Forest structure in a mosaic of rainforest sites: The effect of fragmentation and recovery after clear cut

A variety of human-induced disturbances such as forest fragmentation and recovery after deforestation for pasture or agricultural activities have resulted in a complex landscape mosaic in the Una region of northeastern Brazil. Using a set of vegetation descriptors, we investigated the main structural changes observed in forest categories that comprise the major components of the regional landscape and searched for potential key descriptors that could be used to discriminate among different forest categories. We assessed the forest structure of five habitat categories defined as (I) interiors and (2) edges of large fragments of old-growth forest (>1000 ha), (3) interiors and (4) edges of small forest fragments (<100 ha), and (5) early secondary forests. Forest descriptors used here were: frequency of herbaceous lianas and woody climbers, number of standing dead trees, number of fallen trunks, litter depth, number of pioneer plants (early secondary and shade-intolerant species), vertical foliage stratification profile and distribution Of trees in different diameter classes. Edges and interiors of forest fragments were significantly different only in the number of standing dead trees. Secondary forests and edges of fragments showed differences in litter depth, fallen trunks and number of pioneer trees, and secondary forests were significantly different from fragment interiors in the number of standing dead trees and the number of pioneer trees. Horizontal and vertical structure evaluated via ordination analysis showed that fragment interiors, compared to secondary forests, were characterized by a greater number of medium (25-35 cm) and large (35-50 cm) trees and smaller numbers of thin trees (5-10 cm). There was great heterogeneity at the edges of small and large fragments, as these sites were distributed along almost the entire gradient. Most interiors of large and small fragments presented higher values of foliage densities at higher strata ( 15-20 m and at 20-25 m height), and lower densities at 1-5 m. All secondary forests and some fragment edge sites showed an opposite tendency. A discriminant function highlighted differences among forest categories, with transects of large fragment interiors and secondary forests representing two extremes along a disturbance gradient determined by foliage structure (densities at 15-20 m and 20-25 m), with the edges of both large and small fragments and the interiors of small fragments scattered across the gradient. The major underlying processes determining patterns of forest disturbance in the study region are discussed, highlighting the importance of forest fragments, independently of its size, as forests recovery after clear cut show a greatly distinct structure, with profound implications on fauna movements. (C) 2009 Elsevier BY. All rights reserved.

Analysis of a hyper-diverse seed dispersal network: modularity and underlying mechanisms

Mutualistic interactions involving pollination and ant-plant mutualistic networks typically feature tightly linked species grouped in modules. However, such modularity is infrequent in seed dispersal networks, presumably because research on those networks predominantly includes a single taxonomic animal group (e.g. birds). Herein, for the first time, we examine the pattern of interaction in a network that includes multiple taxonomic groups of seed dispersers, and the mechanisms underlying modularity. We found that the network was nested and modular, with five distinguishable modules. Our examination of the mechanisms underlying such modularity showed that plant and animal trait values were associated with specific modules but phylogenetic effect was limited. Thus, the pattern of interaction in this network is only partially explained by shared evolutionary history. We conclude that the observed modularity emerged by a combination of phylogenetic history and trait convergence of phylogenetically unrelated species, shaped by interactions with particular types of dispersal agents.

Local richness and distribution of the lizard fauna in natural habitat mosaics of the Brazilian Cerrado

We investigate local lizard richness and distribution in central Brazilian Cerrado, harbouring one of the least studied herpetofaunas in the Neotropical region. Our results are based on standardized samplings at 10 localities, involving 2917 captures of 57 lizard species in 10 families. Local richness values exceeded most presented in earlier studies and varied from 13 to 28 species, with modal values between 19 and 28 species. Most of the Cerrado lizard fauna is composed of habitat-specialists with patchy distributions in the mosaic of grasslands, savannas and forests, resulting in habitat-structured lizard assemblages. Faunal overlap between open and forested habitats is limited, and forested and open areas may act as mutual barriers to lizard distribution. Habitat use is influenced by niche conservatism in deep lineages, with iguanians and gekkotans showing higher use of forested habitats, whereas autarchoglossans are richer and more abundant in open habitats. Contrary to trends observed in Cerrado birds and large mammals, lizard richness is significantly higher in open, interfluvial habitats that dominate the Cerrado landscape. Between-localities variation in lizard richness seems tied to geographical distance, landscape history and phylogenetic constraints, factors operating in other well-studied lizard faunas in open environments. Higher richness in dominant, open interfluvial habitats may be recurrent in Squamata and other small-bodied vertebrates, posing a threat to conservation as these habitats are most vulnerable to the fast, widespread and ongoing process of habitat destruction in central Brazil.

