Influence of large South American rivers of the Plata Basin on distributional patterns of tropical snakes: a panbiogeographical analysis

Aim The main drainages of the Plata Basin – the Paraná, Paraguay and Uruguay rivers – begin in tropical latitudes and run in a north–south direction into subtropical–temperate latitudes. Consequently, the biota of these rivers has tropical elements that contrast with temperate biomes through which the rivers run. We apply a panbiogeographical approach, to test whether the large rivers of the Plata Basin have a differential influence on distributional patterns of tropical snakes in subtropical and temperate latitudes of South America. Location Subtropical and temperate sections of the major Plata Basin rivers, South America. Methods We compared the individual tracks of 94 snake taxa. The track analysis consisted of: (1) plotting the localities of each taxon on maps, (2) connecting the localities of each taxon using a minimal geographical proximity determinant of the ‘individual tracks’, and (3) superimposing the individual tracks to determine generalized tracks. To detect tropical snakes that reach higher latitudes through the rivers we used the preferential direction of distribution concept. For each taxon we measured the angular deviations between the line of its individual track and the course of the rivers in a 100 × 100 km scaled grid. Average angular values < 45° indicated a positive association with the rivers. Results Thirty‐five of 94 taxa showed distributions associated with the major rivers of the Plata Basin, including fauna from distinct biogeographical lineages, supported by the occurrence of five generalized tracks as follows: (1) the Paraguay–Middle Paraná, (2) the Paraguay–Paraná fluvial axis, Upper Paraná and Middle Paraná to Upper Delta, (3) the Lower Paraguay, Paraná and Uruguay rivers, excluding the sectors High Paraná and High Uruguay, (4) the Uruguay River and Upper Paraná, and (5) the High Paraná. The Atlantic species occurred with significantly higher frequency in the Uruguay River and High Paraná river sections, the Amazon species were found with significantly higher frequency in the Paraguay and Middle Paraná sections, and the species with a Pantanal distribution were found in all sections. Main conclusions The observed distributional patterns may be explained by the interaction of ecological, geographical and historical factors. Previous authors have developed ecological (hydrological or environmental similarity) or dispersalist (effect of rivers as migration routes) explanations. The coincidence between generalized tracks and past geomorphological events that caused displacements and changed relationships between the Paraguay, Paraná and Uruguay river sections supports hypotheses involving the strong influence of historical factors in the present configuration of tropical snake distribution in temperate latitudes.     

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     

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.     

Periphytic diatom ecological guilds in floodplain: Ten years after dam

Periphytic diatoms are a key primary producer in floodplain systems. In this study, we assessed the species and functional traits in the periphytic diatom community in three lentic environments directly connected to the Paraná River shortly after damming and a decade later. Samples were collected in 2001–2002 and 2010–2011 during high waters phase. Periphytic samples were obtained from Eichhornia azurea Kunth, found in the shore zone of these environments. We recorded a total of 90 diatom species. 47 taxa were exclusive during the period shortly after damming and 18 taxa were only found in 2010–2011. The analysis of the similarity, diversity, beta diversity and non-metric multidimensional scaling (NMDS) suggested that there were differences in the species and functional traits of the periphytic diatom community between the two study periods. Variations in water transparency and nutrient (including nitrogen and phosphorus forms) were the most important variables shaping diatom communities diatoms during the study periods. High and motile profiles were characteristic shortly after damming and taxa of high and low profiles predominated a decade later. High transparency, high water and nitrogen levels favored the development of high and low profile, such as Gomphonema augur var. augur, Synedra goulardii and Amphora sp., whereas taxa belonging to high-profile and motile algae (e.g., Eunotia indica, Nitzschia amphibia) were found in the opposite conditions. Species turnover was an important diversity component that was greatly influenced by limnologic differences over time, represented by environmental and temporal dissimilarities between the years. These changes reinforce the modifications that have occurred in the environmental component of the Upper Paraná River floodplain downstream of the dam from the start of its operation.     

