Influence of hydrological changes on the fish community in two lotic environments of the Middle Paraná Floodplain,Argentina

Temporal variations of fish abundance and species richness in two sites of a secondary channel of the Middle Paraná Floodplain (Argentina) have been analyzed from 2010 to 2012. Relationships of these ecological attributes with alternations of floods and dry periods were appraised. Permutational analyses of variance were applied to determine significance in temporal changes of the fish community, taking into account catch per unit effort and species richness of the whole community, by groups of distinct reproductive strategy and considering fish sizes. The results reveal significant differences in structure and composition of fish assemblages at distinct stages of the hydrological regime. Those temporal differences are associated with changes in timing, duration, and magnitude of floods since the three groups have shown distinct responses to the hydrological variations. Long-distance migrants depend on major inundations for a successful reproduction, short-distance migrants seem to have distinct responses to floods according to the kind of species, and sedentary fish-developing parental care essentially needs high floodplain connectivity for juvenile development.     

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.     

Ecological responses of two pioneer species to a hydrological connectivity gradient in riparian forests of the lower Paraná River

The vegetation of the Paraná River floodplain has physiognomic, structural and ecological characteristics that are distinct from those of the surrounding landscapes across the river (Forest, Chaco Savannahs, Pampean steppe). Few species are able to live in the alternately flooded and dry soil. The distribution of each species is strongly conditioned by the water regime in each area of the floodplain, and its location in the topographical gradient of the islands allows us to determine the possibility of colonising the bars and islands of the river course to determine their tolerance to hydrological variations and to foresee the changes that can take place as a result of disturbances in the hydrological regime. Here, we present the occurrence of willow (Salix humboldtiana Willd.) and South American alder (Tessaria integrifolia Ruiz et Pav.) in bars and islands of different topographies in a section of the Paraná River downstream from the confluence of the Paraguay and Paraná rivers. The results indicate that both species have similar niches in relation to hydrological fluctuations. However, willow was significantly more frequent at of 48.49 m a.s.l., while palo bobo reached its highest frequency at 49.29 m a.s.l. The difference between the modes of the distribution curves of each species was 0.80 m. Canopy trees such as willow and palo bobo are adapted to flooded soil conditions for 77.8 and 40% of their respective lives and survive with a long-lasting inundation phase (306 and 366 days, respectively). However, many trees in the Paraná River floodplain died when the flood period extended for more than 1 year.     

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.     

Environmental factors exert predominant effects on testate amoeba metacommunities during droughts in floodplains

Metacommunities have been evaluated as models for the relative importance of environmental and spatial processes in assembling ecological communities. Here, we tested the hypothesis that different hydrological periods (drought and flooding) influence the environmental associations of planktonic testate amoeba metacommunities. We predicted that environmental factors would exert the strongest effects on species dispersal under drought, but that they would be less significant during flooding. Testate amoebae were sampled during drought and flooding, from 72 lakes in four Brazilian floodplains (Amazonian, Araguaia, Pantanal and Paraná). Partial redundancy analysis indicated that only environmental factors were significant; they were significant in all floodplain lakes during the drought. Only the Paraná floodplain had significant results for environmental factors during both hydrological periods. Spatial factors did not contribute significantly to any of the metacommunities. The depth, pH and variables related to environmental productivity were identified as major predictors in the assembly of testate amoeba communities. Our results highlight that different hydrological periods vary in their relative importance in environmental and spatial processes. The species‐sorting model was predominant during drought, while stochastic processes prevailed during flooding in all but the Paraná floodplain. In the Paraná floodplain, the construction of dams could potentially alter the effects of environmental and spatial factors on the dispersal of planktonic testate amoebae. The pH and the environmental productivity factors were largely responsible for species selection and the structuring of the planktonic testate amoebae metacommunities in Brazilian floodplains.     

The recently established diatom Coscinodiscus wailesii (Coscinodiscales, Bacillariophyta) in Brazilian waters. I: Remarks on morphology and distribution

Coscinodiscus wailesii Gran et Angst is a large centric diatom (280–500 μm diameter) from marine phytoplankton, characterized by a cylindrical frustule with flat valvar surface, two marginal rings of rimoportulae on the mantle, and two macrorimoportulae. Cells from cultured and natural populations collected in Paranaguá Bay, Paraná, southern Brazil were observed under light and scanning electron microscopes to verify the populations’ correct identity and morphology. In both populations, a typical central rosette or a hyaline area was found in the valvar center. The species’ distribution in Brazilian waters was revised, and a discussion on possible vectors of transport was made. Blooms of the species occur sporadically in the coast of Paraná, seeming to affect the local trophic chain.     

