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, Paraná 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.

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.

The complexity of the relations between the organisms and the environment are reflected through the energy content. So we tested the hypothesis on body energy content variation in invertebrates and its relation with some environmental factors (season, habitat type, trophic status and trophic guild). We expected higher energy values for phytophilous fauna, rainy season, in reservoirs with higher trophic levels and for herbivorous invertebrates. The results showed the influence of seasonality and trophic status of the reservoir on the energy content of invertebrates, which was higher in the rainy season and in the mesotrophic reservoirs, due to the input of allochthonous material during this season, confirming our initial prediction. A higher caloric content was recorded for carnivorous and detritivorous invertebrates. The differences between the trophic guilds were primarily related to the opportunistic feeding behavior, which may be considered as one of the main factors controlling the energy flow of benthic and phytophilous invertebrates. IntroductionThe energy dynamics in aquatic ecosystems can be better understood by studying the caloric content of the organisms (MUNN and BRUSVEN, 1991). However, the small size of aquatic invertebrates is often a problem for obtaining energy measurements, mainly due to the difficulty of sampling a large number of small specimens needed for calorimeter measurements (FELLER and WARWICK, 1988;LUCAS, 1992). Several studies have improved the knowledge on the energy content of several organisms.Since the pioneer work of LINDEMAN`s (1942) about the energy availability and trophic chains, several research projects were carried out in aquatic marine and freshwater ecosystems of temperate regions. A study performed by WISSING and HASSLER (1971) in freshwater ecosystems showed that the caloric values of invertebrates were related to seasonal variations. For example, the energetic content of Chironomidae was higher in the summer, because this is the growing season and quickly declined in the winter. STANCZYKOWSKA and LAWACZ (1976) also recorded higher energy value of Dreissena polymorpha in summer. Several others studies have stressed the importance of energy measures for the understand- ing of the dynamics of aquatic ecosystems (GOLLEY, 1961;CUMMINS and WUYCHECK, 1971; DRIVER et al., 1974;SALONEN et al., 1976;CLARKE et al., 1985;DAUVIN and JONCOURT, 1989;BEUKEMA, 1997;DOYLE et al., 2007). Nevertheless, even in well-studied temperate regions, the knowledge of the caloric content is still incomplete for many organisms (DOYLE et al., 2007).In Neotropical aquatic ecosystems, few studies have thus far investigated the caloric content, so data on the energy content of organisms in these ecosystems is even more scarce and mostly restricted to ichthyofauna (NGAN et al., 1993;DORIA and ANDRIAN, 1997;BENEDITO-CECILIO et al., 2004;SANTANA et al., 2005;ESPÍNOLA et al., 2008), aquatic macrophytes (ESTEVES and THOMAZ, 1990;DOURADO et al., 2004;LOPES et al., 2006) and a few invertebrate group...

ABSTRACT. The purpose of the present study was to verify, using RAPD and ISSR molecular techniques associated with the morphological characterization of bivalve shells, if the morphologically distinct specimens of Corbicula fluminea sampled at Rosana Reservoir belong to different species. The foot muscle tissue of the three groups (G1, G2, and G3) of Corbicula was removed and frozen in liquid nitrogen to the DNA analyze. Morphometric variables of the shell indicated significant differences among the specimens of Corbicula. On the other hand, molecular analyses revealed genetic similarity among the specimens, showing the nonexistence of molecular polymorphism. The data confirmed that the two morphologically different groups also belong to the species C. fluminea, showing the occurrence of phenotypic plasticity, probably caused by environmental or biotic factors.Key words: Corbicula, molecular techniques, phenotypic plasticity, environmental variation.RESUMO. Caracterização morfológica e molecular de Corbicula (Mollusca, Bivalvia) no reservatório de Rosana, Brasil. O objetivo do presente estudo foi verificar através de técnicas moleculares, RAPD e ISSR aliadas à caracterização morfológica da concha dos bivalves, se os indivíduos morfologicamente distintos de Corbicula fluminea amostrados no reservatório de Rosana pertencem a espécies diferentes. O tecido muscular do pé dos três grupos (G1, G2 e G3) de Corbicula foi removido e congelado em nitrogênio líquido para a análise do DNA. As variáveis morfométricas das conchas indicaram diferenças significativas entre os indivíduos de Corbicula. Por outro lado, as análises moleculares revelaram similaridade genética, evidenciando a não existência de polimorfismo molecular. Os resultados confirmam que os dois grupos diferentes morfologicamente também pertencem a espécie C. fluminea, demonstrando a ocorrência de plasticidade fenotípica, provavelmente causada por fatores bióticos ou ambientais.Palavras-chave: Corbicula, técnicas moleculares, plasticidade fenotípica, variação ambiental.