The Application of Chironomid Pupal Exuvial Technique (CPET) for Ecological Analysis in a Neotropical Large River System

This field ecological study, based on the chironomid pupal exuvial technique (CPET), is new for the Paraná River and proposes an efficient tool to be used in future ecological approaches and biomonitoring. Drifting of pupal exuviae in a river-floodplain system of the Middle Paraná River floodplain was represented by 34 Chironomidae taxa, being the characteristic association obtained from the CPET: Lopescladius, Onconeura, Paralauterborniella, Polypedilum, and Harnischia complex. Diversity, richness, dominance, total density, and density of dominant taxa were different between the longitudinal and lateral dimensions but not between hydrologic phases, with a greater diversity and richness in the main channel of the river and higher density and dominance in floodplain habitats. The species turnover is the dominant process in structuring studied assemblages in spatial and temporal analysis, increasing in the floodplain habitats and in low-water phase. The results obtained showed that drifting exuviae in the longitudinal axis were coming from different assemblages and environments of a wider area (regional), while exuviae recorded in the connections of the floodplain environments in the lateral dimension could reflect the local assemblages. We demonstrated the ecological value of CPET studies to interpret the attributes of Chironomidae assemblage in river-floodplain systems of large rivers in an integrated way.     

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.     

Trophic ecology and metabolism of two species of nonnative freshwater stingray (Chondrichthyes: Potamotrygonidae)

The stingrays Potamotrygon amandae and Potamotrygon falkneri are nonnative species established in the Upper Paraná basin. Although they are widely distributed, few studies on their diets or respective metabolic responses exist. Therefore, the aim was to evaluate the dietary composition, trophic niche breadth and lipid/protein concentrations in muscle and hepatic tissues of these two species, as well as the interrelationships between them. The individuals were collected in two areas on the Upper Paraná River. The stomachs and samples of muscle and liver tissues were taken for analysis. A broad dietary spectrum was observed for both species, along with differences in dietary composition, with a higher consumption of detritus by P. amandae and Baetidae by P. falkneri. No differences were observed in the trophic niche breadth. Regarding the metabolic variables, differences were only found in the hepatic protein, with a higher content observed in P. falkneri. A significant positive correlation was observed between items of animal origin and detritus with muscle protein for this species. This shows that such feeding habits, which are characteristic of a generalist, influenced the metabolism of the species and possibly contributed to the successful adjustment of the species to new habitats in the Upper Paraná River.

     

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.     

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.     

Length-weight relationships for seven endemic fish species from streams of the last two large remaining dam-free tributaries of the Upper Paraná River Floodplain in the Paraná State,Brazil

This study reports the length-weight relationships (LWR) for seven endemic fish species from streams in the Ivaí (Characidium heirmostigmata, Corydoras lacrimostigmata, Curculionichthys oliveirai, Hisonotus pachysarkos, and Cambeva horacioi) and Ivaí and Piquiri (Apareiodon vladii and Planaltina kaingang) River basins, Paraná State, Brazil. Fish specimens measured and weighed were collected between November 1994 and July 2019, fixed with 10% formalin, and are preserved in 70% alcohol. Measurements were done for standard length (SL—0.1 cm precision) and total weight (TW—0.01 g precision). All coefficient of allometry obtained is within the general range for fishes representing useful tentatives for LWR parameters. We highlight the importance of information about the biology of the endemic fish species in a crucial area for the biodiversity conservation of the Upper Paraná River system.     

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.     

Distribution of non‐native suckermouth armoured catfish Pterygoplichthys ambrosettii in the upper Paraná River basin,Brazil

This study describes the invasion of the upper Paraná River basin by Pterygoplichthys ambrosettii based on a literature review and field samples. Pterygoplichthys ambrosettii has been reported in 42 localities throughout the upper Paraná River basin, including the Tietê, Paranapanema, Paraná, Grande and Aguapeí rivers. The ascent of P. ambrosettii after the inundation of the Sete Quedas Falls on the Paraná River and the release of individuals by aquarium hobbyists were the primary drivers of this invasion.     

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.     

Spatial and temporal variations among fish with similar strategies: patterns of reproductive guilds in a floodplain

Seasonal flooding regimes are closely related to the life history of neotropical fish, especially with regard to their reproduction. The classification of fish into reproductive guilds serves to identify broad patterns in reproductive types, which are important in developing management and conservation measures. We tested the hypothesis that the fish reproductive guilds in the Upper Paraná River floodplain exhibit spatial and temporal distributions. Samples were taken each quarter in 2010 from several environments (i.e., biotopes) and rivers of the plain. Fish were categorized into four reproductive guilds based on migration, external fertilization, and parental care. Moreover, the abundance and species richness within each guild were used to evaluate their patterns. Guilds were spatially structured, possibly due to species dispersion as well as the influence of the hydrological and limnological characteristics of the biotopes and rivers of the plain. The Paraná River presented lower analyzed metric values, which demonstrates the negative effects of the dam built upstream of the study area. The guilds also presented temporal structure. During the flood season, the guilds presented similar spatial structures, and the local environmental characteristics led to spatial differentiation in the structure of guilds (i.e., flooding promoted the homogenization of the reproductive guilds).     

