Exploring dose-response relationships in Aedes aegypti survival upon bacteria and arbovirus infection.

A detailed understanding of how host fitness changes in response to variations in microbe density (an ecological measure of disease tolerance) is an important aim of infection biology. Here, we applied dose-response curves to study Aedes aegypti survival upon exposure to different microbes. We challenged female mosquitoes with Listeria monocytogenes, a model bacterial pathogen, Dengue 4 virus and Zika virus, two medically relevant arboviruses, to understand the distribution of mosquito survival following microbe exposure. By correlating microbe loads and host health, we found that a blood meal promotes disease tolerance in our systemic bacterial infection model and that mosquitoes orally infected with bacteria had an enhanced defensive capacity than insects infected through injection. We also showed that Aedes aegypti displays a higher survival profile following arbovirus infection when compared to bacterial infections. Here, we applied a framework for investigating microbe-induced mosquito mortality and details how the lifespan of Aedes aegypti varies with different inoculum sizes of bacteria and arboviruses.

Human land-uses homogenize stream assemblages and reduce animal biomass production.

Human land-use change is a major threat to natural ecosystems worldwide. Nonetheless, the effects of human land-uses on the structure of plant and animal assemblages and their functional characteristics need to be better understood. Furthermore, the pathways by which human land uses affect ecosystem functions, such as biomass production, still need to be clarified. We compiled a unique dataset of fish, arthropod and macrophyte assemblages from 61 stream ecosystems in two Neotropical biomes: Amazonian rainforest and Uruguayan grasslands. We then tested how the cover of agriculture, pasture, urbanization and afforestation affected the taxonomic richness and functional diversity of those three species assemblages, and the consequences of these effects for animal biomass production. Single trait categories and functional diversity were evaluated, combining recruitment and life-history, resource and habitat-use, and body size. The effects of intensive human land-uses on taxonomic and functional diversities were as strong as other drivers known to affect biodiversity, such as local climate and environmental factors. In both biomes, the taxonomic richness and functional diversity of animal and macrophyte assemblages decreased with increasing cover of agriculture, pasture, and urbanization. Human land-uses were associated with functional homogenization of both animal and macrophyte assemblages. Human land-uses reduced animal biomass through direct and indirect pathways mediated by declines in taxonomic and functional diversities. Our findings indicate that converting natural ecosystems to supply human demands results in species loss and trait homogenization across multiple biotic assemblages, ultimately reducing animal biomass production in streams.

Engineering graphene-based electrodes for optical neural stimulation.

Graphene-based materials (GBMs) have been investigated in recent years with the aim of developing flexible interfaces to address a range of neurological disorders, where electrical stimulation may improve brain function and tissue regeneration. The recent discovery that GBM electrodes can generate an electrical response upon light exposure has inspired the development of non-genetic approaches capable of selectively modulating brain cells without genetic manipulation (i.e., optogenetics). Here, we propose the conjugation of graphene with upconversion nanoparticles (UCNPs), which enable wireless transcranial activation using tissue-penetrating near-infrared (NIR) radiation. Following a design of experiments approach, we first investigated the influence of different host matrices and dopants commonly used to synthesize UCNPs in the electrical response of graphene. Two UCNP formulations achieving optimal enhancement of electrical conductivity upon NIR activation at λ = 780 or 980 nm were identified. These formulations were then covalently attached to graphene nanoplatelets following selective hydroxyl derivatization. The resulting nanocomposites were evaluated in vitro using SH-SY5Y human neuroblastoma cells. NIR activation at λ = 980 nm promoted cell proliferation and downregulated neuronal and glial differentiation markers, suggesting the potential application of GBMs in minimally invasive stimulation of cells for tissue regeneration.

Regime shifts in a shallow lake over 12 years: Consequences for taxonomic and functional diversities, and ecosystem multifunctionality.

Under increasing nutrient loading, shallow lakes may shift from a state of clear water dominated by submerged macrophytes to a turbid state dominated by phytoplankton or a shaded state dominated by floating macrophytes. How such regime shifts mediate the relationship between taxonomic and functional diversities (FD) and lake multifunctionality is poorly understood. We employed a detailed database describing a shallow lake over a 12-year period during which the lake has displayed all the three states (clear, turbid and shaded) to investigate how species richness, FD of fish and zooplankton, ecosystem multifunctionality and five individual ecosystem functions (nitrogen and phosphorus concentrations, standing fish biomass, algae production and light availability) differ among states. We also evaluated how the relationship between biodiversity (species richness and FD) and multifunctionality is affected by regime shifts. We showed that species richness and the FD of fish and zooplankton were highest during the clear state. The clear state also maintained the highest values of multifunctionality as well as standing fish biomass production, algae biomass and light availability, whereas the turbid and shaded states had higher nutrient concentrations. Functional diversity was the best predictor of multifunctionality. The relationship between FD and multifunctionality was strongly positive during the clear state, but such relationship became flatter after the shift to the turbid or shaded state. Our findings illustrate that focusing on functional traits may provide a more mechanistic understanding of how regime shifts affect biodiversity and the consequences for ecosystem functioning. Regime shifts towards a turbid or shaded state negatively affect the taxonomic diversity and FD of fish and zooplankton, which in turn impairs the multifunctionality of shallow lakes.

