Hunting pressure modulates the composition and size structure of terrestrial and arboreal vertebrates in Amazonian forests

Overhunting is a leading contemporary driver of tropical forest wildlife loss. The absence or extremely low densities of large-bodied vertebrates disrupts plant-animal mutualisms and consequently degrades key ecosystem services. Understanding patterns of defaunation is therefore crucial given that most tropical forests worldwide are now “half-empty”. Here we investigate changes in vertebrate community composition and size structure along a gradient of marked anthropogenic hunting pressure in the Médio Juruá region of western Brazilian Amazonia. Using a novel camera trapping grid design deployed both in the understorey and the forest canopy, we estimated the aggregate biomass of several functional groups of terrestrial and arboreal species at 28 sites along the hunting gradient. Generalized linear models (GLMs) identified hunting pressure as the most important driver of aggregate biomass for game, terrestrial, and arboreal species, as well as nocturnal rodents, frugivores, and granivores. Local hunting pressure affected vertebrate community structure as shown by both GLM and ordination analyses. The size structure of vertebrate fauna changed in heavily hunted areas due to population declines in large-bodied species and apparent compensatory increases in nocturnal rodents. Our study shows markedly altered vertebrate community structure even in remote but heavily settled areas of continuous primary forest. Depletion of frugivore and granivore populations, and concomitant density-compensation by seed predators, likely affect forest regeneration in persistently overhunted tropical forests. These findings contribute to a better understanding of how cascading effects induced by historical defaunation operate, informing wildlife management policy in tropical peri-urban, rural and wilderness areas.

     

Pseudomonas aeruginosa–induced nociceptor activation increases susceptibility to infection

We report a rapid reduction in blink reflexes during in vivo ocular Pseudomonas aeruginosa infection, which is commonly attributed and indicative of functional neuronal damage. Sensory neurons derived in vitro from trigeminal ganglia (TG) were able to directly respond to P. aeruginosa but reacted significantly less to strains of P. aeruginosa that lacked virulence factors such as pili, flagella, or a type III secretion system. These observations led us to explore the impact of neurons on the host’s susceptibility to P. aeruginosa keratitis. Mice were treated with Resiniferatoxin (RTX), a potent activator of Transient Receptor Potential Vanilloid 1 (TRPV1) channels, which significantly ablated corneal sensory neurons, exhibited delayed disease progression that was exemplified with decreased bacterial corneal burdens and altered neutrophil trafficking. Sensitization to disease was due to the increased frequencies of CGRP-induced ICAM-1⁺ neutrophils in the infected corneas and reduced neutrophil bactericidal activities. These data showed that sensory neurons regulate corneal neutrophil responses in a tissue-specific matter affecting disease progression during P. aeruginosa keratitis. Hence, therapeutic modalities that control nociception could beneficially impact anti-infective therapy.     

Serum induces the immediate opening of Ca2+-activated channels in quiescent human fibroblasts

Application of fetal calf serum to quiescent human fibroblasts produces an immediate (3-20 s delay) increase in membrane conductance which lasts about 20-30 s. This conductance is strongly outwardly-rectifying and has a reversal potential between -45 and -10 mV. The conductance increase may also be induced by application of the Ca2+ ionophore A23187 while it does not occur when intracellular K+ is replaced by Cs+. It is concluded that this early effect of serum is due to the opening of Ca2+-activated channels. This permeability change will alter the membrane potential and thus possibly interact with other voltage-sensitive processes induced by serum growth factors.     

Environmental and Animal Characteristics as Factors Associated with American Cutaneous Leishmaniasis in Rural Locations with Presence of Dogs,Brazil

The aim of the study was to investigate the importance of dogs, other domesticated animals and environmental characteristics as risk factors in the epidemiology of American cutaneous leishmaniasis (ACL). A retrospective survey of cases of human ACL in the last ten years and visits to homes in rural locations were carried out in the municipality of Arapongas (southern Brazil) from 2008 to 2010. ACL in humans was significantly associated with a distance of up to 25 meters from the residence to a forest area (OR 5.08; 95% CI: 1.35–21.04), undergrowth area (OR 6.80; 95% CI: 1.69–45.33) and stream (OR 5.87; 95% CI: 1.15–24.59); banana plants near the residence (OR 5.98; 95% CI: 1.49–39.84), absence of ceiling below the roof in the residence (OR 7.30; 95% CI: 1.26–158.1), the dumping of trash in the forest area (OR 26.33; 95% CI: 7.32–93.46) and presence of ACL in dogs in the surrounding area (OR 4.39; 95% CI: 1.37–13.45). In dogs, ACL was associated with a distance of 25 to 50 meters and 51 to 100 meters, respectively, from the residence to a forest area (OR 2.59; 95% CI: 1.08–5.98; OR 3.29; 95% CI: 1.64–6.62), the presence of a stream up to 25 m from the residence (OR 6.23; 95% CI: 2.34–16.54) and banana plants near the residence (OR 0.45; 95% CI: 0.25–0.80). In the locations studied in the municipality of Arapongas (Brazil), the results reveal that canine infection increases the risk of human infection by ACL and the characteristics surrounding the residence increase the risk of infection in both humans and dogs. Thus, integrated environmental management could be a useful measure to avoid contact between humans and phlebotomines.     

