Respiratory gill surface of the serrasalmid fish, Piaractus mesopotamicus

Gill element dimensions of pacu Piaractus mesopotamicus were estimated and correlated to body mass ( W ), according to the power equation Y=aW^b . The filament number ( b =0.154) and length ( b =0.457) increased with body mass, markedly influencing the respiratory gill surface area ( b =0.769). The high filament number and length, associated with a high secondary lamellae frequency ( a =40.21), are typical of active fish species and may be an adaptation to its migratory movements during reproduction. The comparatively small dimensions of its secondary lamellae are found more commonly in less active species, and may be related to the environmental conditions prevailing in lentic environments, where the species is normally found most of the year. Such features, together with its ability to compensate for oxygen reduction by means of a high ventilatory volume, and the use of aquatic surface respiration (ASR), may account for its adaptative capacity to withstand hypoxic conditions, with a low respiratory energy cost.     

β-Amino acid residues: Conformational characterization of an N- and C-protected homo-β-(S)-leucine

Summary An N- and C-protected derivative ofhomo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates and extended conformation for thishomo-β-residue, with the ϕ torsion angle being more constrained than the μ and ψ angles.     

THE ASSOCIATION BETWEEN FLUCTUATING ASYMMETRY,TRAIT VARIABILITY,TRAIT HERITABILITY,AND STRESS: A MULTIPLY REPLICATED EXPERIMENT ON COMBINED STRESSES IN DROSOPHILA MELANOGASTER

A number of hypotheses have been proposed about the association between developmental stability phenotypic variability, heritability, and environmental stress. Stress is often considered to increase both the asymmetry and phenotypic variability of bilateral traits, although this may depend on trait heritability. Empirical studies of such associations often yield inconsistent results. This may reflect the diversity of traits and conditions used or a low repeatability of any associations. To test for repeatable associations between these variables, multiply replicated experiments were undertaken on Drosophila melanogaster using a combination stress at the egg, larval and adult stages of reduced protein, ethanol in the medium, and a cold shock. Both metric and meristic traits were measured and levels of heritable variation for each trait estimated by maximum likelihood and parent-offspring regression over three generations. Trait means were reduced by stress, whereas among-individual variation increased Fluctuating asymmetry (FA) was increased by stress in some cases, but few comparisons were significant. Only one trait orbital bristle, showed consistent increases in FA. Changes in trait means, trait phenotypic variability, and developmental stability as a result of stress were not correlated. Extreme phenotypes tended to have higher levels of FA but only the results for orbital bristles were significant. All traits had low to intermediate heritabilities except orbital bristle, which showed no heritable variation. Only traits with low heritability and high levels of phenotypic variability may show consistent increases in FA under stress. Overall, the independence of phenotypic variability, plasticity, and the developmental stability of traits extend to changes in these measures under stressful conditions.     

Nutrient Limitation to Primary Productivity in a Secondary Savanna in Venezuela1

We examined nutrient limitation to primary productivity in a secondary savanna in the interior branch of the Coastal Range of Venezuela, which was converted from forest to savanna more than 100 years ago. We manipulated soil nutrients by adding nitrogen (+N), phosphorus and potassium (+PK), and nitrogen, phosphorus, and potassium (+NPK) to intact savanna. Eleven months after fertilization, we measured aboveground biomass and belowground biomass as live fine roots in the top 20 cm of soil, and species and functional group composition in response to nutrient additions. Aboveground biomass was highest in the NPK treatment ([mean g/m2]; control = 402, +N = 718, +PK = 490, +NPK = 949). Aboveground production, however, appeared to be limited primarily by N. Aboveground biomass increased 78 percent when N was added alone but did not significantly respond to PK additions when compared to controls. In contrast to aboveground biomass, belowground biomass increased with PK additions but showed no significant increase with N (depth 0–20 cm; [mean g/m2]; control = 685, +N = 443, +PK = 827, +NPK = 832). There was also a 36 percent increase in root length with PK additions when compared to controls. Whole savanna shoot:root ratios were similar for control and +PK (0.6), while those for +N or +NPK fertilization were significantly higher (1.7 and 1.2, respectively). Total biomass response (above + belowground) to nutrient additions showed a strong N and PK co‐limitation ([mean g/m2]; control = 1073, +N = 1111, +PK = 1258, +NPK = 1713). Aboveground biomass of all monocots increased with N additions, whereas dicots showed no response to nutrient additions. Trachypogon spp. (T. plumosus+T. vestitus) and Axonopus canescens, the two dominant grasses, made up more than 89 percent of the total aboveground biomass in these sites. Trachypogon spp. responded to NPK, whereas A. canescens, sedges, and the remaining monocots only responded to N. Even though nutrient additions resulted in higher aboveground biomass in N and NPK fertilized plots, this had little effect on plant community composition. With the exception of sedges, which responded positively to N additions and increased from 4 to 8 percent of die plant community, no changes were observed in plant community composition after 11 months.     

