a mixed stock fishery.     

Homogenization of freshwater fish faunas after the elimination of a natural barrier by a dam in Neotropics

Aim We quantify biotic homogenization of fish fauna caused by the elimination of a natural barrier between two freshwater ecoregions. We also evaluated fish introductions by different mechanisms such as aquaculture, angling and the aquarium trade in the homogenization of fish assemblages. The relative importance of native extinctions in the homogenization process was assessed by simulating the exclusion of threatened species in the data set. Location Paraná River, south‐eastern South America. Methods A fish species list of the Parana River Basin was organized in a subset of species distributions, according to pre‐ and post‐introductions caused by the elimination of the natural barrier and by other mechanisms. Biotic homogenization was verified by the use of Jaccard’s and Bray–Curtis’s coefficients, Whittaker’s beta diversity index, non‐metric multidimensional scaling analysis (NMDS) and nonparametric tests. Results For all subsets of species distributions, we observed an increase in the number of non‐native species in common related to the introductions. Between 40 and 52% of the species currently present in the Upper Paraná Basin dispersed upstream from the Lower Paraná after the construction of Itaipu Dam, including at least 1 class, 2 orders, 4 families and 16 genera of fish. Jaccard’s coefficient between the Upper and Lower Parana River increased by 6–7.5% only considering the Itaipu Dam influence and 10.5% considering all mechanisms of fish introductions. More than 50% of the increase in similarity was caused by the elimination of the barrier. Our results indicated functional homogenization related to large‐bodied Siluriformes (catfish). Main conclusions Itaipu Lake flooded a natural barrier and allowed hydrologic connectivity between the Upper and Lower Paraná River, and many fishes of the lower part of the river were able to colonize the upper stretches. The homogenization of the two assemblages between these adjacent aquatic regions was an unpredicted result of hydropower implementation. Introductions by dam can also shift longitudinal and latitudinal body size patterns (i.e. Bergmann's rule).