Phytoplankton alpha diversity as an indicator of environmental changes in a neotropical floodplain

Habitat fragmentation, overexploitation of natural resources, the introduction of alien species and environmental degradation in aquatic environments are the main causes of reductions in aquatic biota diversity. Phytoplankton represent good ecological indicators because they are highly diverse and rapidly respond to a wide array of environmental disturbances. We investigated the interannual variation in alpha diversity of the phytoplankton community in lakes of an alluvial floodplain. We predicted that the phytoplankton diversity decreases over time in lakes and rivers subjected to human activities, whereas those biotopes in areas under pristine environmental conditions do not show a reduction in alpha diversity. Phytoplankton samples were taken quarterly over a period of eleven years (2000–2010), from ten localities associated with three large rivers, which showed different uses of the watershed. The time series of alpha diversity was analysed, to assess the temporal trend, in addition to their relationships with environmental factors. Phytoplankton alpha diversity in the Upper Paraná River floodplain ranged between 4 and 87 species and showed a mean of 30 (±16.5). Sites associated with the Paraná River showed a decline in diversity, which was associated with transparency, nitrogen and phosphorus forms. These results reflect a combination of seston retention by damming and an increase in the N:P ratio, which appears to negatively affect phytoplankton diversity. If temporal trends in environmental variation and the phytoplankton community remain, the future consequences for phytoplanktonic diversity in the Paraná subsystem will be severe, which might cause changes in the trophic structure and dynamics, and therefore in the functioning of environments, since this community is one of the main sources of energy for other trophic levels.     

Identifying priority areas for invertebrate conservation using land snails as models

Mollusca is a megadiverse phylum with an estimated number of 70,000–76,000 described species which can inhabit a wide variety of environments. Among them, land snails are a main component of terrestrial ecosystems and they play a pivotal role in ecosystem functioning. They are suffering habitat loss, overexploitation and competition from introduced species, but are regarded as a “non-charismatic” group for conservation purposes. Orthalicoidea is a dominant faunal element in the Neotropics and in Argentina includes 104 species that inhabit a variety of environments. Their abundance, diversity, comprehensive taxonomy and widespread representation in different ecoregions makes this molluscan group an excellent model for biodiversity assessments. The database used here consisted of 985 unique geographic records of 104 species. Species distribution models were generated using the Maximum Entropy method and Zonation v 3.1 was used to evaluate the proposed conservation goals. Three analyses including species distributions, the current protected areas system (PAs) and the Human print layer were carried out. This allowed the identification of priority areas for conservation, the percentage of the species distribution under PAs and analysis of the potential impacts under current land use and in the priority areas detected above. Sixty-one species were modeled, and 59 of them were included in the priority area selection process due to their high area under curve (AUC) scores. Five high priority areas located in the different ecoregions, were identified: 1-dry Chaco, 2-humid Pampas, 3-Southern Andean Yungas, 4-Alto Paraná Atlantic Forests and 5-high Monte. A small percentage of the average distribution range of Orthalicoidean species (3%) was within the current protected areas. Highest-ranked priority areas for land snails are outside the current protected areas system. When human impact is considered, the priority areas are reduced in size and appear as small patches. However, highest priority areas for conservation continue being those detected in the above analyses. Most of the areas detected are used for economic purposes, creating conflicts of interest between the development of human activities and conservation. This study represents one of the first attempts to identify ecoregion level priority areas for a terrestrial invertebrate group. Further analyses, including new predictors and other molluscan taxa, would improve planning the conservation of poorly known invertebrate groups.     

