Dams are a major threat to aquatic biological diversity. By altering the natural flow of rivers, dams modify fluvial habitats, making them unsuitable for the growth and reproduction of many aquatic species. The aim of this study was to evaluate the effects of a reduced flow reach (RFR) on benthic macroinvertebrate communities. Benthic macroinvertebrates were collected at six sites downstream of the Amador Aguiar Power Plant I before (lotic phase) and after (semi-lentic phase) Araguari River mean flow was reduced from 346 to 7 m 3 .s -1. Changes in macroinvertebrates richness, diversity and total biomass were not observed. Ablabesmyia, Tanytarsus (Chironomidae, Diptera), Leptoceridae and Polycentropodidae (Trichoptera) densities significantly increased the first year after flow reduction and the construction of spillways (t-test; p < 0.05). An analysis of similarity (ANOSIM) showed statistical differences in taxonomical composition despite considerable overlap in communities between the lotic and semi-lentic phases (R = 0.3; p < 0.01). In both phases, the macroinvertebrates were characterised by the dominance of groups tolerant to human disturbance (e.g., Chironomidae, Ceratopogonidae and Oligochaeta) and by the presence of the alien bivalve species Corbicula fluminea (Veneroidae), suggesting that the river was already degraded before the hydraulic modifications. Since the 1980s, the Araguari River has been continuously subjected to human pressures (e.g., cascade dams, urbanization and replacement of native vegetation by pasture and crops). These activities have led to impoverishment of biological communities and have consequently altered the ecosystem.Keywords: spillways, reduced flow, dams, benthic, anthrophic impacts.Efeitos da redução de vazão e construção de soleiras vertentes sobre a composição e estrutura de comunidades de macroinvertebrados bentônicos em um trecho de rio brasileiro ResumoAs represas constituem uma das principais ameaças à diversidade biológica. Ao alterarem a vazão natural de um rio, modificam os habitats fluviais tornando-os inadequados para o crescimento e reprodução de diversas espécies aquáticas. O objetivo deste estudo foi avaliar os efeitos de um trecho de vazão reduzida sobre as comunidades de macroinvertebrados bentônicos. Os organismos foram coletados em seis estações amostrais à jusante da UHE Amador Aguiar I antes (fase lótica) e após (fase semilêntica) a vazão média do rio Araguari (MG) ter sido reduzida de 346 para 7 m 3 .s -1. Não foram registradas mudanças na riqueza, diversidade e biomassa total dos macroinvertebrados. As densidades (ind.m -2 ) de Ablabesmyia, Tanytarsus (Diptera), Leptoceridae e Polycentropodidae (Trichoptera) aumentaram significativamente no primeiro ano após a redução da vazão e construção das soleiras vertentes (t-test; p < 0,05). Uma análise de similaridade (ANOSIM) apontou diferenças significativas na composição taxonômica, porém houve sobreposição das comunidades entre as fases lótica e semilêntica (R = 0,3; p < 0,01). Em ambas as fases a ma...
Fusarium verticillioides is a primary corn pathogen and one of the main producers of fumonisins, a group of mycotoxins that cause several diseases in animals and probably also affect humans. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on polyclonal antibodies was developed to detect the exoantigen of this fungus in corn and its correlation with traditional methods for mould detection was evaluated. Forty freshly harvested corn samples were analysed for F. verticillioides exoantigens, as well as for total mould count, ergosterol and fumonisin levels in order to evaluate the relationship between these parameters. In addition, F. verticillioides was grown in brain heart infusion (BHI) broth in order to evaluate the correlation between biomass and exoantigen concentration. There was no significant correlation between exoantigen concentration and total mould count, Fusarium sp. count and fumonisin levels. The correlation coefficient between exoantigens and ergosterol content was 0.52 and between biomass and F. verticillioides exoantigens in BHI broth was 0.84. These results suggest that this ic-ELISA has potential for Fusarium sp. detection in corn samples.
The effect of different concentrations of aqueous extracts of Melia azedarach on Spodoptera frugiperda biology was investigated under laboratory conditions. Corn leaves were immersed in solutions with extract concentrations of 0.1%; 1.0% and 5.0% and offered to newly-born larvae. At higher doses (1.0% and 5.0%) the extracts caused 100 % mortality of larvae. Observations of dead larvae showed abnormal moults and death at ecdysis. At the concentration of 0.1%, chinaberry extract increased the larval phase and reduced significantly the larval and pupal weight. Reproduction parameters, as the number of eggs per female, eggs per oviposition and eggs viability were affected using emerged adults from treated larvae with concentration of 0.1% Melia extract. The fecundity was drastically reduced. Survival and duration of egg stage were not affected by the extracts. No effect was observed in relation to attractiveness of caterpillars at first instar in tests with possibility of choice. The chinaberry aqueous extract showed good potential to be used as a control agent for S. frugiperda.
Behavioral responses are important in zooplankton species exposed to invertebrate predators. In a Brazilian natural lake, the ostracod Physocypria schubarti Farkas, 1958 is abundant, despite the presence of predatory Chaoborus Lichtenstein, 1800 larvae. This is intriguing as this predator controls several microcrustacean populations in nature. Therefore, we analysed the interactions between fourth instar Chaoborus larvae and ostracods of two body sizes in laboratory. We evaluated (1) the behaviour of P. schubarti during Chaoborus attacks, (2) the probability of Chaoborus larvae ingesting them during such interactions and (3) the prey survival and predator ingestion rates after 24 h. When attacked, ostracods of both sizes frequently ceased to move and passively sank in the water column. This anti-predation strategy (“akinesis” or “dead-man response”) was observed in over 80% of the interactions involving physical contact. Surprisingly the probability of Chaoborus larvae eating prey that exhibited, or not, this reaction was close or equal to zero. After 24 h, over 92% of the prey survived and the ingestion rate of the chaoborids was practically nihil. Our results suggest that, although akinesis is a very common behaviour, additional features of P. schubarti may be as or more important in explaining its low vulnerability when in high spatial overlap with Chaoborus larvae.
Although it is well known that predatory Chaoborus Lichtenstein 1800 larvae have a strong negative impact on zooplankton populations in many Holarctic lakes, this top‐down control is still not entirely clear in the Neotropics. In Lake Carioca, a Brazilian monomictic lake, chaoborids became one of the main zooplankton predators after the depletion of planktivorous fish by non‐native piscivorous fish. The aim of this research was to test the hypothesis that Chaoborus spp. larvae control the density of their prey populations. Enclosures simulated conditions with higher (Pr+) and lower (Pr−) predatory Chaoborus spp. larva densities over 30 days in two periods (stratification and mixing). Our results indicated that the dominant copepod species was affected only in the stratification period when its population was smaller. In this circumstance, predated individuals were probably not replaced in the same proportion by reproductive output of the smaller population. Rotifers were not sensitive to changes in chaoborids densities in both periods. The lack of a strong top‐down effect recorded by our mesocosm experiments emphasises the importance of continuing to investigate the ecological roles played by this invertebrate predator in aquatic food webs and if its ability to regulate the zooplankton in most Holarctic lakes can (or cannot) be widely generalised to Neotropical communities. Such a result also suggests that alternative research approaches, besides in‐situ experiments, may be necessary to better clarify this topic. Specifically for cladocerans, parallel paleolimnological analyses in Lake Carioca have supported the idea of a possible negative impact of Chaoborus larvae on bosminids after the introduction of non‐native piscivorous fishes.Abstract in Portuguese is available with online material.
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