Pore Hydration States of KcsA Potassium Channels in Membranes

Water-filled hydrophobic cavities in channel proteins serve as gateways for transfer of ions across membranes, but their properties are largely unknown. We determined water distributions along the conduction pores in two tetrameric channels embedded in lipid bilayers using neutron diffraction: potassium channel KcsA and the transmembrane domain of M2 protein of influenza A virus. For the KcsA channel in the closed state, the distribution of water is peaked in the middle of the membrane, showing water in the central cavity adjacent to the selectivity filter. This water is displaced by the channel blocker tetrabutyl-ammonium. The amount of water associated with the channel was quantified, using neutron diffraction and solid state NMR. In contrast, the M2 proton channel shows a V-shaped water profile across the membrane, with a narrow constriction at the center, like the hourglass shape of its internal surface. These two types of water distribution are therefore very different in their connectivity to the bulk water. The water and protein profiles determined here provide important evidence concerning conformation and hydration of channels in membranes and the potential role of pore hydration in channel gating.     

Human-Induced Trophic Cascades along the Fecal Detritus Pathway

Human presence and activity in tropical forest is thought to exert top-down regulation over the various ‘green-world’ pathways of plant-based foodwebs. However, these effects have never been explored for the ‘brown-world’ pathways of fecal-detritus webs. The strong effects of humans on tropical game mammals are likely to indirectly influence fecal detritivores (including Scarabaeine dung beetles), with subsequent indirect impacts on detrivore-mediated and plant-facilitating detrital processes. Across a 380-km gradient of human influence in the western Brazilian Amazon, we conducted the first landscape-level assessment of human-induced cascade effects on the fecal detritus pathway, by coupling data on human impact, game mammal and detritivore community structure, and rate measurements of a key detritus process (i.e. dung beetle-mediated secondary seed dispersal). We found evidence that human impact indirectly influences both the diversity and biomass of fecal detritivores, but not detritivore-mediated processes. Cascade strength varied across detritivore groups defined by species'' traits. We found smaller-bodied dung beetles were at higher risk of local decline in areas of human presence, and that body size was a better predictor of cascade structure than fecal resource manipulation strategy. Cascade strength was also stronger in upland, unflooded forests, than in seasonally flooded forests. Our results suggest that the impact of human activity in tropical forest on fecal-detritus food web structure is mediated by both species'' traits and habitat type. Further research will be required to determine the conditions under which these cascade effects influence fecal-detritus web function.     

Avian life-history determinants of local extinction risk in a hyper-fragmented neotropical forest landscape

The fact that species vary in their vulnerability to extinction is well documented, but the reasons for these differences remain poorly understood. Why should some species/families/guilds decline rapidly with increasing anthropogenic disturbance, while others either tolerate or proliferate in disturbed habitats? We investigated the bird species composition in 31 primary forest patches of varying size in a region of the Amazonian 'Arc of Deforestation' and assessed which species life-history traits predisposed individual species to extinction. Medium-sized non-flocking canopy frugivores/ominvores of low primary forest dependence were least likely to go extinct in small patches, while small-bodied flock-following primary-forest-dependent terrestrial insectivores were most fragmentation sensitive. We found highly idiosyncratic relationships between the minimum size of forest patches occupied by different species and their territory size requirements estimated based on other Amazonian studies. This suggests that avian assemblages in forest fragments primarily comprise species that either have good dispersal abilities or are highly tolerant to the non-forest matrix, rather than those whose minimum spatial requirements can be met by the size of available forest fragments.     

Impact of High-Fat Diet and Early Stress on Depressive-Like Behavior and Hippocampal Plasticity in Adult Male Rats

During development, the brain goes through fundamental processes, including organization of neural networks and plasticity. Environmental interventions may change initial brain programming, leading to long-lasting effects and altering the susceptibility to psychopathologies, including depression disorder. It is known that depression is a psychiatric disorder with a high prevalence worldwide, including high rates among adolescents. In this study, we evaluated whether social isolation in the prepubertal period and chronic use of high-fat diet (HFD) may induce depressive-like behavior in male adult rats. We also investigated hippocampal plasticity markers and neurotransmitter systems. We found both social isolation and HFD induced a depressive-like behavior in the forced swimming task. Moreover, chronic HFD reduced synaptic markers in hippocampus, demonstrated by reductions in βIII-tubulin (neuronal marker), PSD-95, SNAP-25, and neurotrophin-3. The HFD group also presented decreased glutamatergic and GABAergic receptors subunits. On the other hand, stress affected hippocampal brain-derived neurotrophic factor (BDNF) signaling pathways, and increased expression of subunit of the NMDA receptor (NR2A). Both factors (stress and diet) decreased GR in the hippocampus without affecting plasma corticosterone at basal levels. Interactions between early stress and HFD access were observed only in the BNDF receptor (tropomyosin receptor kinase B; TrkB) and synaptophysin. In summary, these findings showed that a brief social isolation and chronic HFD, during a sensitive developmental period, cause depressive-like behavior in adulthood. The mechanisms underlying these behavioral effects may involve changes in the levels of synaptic proteins in hippocampus: HFD consumption appears to affect synaptic markers, while social isolation affected BDNF signaling more significantly.