Temporal organization of fish assemblages in floodplain lagoons: the role of hydrological connectivity

The present study evaluated the hypothesis that after flooding events, non-random patterns of species co-occurrence (segregation) are progressively intensified in fish assemblages inhabiting seasonally isolated lagoons. We sampled lagoons in the upper Paraná River floodplain between 1992 and 1993, and classified them into five hydrological phases, according to their surface connectivity. During the period of isolation (9 months), lagoons depth decreased progressively, but desiccation was reversed after 4 months (possibly due to groundwater infiltration and rainfall). A significant co-occurrence pattern (segregation) occurred in the last phase, supporting our initial hypothesis. However, richness, abundance and composition were significantly correlated with habitat depth, indicating that assemblage structure and organization is closely associated with dynamics of habitat retraction/expansion during isolation. Although environmental conditions of lagoons (absence of prolonged desiccation) prevented an adequate test of our hypothesis, our data suggests that, in addition to the importance of surface floods, the hydrological cycle as a whole has a crucial role shaping the organization of fish assemblages in floodplain lagoons seasonally isolated.     

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.     

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.     

Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

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New species of glass knifefish genus Eigenmannia (Gymnotiformes: Sternopygidae) with comments on the morphology and function of the enlarged cephalic lateral-line canals of Sternopygidae

A new species of Eigenmannia is described from the Rio Paraná (the Grande, Paranapanema and Tietê basins). This new species is distinguished from all congeners by colouration pattern, position of the mouth, relative depth of posterodorsal expansion on infraorbitals 1 + 2, number of teeth, osteological features, number of rows of scales above lateral line (LL) and morphometric data. Comments on the widened cephalic lateral-line canals of Sternopygidae and a dichotomous key to the species of Eigenmannia from the Rio Paraná Basin are provided.     

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)     

Cytogenetic studies on Apareiodon affinis (Pisces, Characiformes) from Paraná river basin: sex chromosomes and polymorphism

Comparative cytogenetic studies were carried out on Apareiodon affinis from an important hydrographic system at South America, the Paraná river basin. Two distant regions were chosen, which were separated by Guaíra Falls (formerly Sete Quedas); the region in the upper part of the hydrographic basin is called Upper Paraná (Brazil), whereas and the other in the lower part is called Lower Paraná (Argentina). Individuals from Upper Paraná have diploid numbers of 2n = 54 (NF = 108) for males and 2n = 55 (NF = 110) for females, showing female heterogamety with a ZZ/ZW₁W₂ multiple sex chromosomes system that is endemic for the region. In different localities at Lower Paraná, the specimens presented diploid number of 2n = 54 for both sexes, without any sex chromosomes heteromorphism. However, they have an accentuated polymorphism characterized by variation in number of acrocentric chromosomes, constituting something new for family Parodontidae. The most likely hypothesis to explain the origin of such polymorphism is based on successive pericentric inversions giving rise to acrocentric chromosomes. Thus, it was possible to detect 10 cytotypes along the Lower Paraná basin. Such chromosomal variations possibly are the consequence of an adaptative process. Our data probably indicate the occurrence of distinct species in each region that share the same denomination. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Has the bumblebee <Emphasis Type="Italic">Bombus bellicosus</Emphasis> gone extinct in the northern portion of its distribution range in Brazil?

Evidence for the extinction of the bumblebee Bombus bellicosus in Paraná state, in Brazil, is presented. The species is found in areas covered with open grass fields and shrub vegetation, originally ranging from northwestern Argentina to Paraná, where it reached its northeastern limit. Until the early 1980s, B. bellicosus was relatively abundant in Paraná, when the last known specimens were collected. In recent surveys conducted from 2002 to 2005, no specimens were recovered at sites in which the species was previously known to occur. Possible causes for local extinction of this species are discussed, including habitat conversion, pollution and climate change.     

Shell Beds as paleoecological puzzles: A case study from the Upper Permian of the Paraná Basin, Brazil