Using gap-crossing capacity to evaluate functional connectivity of two Atlantic rainforest birds and their response to fragmentation

One of the main consequences of habitat loss and fragmentation is the increase in patch isolation and the consequent decrease in landscape connectivity. In this context, species persistence depends on their responses to this new landscape configuration, particularly on their capacity to move through the interhabitat matrix. Here, we aimed first to determine gap-crossing probabilities related to different gap widths for two forest birds (Thamnophilus caerulescens, Thamnophilidae, and Basileuterus culicivorus, Parulidae) from the Brazilian Atlantic rainforest. These values were defined with a playback technique and then used in analyses based on graph theory to determine functional connections among forest patches. Both species were capable of crossing forest gaps between patches, and these movements were related to gap width. The probability of crossing 40 m gaps was 50% for both species. This probability falls to 10% when the gaps are 60 m (for B. culicivorus) or 80 m (for T caerulescens). Actually, birds responded to stimulation about two times more distant inside forest trials (control) than in gap-crossing trials. Models that included gap-crossing capacity improved the explanatory power of species abundance variation in comparison to strictly structural models based merely on patch area and distance measurements. These results highlighted that even very simple functional connectivity measurements related to gap-crossing capacity can improve the understanding of the effect of habitat fragmentation on bird occurrence and abundance.

Are leaf-litter frogs and lizards affected by edge effects due to forest fragmentation in Brazilian Atlantic forest?

FAPESP Fundacao de Amparo a Pesquisa do Estado de Sao Paulo

The nested assembly of individual-resource networks

P>1. Much of the current understanding of ecological systems is based on theory that does not explicitly take into account individual variation within natural populations. However, individuals may show substantial variation in resource use. This variation in turn may be translated into topological properties of networks that depict interactions among individuals and the food resources they consume (individual-resource networks). 2. Different models derived from optimal diet theory (ODT) predict highly distinct patterns of trophic interactions at the individual level that should translate into distinct network topologies. As a consequence, individual-resource networks can be useful tools in revealing the incidence of different patterns of resource use by individuals and suggesting their mechanistic basis. 3. In the present study, using data from several dietary studies, we assembled individual-resource networks of 10 vertebrate species, previously reported to show interindividual diet variation, and used a network-based approach to investigate their structure. 4. We found significant nestedness, but no modularity, in all empirical networks, indicating that (i) these populations are composed of both opportunistic and selective individuals and (ii) the diets of the latter are ordered as predictable subsets of the diets of the more opportunistic individuals. 5. Nested patterns are a common feature of species networks, and our results extend its generality to trophic interactions at the individual level. This pattern is consistent with a recently proposed ODT model, in which individuals show similar rank preferences but differ in their acceptance rate for alternative resources. Our findings therefore suggest a common mechanism underlying interindividual variation in resource use in disparate taxa.

Fragmentation drives tropical forest fragments to early successional states: A modelling study for Brazilian Atlantic forests