Transcontinental dispersal,ecological opportunity and origins of an adaptive radiation in the Neotropical catfish genus Hypostomus (Siluriformes: Loricariidae)

Ecological opportunity is often proposed as a driver of accelerated diversification, but evidence has been largely derived from either contemporary island radiations or the fossil record. Here, we investigate the potential influence of ecological opportunity on a transcontinental radiation of South American freshwater fishes. We generate a species‐dense, time‐calibrated molecular phylogeny for the suckermouth armored catfish subfamily Hypostominae, with a focus on the species‐rich and geographically widespread genus Hypostomus. We use the resulting chronogram to estimate ancestral geographical ranges, infer historical rates of cladogenesis and diversification in habitat and body size and shape, and test the hypothesis that invasions of previously unoccupied river drainages accelerated evolution and contributed to adaptive radiation. Both the subfamily Hypostominae and the included genus Hypostomus originated in the Amazon/Orinoco ecoregion. Hypostomus subsequently dispersed throughout tropical South America east of the Andes Mountains. Consequent to invasion of the peripheral, low‐diversity Paraná River basin in southeastern Brazil approximately 12.5 Mya, Paraná lineages of Hypostomus, experienced increased rates of cladogenesis and ecological and morphological diversification. Contemporary lineages of Paraná Hypostomus are less species rich but more phenotypically diverse than their congeners elsewhere. Accelerated speciation and morphological diversification rates within Paraná basin Hypostomus are consistent with adaptive radiation. The geographical remoteness of the Paraná River basin, its recent history of marine incursion, and its continuing exclusion of many species that are widespread in other tropical South American rivers suggest that ecological opportunity played an important role in facilitating the observed accelerations in diversification.     

Sympatry between <Emphasis Type="Italic">Alouatta caraya</Emphasis> and <Emphasis Type="Italic">Alouatta clamitans</Emphasis> and the rediscovery of free-ranging potential hybrids in Southern Brazil

Records of sympatry between Alouatta caraya and A. clamitans are rare despite their extensive range overlap. An example of their current sympatry and the rediscovery of free-ranging potential hybrids of A. caraya and A. clamitans in the forests of the Upper Paraná River, Southern Brazil, are reported in this paper. Eight groups were observed in the study area: five monospecific groups of A. caraya, two of A. clamitans, and a group containing two adult males and two adult females of A. caraya and a sub-adult male and two adult females identified as Alouatta sp. The color of the last three individuals was a mosaic between the two species; this is consistent with previously described variations in museum specimens collected in the Paraná River in the 1940s that had been identified as potential hybrids. The results from this study emphasize the need for scientific studies in the region of the Ilha Grande National Park, one of the few regions in the Paraná River that currently harbors both howler species. Contribution number 1637 of the Departamento de Zoologia, Universidade Federal do Paraná, Caixa Postal 19020, 81531-980, Curitiba, Paraná, Brasil.     

Acoustic homogeneity in the piranha Serrasalmus maculatus

Different studies suggest some social calls could be used in fish identification if their specificity is unambiguously assessed. Sounds of different populations of piranhas Serrasalmus maculatus Kner, 1858 were recorded to determine their homogeneity between rivers inside a single basin (Araguari and Grande River, upper Paraná River basin) and between separated basins (Amazon and Paraná basins). All fish from the different populations produced sounds with similar acoustic features. Consequently, the populations were not discernible based on individual sound characteristics. This high homogeneity between sounds from different populations indicates their usefulness for conservation projects using passive acoustic monitoring in piranhas. Moreover, it supports the use of acoustic features as complementary key characteristics in taxonomic studies.     

The Temporal Asynchrony of Planktonic Cladocerans Population at Different Environments of the Upper Paraná River Floodplain

The aim of this study was to investigate the existence of synchronic fluctuation patterns in cladoceran populations of the Upper Paraná River floodplain. The following hypothesis were tested: (i) the populations of a given species present the same fluctuation pattern in abundance for different environments and (ii) synchrony is higher when we consider subsets of neighboring environments or those belonging to the same category (e.g., lagoons, rivers). Samplings were performed every three months from February 2000 to November 2002 at 11 sites. To evaluate spatial synchrony, the intraclass correlation coefficient was used. The results showed no significant correlation for the most abundant species, meaning that fluctuation patterns of planktonic cladocerans were asynchronous. Asynchrony indicated that the influence of floods and regional climatic factors was not strong enough to synchronize the populations, suggesting that local factors were more important than regional effects in determining zooplankton abundance patterns. The implications of these results are that the observations from a single environment cannot be extrapolated to other environments in a manner that would allow its use as a sentinel site. This means that a monitoring program for floodplain systems, or at least for the Paraná River floodplain, has to comprise greater spatial extents. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)