Summary Microstratigraphic, sedimentological, and taphonomic features of the Ferraz Shell Bed, from the Upper Permian (Kazanian-Tatarian?) Corumbataí Formation of Rio Claro Region (the Paraná Basin, Brazil), indicate that the bed consists of four distinct microstratigraphic units. They include, from bottom to top, a lag concentration (Unit 1), a partly reworked storm deposit (Unit 2), a rapidly deposited sandstone unit with three thin horizons recording episodes of reworking (Unit 3), and a shell-rich horizon generated by reworking/winnowing that was subsequently buried by storm-induced obrution deposit (Unit 4). The bioclasts of the Ferraz Shell Bed represent exclusively bivalve mollusks.Pinzonellaillusa andTerraia aequilateralis are the dominant species. Taphonomic analysis indicates that mollusks are heavily time-averaged (except for some parts of Unit 3). Moreover, different species are time-averaged to a different degree (disharmonious time-averaging). The units differ statistically from one another in their taxonomic and ecological composition, in their taphonomic pattern, and in the size-frequency distributions of the two most common species. Other Permian shell beds of the Paraná Basin are simílar to the Ferraz Shell Bed in their faunal composition (they typically contain similar sets of 5 to 10 bivalve species) and in their taphonomic, sedimentologic, and microstratigraphic characteristics. However, rare shell beds that include 2–3 species only and are dominated by articulated shells preserved in life position also occur. Diversity levels in the Permian benthic associations of the Paraná Basin were very low, with the point diversity of 2–3 species and with the within-habitat and basin-wide (alpha and gamma) diversities of 10 species, at most. The Paraná Basin benthic communities may have thus been analogous to low-diversity bivalve-dominated associations of the present-day Baltic Sea. The ‘Ferraz-type’ shell beds of the Paraná Basin represent genetically complex and highly heterogeneous sources of paleontological data. They are cumulative records of spectra of benthic ecosystems time-averaged over long periods of time (10²–10⁴ years judging from actualistic research). Detailed biostratinomic reconstructions of shell beds can not only offer useful insights into their depositional histories, but may also allow paleoecologists to optimize their sampling designs, and consequently, refine paleoecological and paleoenvironmental interpretations.     

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.

     

Hydrological connectivity determining metacommunity structure of planktonic heterotrophic flagellates

Dispersal potential of organisms is directly related to the hydrological connectivity among habitats. We investigated if the relative role of the environmental and spatial components in structuring the heterotrophic flagellates depends on the degree of hydrological connectivity. Samplings were performed in aquatic environments of the Paraná River floodplain, which differ in their degree of connectivity: lotic environments, connected lakes and isolated lakes (temporarily connected to the main river only during floods). We expect that communities in isolated lakes would be more subject to dispersal limitation, while in connected lakes and lotic environments the communities would be regulated mainly by environmental variables (species sorting). We sampled in the pelagic region of 23 environments during the low water period in 2014. The results of pRDA revealed that the contributions of environmental and spatial factors differed between the types of environments. The greater contribution of the environmental variables in structuring the flagellates metacommunity, regardless of the type of environment, may be related to the elevated dispersal capacity of microorganisms. The spatial component was also significant in the isolated lakes. Our results support the idea that microorganism communities are mainly structured by environmental factors, although the spatial component seems important when lakes are isolated.     

Environmental predictors of the occurrence of exotic <Emphasis Type="Italic">Hydrilla verticillata</Emphasis> (L.f.) Royle and native <Emphasis Type="Italic">Egeria najas</Emphasis> Planch. in a sub-tropical river floodplain: the Upper River Paraná, Brazil

The Upper River Paraná Floodplain System comprises the rivers Ivinheima, Baía and Paraná, which with their associated waterbodies form three subsystems, each showing individual characteristics. Hydrilla verticillata recently invaded the Upper Paraná Floodplain, while Egeria najas is the native most abundant submersed macrophyte. A large flood-pulse, during January–March 2007, abruptly reduced macrophyte stands in many areas to near-zero and dispersed propagules over the entire floodplain. From April 2007 to April 2008, we conducted three surveys sampling for the presence–absence of H. verticillata and E. najas and environmental variables aiming to answer: (1) How rapid is the colonization–regeneration process for both species? (2) Which habitats seem to be more susceptible to their colonization? (3) Which environmental factors can best predict their occurrence? Neither H. verticillata nor E. najas colonized the Ivinheima subsystem. In the Baía subsystem, E. najas had only two occurrences while H. verticillata was not present. In the Paraná subsystem, E. najas predominantly occurred in river channels, but it was also common in floodplain lakes. In April 2007, it was found in 13% of the sites in the Paraná subsystem, increasing to 30% in November 2007 and reaching 34% in April 2008. H. verticillata did not successfully colonize floodplain lakes of the Paraná subsystem. In channels, it had 34% occurrence in April 2007, increasing to 62% in November 2007 and remaining at 62% in April 2008. The role of environmental variables in predicting species occurrence changed depending upon the scale of the analysis. Considering the whole Upper Paraná floodplain, water transparency followed by electrical conductivity were the strongest predictors for both species. Colonization by submersed plants seems improbable in the Ivinheima subsystem owing to its low water transparency besides frequent localized floods; in the Baía subsystem, it seems inhibited by transparency and low alkalinity. Considering just the Paraná subsystem, the proportion of organic matter in sediment, ten times higher in floodplain lakes than in channels, was the best predictor for H. verticillata occurrence (also related to water pH and transparency), while E. najas was only significantly explained by transparency.