Land use leads to massive habitat destruction and fragmentation in tropical forests. Despite its global dimensions the effects of fragmentation on ecosystem dynamics are not well understood due to the complexity of the problem. We present a simulation analysis performed by the individual-based model FORMIND. The model was applied to the Brazilian Atlantic Forest, one of the world`s biodiversity hot spots, at the Plateau of Sao Paulo. This study investigates the long-term effects of fragmentation processes on structure and dynamics of different sized remnant tropical forest fragments (1-100 ha) at community and plant functional type (PFT) level. We disentangle the interplay of single effects of different key fragmentation processes (edge mortality, increased mortality of large trees, local seed loss and external seed rain) using simulation experiments in a full factorial design. Our analysis reveals that particularly small forest fragments below 25 ha suffer substantial structural changes, biomass and biodiversity loss in the long term. At community level biomass is reduced up to 60%. Two thirds of the mid- and late-successional species groups, especially shade-tolerant (late successional climax) species groups are prone of extinction in small fragments. The shade-tolerant species groups were most strongly affected; its tree number was reduced more than 60% mainly by increased edge mortality. This process proved to be the most powerful of those investigated, explaining alone more than 80% of the changes observed for this group. External seed rain was able to compensate approximately 30% of the observed fragmentation effects for shade-tolerant species. Our results suggest that tropical forest fragments will suffer strong structural changes in the long term, leading to tree species impoverishment. They may reach a new equilibrium with a substantially reduced subset of the initial species pool, and are driven towards an earlier successional state. The natural regeneration potential of a landscape scattered with forest fragments appears to be limited, as external seed rain is not able to fully compensate for the observed fragmentation-induced changes. Our findings suggest basic recommendations for the management of fragmented tropical forest landscapes. (C) 2011 Elsevier B.V. All rights reserved.

Transport of animals between rooms: A little-noted aspect of laboratory procedure that may interfere with memory

This study investigated the effects of transporting animals from the experimental room to the animal facility in between experimental sessions, a procedure routinely employed in experimental research, on long-term social recognition memory. By using the intruder-resident paradigm, independent groups of Wistar rats exposed to a 2-h encounter with an adult intruder were transported from the experimental room to the animal facility either 0.5 or 6h after the encounter. The following day, residents were exposed to a second encounter with either the same or a different (unfamiliar) intruder. Resident`s social and non-social behaviors were carefully scored and subjected to Principal Component Analysis, thus allowing to parcel out variance and relatedness among these behaviors. Resident rats transported 6h after the first encounter exhibited reduced amount of social investigation towards familiar intruders, but an increase of social investigation when exposed to a different intruder as compared to the first encounter. These effects revealed a consistent long-lasting (24h) social recognition memory in rats. In contrast, resident rats transported 0.5 h after the first encounter did not exhibit social recognition memory. These results indicate that this common, little-noted, laboratory procedure disturbs long-term social recognition memory. (C) 2011 Elsevier B.V. All rights reserved.

Negative anticipatory contrast: Does it involve anticipation of an impending reward?

Negative anticipatory contrast (NAC) corresponds to the suppression in consumption of a first rewarding substance (e.g., saccharin 0.15%) when it is followed daily by a second preferred substance (e.g., sucrose 32%). The NAC has been interpreted as resulting from anticipation of the impending preferred reward and its comparison with the currently available first reward [Flaherty, CF., Rowan, G.A., 1985. Anticipatory contrast: within-subjects analysis. Anim. Learn. Behav. 13, 2-5]. In this context, one should expect that devaluation of the preferred substance after the establishment of the NAC would either reduce or abolish the contrast effect. However, contrary to this prediction, the results of the present study show that the NAC is insensitive to devaluation of the second, preferred, substance. This allows one to question that interpretation. The results reported in this study support the view that the NAC effect is controlled by memory of the relative value of the first solution, which is updated daily by means of both a gustatory and/or post-ingestive comparison of the first and second solutions, and memory of past pairings. (C) 2010 Elsevier B.V. All rights reserved.

Colony dehydration and water collection by specialized caste in the leaf-cutting ant Atta sexdens rubropilosa

Social organization enables leaf-cutting ants to keep appropriate micro-ecological nest conditions for the fungus garden (their main food), eggs, larvae and adults. To maintain stability while facing changing conditions, individual ants must perceive destabilising factors and produce a proper behavioral response. We investigated behavioral responses to experimental dehydration in leaf-cutting ants to verify if task specialization exists, and to quantify the ability of ant sub-colonies for water management. Our setup consisted of fourteen sub-colonies, ten of which were randomly assigned to different levels of experimental dehydration with silica gel, whereas the remaining four were controls. The ten experimental sub-colonies were split into two groups, so that five of them had access to water. Diverse ant morphs searched for water in dehydrated colonies, but mainly a caste of small ants collected water after sources had been discovered. Size specialization for water collection was replicable in shorter experiments with three additional colonies. Ants of dehydrated colonies accumulated leaf-fragments on the nest entrance, and covering the fungus garden. Behaviors that may enhance humidity within the nests were common to all dehydration treatments. Water availability increased the life span of dehydrated colonies.