Processes Driving Ontogenetic Succession of Galls in a Canopy Tree1

Herbivores can be associated with distinct ontogenetic stages of their host in a nonseasonal, directional, and continuous pattern of colonization and extinction of species populations called ontogenetic succession, but the processes behind this pattern are still largely unknown. We used plants of Cryptocarya aschersoniana Mez (Lauraceae) belonging to different ontogenetic stages, to examine how the density of different gall‐inducing insects varies along the ontogeny of the host, and how gall density is influenced by mechanisms associated with host quality (plant height, plant shape, leaf area, specific leaf area, and hypersensitivity), and by mechanisms associated with their natural enemies (parasitoids, pathogens, and predators). In a remnant of Araucaria Forest, located in the São Francisco de Paula National Forest (Brazil), gall density (ind./100 g of leaf ) was obtained for 42 plants of C. aschersoniana divided into three height classes. Two galling species were recorded, showing quite distinct density patterns among height classes of C. aschersoniana. While Hymenoptera gall density decreased almost 50 times from small plants to canopy trees, Hemiptera gall density increased almost 10 times. Path analyses showed that Hymenoptera density was higher in smaller plants, independent of other host traits, while Hemiptera density was higher in plants exhibiting smaller leaves. Natural enemies were not detected in the Hemiptera population, and mortality rates due to predators, parasitoids, and pathogens did not affect Hymenoptera density. Processes associated with plant quality play the main role in generating the observed ontogenetic succession pattern.     

Small mammal populations of an agroecosystem in the Atlantic Forest domain, southeastern Brazil.

This study reports 2 years of the population dynamics and reproduction of a small mammal community using the removal method. The study was conducted in a rural area of the Atlantic Forest, in Sumidouro, Rio de Janeiro State, Brazil. The population sizes, age structure and reproduction were studied for the four most common species in the study area. The overall diversity was 1.67 and ranged between 0.8 to 1.67. The species richness was 13 considering the whole study. The most abundant species were the rodents Nectomys squamipes (n = 133), Akodon cursor (n = 74), Oligoryzomys nigripes (n = 25) and the marsupials Didelphis aurita (n = 58) and Philander frenatus (n = 50). Seven other rodents were captured once: Necromys lasiurus, Akodon montensis, Sooretamys angouya, Oecomys catherine, Oxymycterus judex, Euryzygomatomys spinosus and Trinomys iheringi. There were higher peaks for diversity and species richness during the winter (dry) months, probably due to higher food availability. The marsupials had a seasonal reproduction with highest population sizes at the end of the rainy seasons. Nectomys squamipes reproduced mostly during rainy periods. Akodon cursor reproduced predominantly in the winter with the highest population peaks occurring during this season. The analysis of the population dynamics of the rodent species indicated that no species behaved as an agricultural pest, probably due to the heterogeneous landscape of high rotativity of vegetable cultivation. Rodent populations were more susceptible to the removal procedure than marsupial ones.     

Cytoskeletal rearrangement and cell death induced by Bothrops alternatus snake venom in cultured Madin-Darby canine kidney cells.

Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement and cytotoxicity caused by Bothrops alternatus venom in cultured Madin-Darby canine kidney (MDCK) cells. Incubation with venom (10 and 100 microg/mL) significantly (p <0.05) decreased the cellular uptake of neutral red dye after 1 and 3 h. Venom (100 microg/mL) also markedly decreased the transepithelial electrical resistance (RT) across MDCK monolayers. Staining with rhodamine-conjugated phalloidin revealed disarray of the cytoskeleton that involved the stress fibers at the basal cell surface and focal adhesion-associated F-actin in the cell-matrix contact region. Feulgen staining showed a significant decrease in the number of cells undergoing mitosis and an increase in the frequency of altered nuclei. Scanning electron microscopy revealed a decrease in the number of microvilli and the presence of cells with a fusiform format. Flow cytometry with annexin V and propidium iodide showed that cell death occurred by necrosis, with little apoptosis, a conclusion supported by the lack of DNA fragmentation characteristic of apoptosis. Pretreating the cells with catalase significantly attenuated the venom-induced loss of viability, indicating a possible involvement of H2O2 in the cellular damage; less protection was observed with superoxide dismutase or N omega-nitro-L-arginine methyl ester. These results indicate that Bothrops alternatus venom is cytotoxic to cultured MDCK cells, possibly via the action of reactive oxygen species. This cytotoxicity could contribute to nephrotoxicity after envenoming by this species.     

Guanine Nucleotides Inhibit cAMP Accumulation Induced by Metabotropic Glutamate Receptor Activation

Metabotropic glutamate receptors (mGluRs) have been shown to modulate adenylate cyclase activity via G-proteins. In the present study we report similar results to the previously observed in the literature, showing that glutamate and the metabotropic agonists, 1S,3R-ACPD or quisqualate induced cAMP accumulation in hippocampal slices of young rats. Moreover, guanine nucleotides GTP, GDP or GMP, inhibited the glutamate-induced cAMP accumulation. By measuring LDH activity in the buffer surrounding the slices, we showed that the integrity of the slices was maintained, indicating that the effect of guanine nucleotides was extracellular. GMP, GDP-S or Gpp(NH)p abolished quisqualate-induced cAMP accumulation. GDP-S or Gpp(NH)p but not GMP inhibited 1S,3R-ACPD-induced cAMP accumulation. The response evoked by glutamate was also abolished by the mGluR antagonists: L-AP3 abolished glutamate-induced cAMP accumulation in a dose-dependent manner and MCPG was effective only at the 2 mM dose. DNQX was ineffective. We are reporting here, an inhibition induced by guanine nucleotides, via an extracellular site (s), similar to the observed with classical glutamate antagonists on a cellular response evoked by mGluR agonists.