Ontogenetic diet shifts: an additional mechanism for successful invasion of a piranha species in a Neotropical floodplain.

Ontogenetic shifts in food preference reduces intraspecific competition as immature individuals eat different food types than adults. This diet plasticity could facilitate species' ability to successfully invade and establish itself in a new environment, even when co-occurring with phylogenetically close species. Here, ontogenetic diet shifts of a non-native piranha species (Serrasalmus marginatus) was tested by analyzing the relationship between its body length and the carbon and nitrogen stable isotope signatures. Carbon stable isotope was not correlated to fish length, but positive significant correlation between δ15N values and fish length was found for the non-native piranha. Also, immature and adult S. marginatus showed low isotopic niche overlap. The correlation between fish length and δ15N, and the low trophic overlap between immature and adult, indicate that the non-native S. marginatus had ontogenetic shifts in food preference, which may be viewed as an additional mechanism underlying its successful establishment in the upper Paraná River. Our findings indicate that ontogenetic shifts in food preference may be an invasive trait that facilitates the establishment of non-native fish species in tropical aquatic systems.

Negative effect of turbidity on prey capture for both visual and non-visual aquatic predators.

Turbidity plays an important role in aquatic predator-prey interactions. Increases in turbidity are expected to reduce prey capture rates, especially for visually oriented predators. However, there is also evidence indicating that turbidity may have little or no effect on predation rates. Here, we conducted a systematic review and meta-analysis of the relationship between turbidity and capture rate. We explored possible sources of heterogeneity in the effect sizes (capture strategy, predator's body size, relative eye size and turbidity range in the experiments) while controlling for the dependence among effects sizes and phylogenetic relationships among predator species. We found a consistent negative effect of turbidity on prey capture and that turbidity range (manipulated in the experiments) was the main factor accounting for between-study variation in effect sizes. Also, capture rates of both visually and non-visually oriented predators decreased with an increase in turbidity. In addition, for visually oriented fish predators, the relative eye size did not influence the effect sizes. Despite the paucity of studies for some groups of aquatic predators (mainly in tropical regions), we provide corroborative evidence that turbidity is a critical environmental factor controlling predator-prey interactions. This result is especially relevant considering that changes in turbidity is a human-induced pervasive environmental alteration resulted from, among other mechanisms, runoff after deforestation, eutrophication or oligotrophication in reservoir cascades, which imply changes in predator-prey interactions.

Fire increases the productivity of sugarcane, but it also generates ashes that negatively affect native fish species in aquatic systems.

Sugarcane is one of the main crops used around the world as a feedstock for the production of sucrose and biofuel. Prior to harvesting, sugarcane dry leaves are burned to facilitate manual cutting and enhance productivity. This practice generates ashes from sugarcane straw (hereafter referred as SCA), which may be carried to aquatic ecosystems, where its impacts on organisms and ecosystem integrity remain unknown. Here, we experimentally tested the toxicity of five different concentrations of SCA (0, 1000, 1500, 2000 and 2500 mg/L) on three native (Astyanax lacustris, Moenkhausia bonita and M. forestii) and two non-native (Oreochromis niloticus and Poecilia reticulata) fish from the Paraná River Basin, Brazil. The toxicity was estimated by calculating the median lethal concentration (LC50-24h) and the hepatosomatic index (HSI). We hypothesised that native fish are more sensitive to an increase in SCA than non-native fish. We verified that the mortality of native fish sharply increased with the increase in higher SCA concentration (LC50-24h values: A. lacustris = 2525.71 mg/L, M. bonita = 2124.95 mg/L and M. forestii = 1981.74 mg/L). However, no deaths were recorded for non-native fish species in any SCA concentrations. Accordingly, the HSI index values statistically differed with the increase in SCA concentrations for native fish, while for non-native fish we did not observe any difference. Therefore, only native species died or suffered liver damage with an increase in SCA concentrations. Extrapolating our findings to natural environments, we suggest that sugarcane burning, a widely used agricultural technique, has the potential to reduce the population size of native organisms and facilitate the dominance of non-native fish species in aquatic ecosystems.