Clock Genes, Melanopsins, Melatonin, and Dopamine Key Enzymes and Their Modulation by Light and Glutamate in Chicken Embryonic Retinal Cells

The avian circadian system is composed of the retina, the mammalian homolog region of the suprachiasmatic nucleus (SNC), and the pineal gland. The retina, itself, displays many rhythmic physiological events, such as movements of photoreceptor cells, opsin expression, retinal reisomerization, and melatonin and dopamine production and secretion. Altogether, these rhythmic events are coordinated to predict environmental changes in light conditions during the day, optimizing retina function. The authors investigated the expression pattern of the melanopsin genes Opn4x and Opn4m, the clock genes Clock and Per2, and the genes for the key enzymes N-Acetyltransferase and Tyrosine Hidroxylase in chicken embryo dispersed retinal cells. Primary cultures of chicken retina from 8-day-old embryos were kept in constant dark (DD), in 12-h light/12-h dark (12L:12D), in 12L:12D followed by DD, or in DD in the absence or presence of 100 mu M glutamate for 12 h. Total RNA was extracted throughout a 24-h span, every 3 h starting at zeitgeber time 0 (ZT0) of the 6th day, and submitted to reverse transcriptase-polymerase chain reaction (RT-PCR) followed by quantitative PCR (qPCR) for mRNA quantification. The data showed no rhythmic pattern of transcription for any gene in cells kept in DD. However under a light-dark cycle, Clock, Per2, Opn4m, N-Acetyltransferase, and Tyrosine Hydroxylase exhibited rhythmic patterns of transcription. In DD, 100 mu M glutamate was able to induce rhythmic expression of Clock, strongly inhibited the expression of Tyrosine Hydroxylase, and, only at some ZTs, of Opn4x and Opn4m. The neurotransmitter had no effect on Per2 and N-Acetyltransferase transcription. The authors confirmed the expression of the protein OPN4x by immunocytochemistry. These results suggest that chicken embryonic retinal cells contain a functional circadian clock, whose synchronization requires light-dark cycle or glutamate stimuli. (Author correspondence: amdlcast@ib.usp.br).

Purinergic signalling is involved in the malaria parasite Plasmodium falciparum invasion to red blood cells

Plasmodium falciparum, the most important etiological agent of human malaria, is endowed with a highly complex cell cycle that is essential for its successful replication within the host. A number of evidence suggest that changes in parasite Ca(2+) levels occur during the intracellular cycle of the parasites and play a role in modulating its functions within the RBC. However, the molecular identification of Plasmodium receptors linked with calcium signalling and the causal relationship between Ca(2+) increases and parasite functions are still largely mysterious. We here describe that increases in P. falciparum Ca(2+) levels, induced by extracellular ATP, modulate parasite invasion. In particular, we show that addition of ATP leads to an increase of cytosolic Ca(2+) in trophozoites and segmented schizonts. Addition of the compounds KN62 and Ip5I on parasites blocked the ATP-induced rise in [Ca(2+)](c). Besides, the compounds or hydrolysis of ATP with apyrase added in culture drastically reduce RBC infection by parasites, suggesting strongly a role of extracellular ATP during RBC invasion. The use of purinoceptor antagonists Ip5I and KN62 in this study suggests the presence of putative purinoceptor in P. falciparum. In conclusion, we have demonstrated that increases in [Ca(2+)](c) in the malarial parasite P. falciparum by ATP leads to the modulation of its invasion of red blood cells.

