Janet Higuti

Variation in ostracod (Crustacea, Ostracoda) communities in the alluvial valley of the upper Paraná River (Brazil) in relation to substrate

Large river floodplains are convenient model systems to test for variation in animal and plant community structure, as they have a variety of habitats and substrates and are generally dynamic systems through the occurrence of flood pulses with varying intensity. South American floodplain systems furthermore have unique types of substrates, in the form of root systems of floating macrophytes. Here, we investigate the variation in ostracod (small, bivalved crustaceans) communities in relation to substrates and related environmental variables. Sampling was effected in 2004 in the alluvial valley of the upper Paraná River, Brazil, in the wet and dry seasons. Five different substrates, including littoral sediment and four macrophyte species root and leaf systems, in four hydrological systems and a variety of habitat types, were sampled. Fifty-four species of Ostracoda were found. Variation partitioning analysis (RDA) showed that ostracod communities significantly differed between different substrates, mainly between the littoral and plants with small root systems (Eichhornia azurea) on the one hand, and plants with large and complex root systems on the other hand (Eichhornia crassipes and Pistia stratiotes). RDA analyses indicated that the pleuston (biotic communities associated with root systems of floating plants) of E. crassipes comprised more non-swimming species than the pleuston of the smaller roots of P. stratiotes, but species-level Kruskal–Wallis analyses could not detect significant differences between both macrophyte species. Also habitat type and hydrological systems contributed to variation amongst ostracod communities, but less so than the factor substrate. Abiotic factors also contributed to variation, but the ranges of all measured water chemistry variables were narrow. This uniformity in abiotic factors, which might be owing to the occurrence of large flooding events, unites all water bodies, even those that are generally separated.

Cyclopidae (Crustacea, Copepoda) from the upper Paraná River floodplain, Brazil

Cyclopid copepods from samples of fauna associated with aquatic macrophytes and plancton obtained in lotic and lentic environments were obtained from the upper Paraná River floodplain (in the states of Paraná and Mato Grosso do Sul, Brazil). Macrophytes were collected in homogeneous stands and washed. Plankton samples, taken from the water column surface and bottom, were obtained using a motor pump, with a 70 microns mesh plankton net for filtration. Twelve taxa of Cyclopidae were identified. Among them, Macrocyclops albidus albidus, Paracyclops chiltoni, Ectocyclops rubescens, Homocyclops ater, Eucyclops solitarius, Mesocyclops longisetus curvatus, Mesocyclops ogunnus, and Microcyclops finitimus were new finds for this floodplain. Eight species were recorded exclusively in aquatic macrophyte samples. Among these species, M. albidus albidus and M. finitimus presented greatest abundances. Only four species were recorded in plankton samples, and Thermocyclops minutus and Thermocyclops decipiens are limited to this type of habitat. Among these four species, T. minutus is the most abundant, especially in lentic habitats.

On the Strandesia obtusata/elliptica lineage (Ostracoda, Cyprididae) in the alluvial valley of the upper Paraná River (Brazil), with the description of three new species

We redescribe Strandesia tolimensis Roessler, 1990, originally described from Colombia, and describe three new species, Strandesia lansactohai n. sp., S. velhoi n. sp. and S. nupelia n. sp. from lakes, channels and rivers in the alluvial valley of the upper Parana River. Mainly valve morphology and shape and size of the attachment of the caudal ramus are used to characterize these species, as other soft parts are uninformative. All populations studied here are parthenogenetic, so male morphologies are not available. Sequences of the mitochondrial COI-gene are used to construct a phylogeny, as well as a genetic network of specimens, and in both analyses the four species are well-supported. In addition, we also delimit the four species with genetic distances using Birky’s K/θ method and conclude that it supports the identity of the species under consideration.

Composition and distribution of Darwinulidae (Crustacea, Ostracoda) in the alluvial valley of the upper Paraná River, Brazil

The occurrence and abundance of darwinulid ostracods, as well as environmental factors influencing these patterns, were investigated in the alluvial valley of the upper Paraná River. Ostracods were sampled from several substrates, like littoral sediments and pleuston, which included several aquatic macrophytes species, from 31 localities (lentic and lotic) belonging to different riverine systems. Eight darwinulid species were found, representing all genera from this family. Alicenula serricaudata, Vestalenula pagliolii, and Penthesilenula brasiliensis were the most common species. Cluster analysis based on the composition and abundance of darwinulid communities revealed the presence of five associations. Darwinula stevensoni, Vestalenula botocuda, and Penthesilenula aotearoa were almost exclusive to lotic environments. A Mantel multiple test showed that the occurrence and distribution of darwinulid ostracods were significantly related to types of habitat and systems, but not to abiotic variables. It thus seems that the hydrodynamic fluctuations of these environments are probably more important to darwinulid distribution than the limnological characteristics.

Benthic macroinvertebrate community structure in a stream of the north-west region of Paraná State, Brazil

This study aimed to survey the benthic macroinvertebrate fauna of a first order stream located in an agricultural area, and to assess the environmental factors involved in the spatial distribution of this community. Invertebrates were gathered in November 2007 at three sampling sites distributed along the Itiz Stream, located in Marialva municipality, Parana State. At each site, we measured the physical and chemical variables of the water, and then took four samples, using Surber sampler. In order to evaluate the differences in density, richness, diversity and evenness, we employed an ANOVA and a DCA to summarize biotic data. The invertebrates were categorized into functional groups and the BMWP score was applied to calculate the biological integrity of the environment. The faunal composition was represented by 103 taxa distributed across five phyla, of which the highest occurrence was of arthropods, especially insects. Higher density values were observed for Chironomidae, Ephemeroptera, Coleoptera and Trichoptera. The richness, diversity and density, as well as the density of gathering-collectors, were higher in the intermediate course of the stream. The distribution pattern of the taxa was mainly influenced by lentic or lotic characteristics of the sampled sites and microhabitats, as evidenced by the DCA. The BMWP indices indicated that the three sampling sites presented scores of excellent and good water quality. In the Itiz Stream, the presence of preserved marginal vegetation and the distance from urban centers that generate pollution, combined with peculiarities of each sampling site, influenced the structure of the benthic community.