Misguided policy may jeopardize a diverse South brazilian environmental protection area / Política equivocada pode colocar em risco uma área de preservação ambiental do sul do Brasil

Abstract: The Devonian Escarpment (DEEPA), located in the south of Brazil, represents an important area of environmental preservation composed by grasslands, gallery forests, as well as rock outcrops and archaeological sites. A law project (LP 527/2016), which suggests a reduction of the DEEPA area in approximately 70% of its original area (from 393,579 to 125,895 ha), is currently being processed in the Paraná State House of Representatives. Such reduction seems to be related to economic interests (mainly agriculture and mining) in the state of Paraná. If approved, LP 527/2016 will allow farmers to deliberately expand their activities, with the suppression of natural forest as main consequence. Additionally, loss of faunal diversity, contamination of water and soils, and alteration in nutrient cycles are expected, due the intensive use of agrochemicals. In addition to the direct environmental consequences, we expect the disappearance of areas of high geological interest, reducing local geodiversity, as well as substantial economic losses with ecotourism. Brazil is a signatory to the United Nations Convention on Biological Diversity, where it undertakes to develop strategies to prevent biodiversity loss and ecosystem degradation by 2020. An approval of the LP would be contradictory, considering that there are few natural vegetation areas in this region of the country. We emphasize that the proposal of such projects goes against the sustainability in the country and disregard the scientific knowledge generated until then. Thus, it is necessary to develop regional and federal political objectives that guarantee economic development in a balanced way, considering the local bio and geodiversity, not the proposal of mechanisms that destroy them.

Resumo: A Escarpa Devoniana (APAED), localizada no sul do Brasil, representa uma importante área de preservação ambiental composta por campos, matas de galeria, além de afloramentos rochosos e sítios arqueológicos. Atualmente, tramita na câmara dos deputados do estado do Paraná um projeto de lei estadual (PL 527/2016) que sugere a redução da área da APAED em aproximadamente 70% de sua área original (de 393.579 para 125.895 ha). Tal redução parece estar relacionada com interesses econômicos (principalmente agropecuária e mineração) no estado do Paraná. Caso aprovado, o PL 527/2016 permitirá que agricultores expandam suas atividades deliberadamente, tendo como consequência principal a supressão de áreas de floresta nativa. Com isso, espera-se perda de diversidade faunística, contaminação de água e solos e alteração nos ciclos de nutrientes, dado o aumento no uso de agroquímicos. Além das consequências ambientas diretas, podemos esperar o desaparecimento de elevado interesse geológico, reduzindo a geodiversidade local, além de substanciais perdas econômicas com ecoturismo. O Brasil é um dos países signatários da Convenção da Diversidade Biológica das Nações Unidas, onde se compromete a desenvolver estratégias que evitem a perda da biodiversidade e a degradação de ecossistemas até 2020. Assim, a aprovação desse projeto de lei é, no mínimo, contraditória considerando que existem poucas áreas de vegetação natural nessa região do país. Destacamos que a proposta de tais projetos vai contra a sustentabilidade no país e desconsideram o conhecimento científico gerado até então. Dessa forma, é necessário o desenvolvimento de objetivos políticos regionais e federais que garantam o desenvolvimento econômico de forma equilibrada, considerando a bio e geodiversidade local, e não a proposta de mecanismos que as destruam.

Food resources used by three species of fish in the semi-arid region of Brazil

Temporary and semi-permanent aquatic habitats in semi-arid Brazil have been reported as important sites supporting a diverse fish fauna. As such, they must be able to trophically sustain fish species that feed at different trophic levels. This study aims to describe the diets of Astyanax aff. bimaculatus, Hoplias malabaricus and Prochilodus brevis in aquatic systems in semi-arid Brazil, providing evidence of the importance of these habitats as supporters of large consumers like fish. The diet of the three species studied was diverse, feeding on a range of food items, from microalgae to fish. Despite that, a few items were more important to each of the study species. These results and the relatively high rates of stomach fullness indicate that a diverse and abundant food range is available in the study sites, but species seem to select some food resources. The present study provides evidence that despite being highly variable, intermittent and semi-permanent aquatic systems in semi-arid Brazil are able to trophically sustain large consumers.

Os ambientes aquáticos temporários e semi-permanentes do semiárido brasileiro tem sido mostrados como importantes sítios que possuem uma diversa fauna de peixes. Desta forma, esses ambientes devem ser capazes de sustentar, do ponto de vista trófico, populações de peixes que se alimentam em diversos níveis tróficos. O presente estudo tem como objetivo descrever o hábito alimentar de Astyanax aff. bimaculatus, Hoplias malabaricus e Prochilodus brevis em ambientes aquáticos do semiárido brasileiro, fornecendo evidências da importância desses habitats para manutenção da diversidade de consumidores como os peixes. A composição da dieta das espécies estudadas foi diversificada, já que alimentaram-se de uma variedade de classes de itens, desde microalgas até peixes. Apesar disso, alguns itens foram mais importantes para cada uma das três espécies. Estes resultados, e as altas taxas de repleção dos estômagos, indicam que um abundante e diverso conjunto de itens alimentares está disponível nos ambientes estudados, embora as espécies tendam a selecionar alguns itens em detrimento de outros. Este estudo fornece evidência de que, apesar de altamente variáveis, sistemas aquáticos intermitentes e semi-permanentes do semiárido brasileiro são capazes de sustentar, do ponto de vista trófico, consumidores de topo.