Role of alpha 7 Nicotinic Acetylcholine Receptor in Calcium Signaling Induced by Prion Protein Interaction with Stress-inducible Protein 1

The prion protein (PrP(C)) is a conserved glycosylphosphatidyl-inositol-anchored cell surface protein expressed by neurons and other cells. Stress-inducible protein 1 (STI1) binds PrP(C) extracellularly, and this activated signaling complex promotes neuronal differentiation and neuroprotection via the extracellular signal-regulated kinase 1 and 2 (ERK1/2) and cAMP-dependent protein kinase 1 (PKA) pathways. However, the mechanism by which the PrPC-STI1 interaction transduces extracellular signals to the intracellular environment is unknown. We found that in hippocampal neurons, STI1-PrP(C) engagement induces an increase in intracellular Ca(2+) levels. This effect was not detected in PrP(C)-null neurons or wild-type neurons treated with an STI1 mutant unable to bind PrP(C). Using a best candidate approach to test for potential channels involved in Ca(2+) influx evoked by STI1-PrP(C), we found that alpha-bungarotoxin, a specific inhibitor for alpha 7 nicotinic acetylcholine receptor (alpha 7nAChR), was able to block PrP(C)-STI1-mediated signaling, neuroprotection, and neuritogenesis. Importantly, when alpha 7nAChR was transfected into HEK 293 cells, it formed a functional complex with PrP(C) and allowed reconstitution of signaling by PrP(C)-STI1 interaction. These results indicate that STI1 can interact with the PrP(C).alpha 7nAChR complex to promote signaling and provide a novel potential target for modulation of the effects of prion protein in neurodegenerative diseases.

Adenosine receptor type 2a is differently modulated by nicotine in dorsal brainstem cells of Wistar Kyoto and spontaneously hypertensive rats

Hypertension can result from neuronal network imbalance in areas of central nervous system that control blood pressure, such as the nucleus tractus solitarius (NTS). There are several neurotransmitters and neuromodulatory substances within the NTS, such as adenosine, which acts on purinoreceptors A(2a) (A(2a)R). The A(2a)R modulates neurotransmission in the NTS where its activation may induce decrease in blood pressure by different mechanisms. Nicotine is a molecule that crosses the hematoencephalic barrier and acts in several areas of central nervous system including the NTS, where it may interact with some neurotransmitter systems and contributes to the development of hypertension in subjects with genetic predisposition to this disease. In this study we first determined A(2a)R binding, protein, and mRNA expression in dorsomedial medulla oblongata of neonate normotensive (WKY) and spontaneously hypertensive rats (SHR). Subsequently, we analyzed the modulatory effects of nicotine on A(2a)R in cell culture in order to evaluate its possible involvement in the development of hypertension. Data showed a decreased A(2a)R binding and increased protein and mRNA expression in tissue sample and culture of dorsal brainstem from SHR compared with those from WKY rats at basal conditions. Moreover, nicotine modulated A(2a)R binding, protein, and mRNA expression in cells from both strains. Interestingly, nicotine decreased A(2a)R binding and increased protein levels, as well as, induced a differential modulation in A(2a)R mRNA expression. Results give us a clue about the mechanisms involved in the modulatory effects of nicotine on A(2a)R as well as hypothesize its possible contribution to the development of hypertension. In conclusion, we demonstrated that A(2a)R of SHR cells which differ from WKY and nicotine differentially modulates A(2a)R in dorsal brainstem cells of SHR and WKY.

Activation of Leishmania (Leishmania) amazonensis arginase at low temperature by binuclear Mn(2+) center formation of the immobilized enzyme on a Ni(2+) resin

In Leishmania, arginase is responsible for the production of ornithine, a precursor of polyamines required for proliferation of the parasite. In this work, the activation kinetics of immobilized arginase enzyme from L. (L.) amazonensis were studied by varying the concentration of Mn(2+) applied to the nickel column at 23 degrees C. The intensity of the binding of the enzyme to the Ni(2+) resin was directly proportional to the concentration of Mn(2+). Conformational changes of the enzyme may occur when the enzyme interacts with immobilized Ni(2+), allowing the following to occur: (1) entrance of Mn(2+) and formation of the metal bridge; (2) stabilization and activation of the enzyme at 23 degrees C; and (3) an increase in the affinity of the enzyme to Ni(2+) after the Mn(2+) activation step. The conformational alterations can be summarized as follows: the interaction with the Ni(2+) simulates thermal heating in the artificial activation by opening a channel for Mn(2+) to enter. (C) 2010 Elsevier Inc. All rights reserved.