Association of body size and behavior of freshwater ostracods (Crustacea, Ostracoda) with aquatic macrophytes

In aquatic systems, macrophytes play an important role in habitat structuring and can be relevant for the establishment and/or mobility of the organisms and might thus influence species composition. This study evaluates the influence of the structural complexity of aquatic plants on the community composition of Ostracoda in the upper Paraná River floodplain. We tested the hypothesis that non-swimming and small-sized species have a higher association with more complex plants by a threshold indicator taxa analysis. Some small and non-swimming ostracod species had a significant affinity for macrophytes with higher complexity, especially Eichhornia crassipes. However, most species did not show an association with the structure of aquatic macrophytes, and there was only a slightly distinction among the communities of different plants. The results show that structural complexity is in some cases an important determining factor for the community composition of Ostracoda, but other factors may interact with and even override the effects of complexity. It can thus be concluded that the relation between habitat complexity and the Ostracoda community composition is complex and not always responds to general predictions.

On Paranacypris samambaiensis gen. nov., sp. nov. (Crustacea, Ostracoda), the first South American psychrodromid from the alluvial valley of the Upper Paraná River, Brazil

Paranacypris samambaiensis gen. nov., sp. nov. is here described from closed lakes in the alluvial valley of the Upper Paraná River. The new genus, characterized by a large frontally overlapping left valve, belongs in the Psychrodromini, and is the first representative of this tribe described in South America. Nevertheless, it has some different character states, and the diagnosis of the tribe had to be adapted. The species is rare and restricted to closed lakes (not in contact with the main channels of the river). It mostly occurs in benthic littoral habitats, and far less in the pleuston communities, the most common habitat in this floodplain. The behaviour of P. samambaiensis gen. nov., sp. nov. is enigmatic because it combines long natatory setae on the antennae (swimming behaviour) with a very stout caudal ramus, including the spine‐like posterior seta (crawling behaviour). We present a key to the genera of the Herpetocypridinae.

Invasive South American floating plants are a successful substrate for native Central African pleuston

Eichhornia crassipes, commonly known as water hyacinth, is a free-floating perennial aquatic plant native to South America, which has been widely introduced on different continents, including Africa. E. crassipes is abundant in both the Congo (Africa) and Amazon (South America) River catchments. We performed a comparative analysis of the ostracod communities (Crustacea, Ostracoda) in the E. crassipes pleuston in the Amazon (South America) and Congo (Africa) River catchments. We also compared the ostracod communities from the invasive E. crassipes with those associated with stands of the native African macrophyte Vossia cuspidata. We recorded 25 species of ostracods associated with E. crassipes in the Amazon and 40 in the Congo River catchments, distributed over 31 ostracod species in E. crassipes and 27 in V. cuspidata. No South American invasive ostracod species were found in the Congolese pleuston. Diversity and richness of Congolese ostracod communities was higher in the invasive (Eichhornia) than in a native plant (Vossia). The highest diversity and abundance of ostracod communities were recorded in the Congo River. The result of principal coordinates analysis, used to evaluate the (dis)similarity between different catchments, showed significant differences in species composition of the communities. However, a dispersion homogeneity test (PERMDISP) showed no significant differences in the variability of the composition of species of ostracods (beta diversity) within Congo and Amazon River catchments. It appears that local ostracod faunas have adapted to exploit the opportunities presented by the floating invasive Eichhornia, which did not act as “Noah’s Ark” by introducing South American ostracods in the Congo River.

Diversity of ostracod communities (Crustacea, Ostracoda) across hierarchical spatial levels in a tropical floodplain

Assessing and evaluating the mechanism and patterns of species distribution across multiple hierarchical spatial levels, such as in floodplains, are important for understanding the factors that influence the structure of communities. The species composition may vary at these spatial levels or between the spatial levels along the hierarchical scale. Thus, using the additive partitioning in species richness, Shannon index, and Simpson coefficient, we tested the hypothesis that the alpha and beta components of ostracod diversity are unevenly distributed along the hierarchical spatial levels in the Upper Paraná River floodplain (Brazil). The results obtained by PCoA and diversity partitioning allowed us to conclude that dispersal is efficient, and that at higher spatial levels (floodplain, systems, and environments), the establishment of a new population of ostracods depends on both abiotic and biotic factors. However, at lower levels, spatial factors such as plants architecture and other biotic factors, e.g., competition, may have greater influence on community structure.

Caloric Variability of Corbicula fluminea (Mollusca, Bivalvia) in Rosana Reservoir, Brazil

The purpose of the present study was to investigate temporal and longitudinal variation of caloric density of Corbicula fluminea in Rosana Reservoir. Significant differences concerning the caloric density of C. fluminea were observed throughout the year at the three reservoir sites. The caloric density variation during the year was probably related to reproductive activity, which demanded higher allocation of energy in certain period. The food source used by this species might be an important factor in the caloric value temporal and spatial variation of C. fluminea in Rosana Reservoir.