Leaf damage and functional traits along a successional gradient in Brazilian tropical dry forests

Herbivory has significant impacts on individual plants and plant communities, both at ecological and evolutionary time scales. In this context, this study aims to evaluate herbivore damage and its relationship with leaf chemical and structural traits, nutritional status, and forest structural complexity along a successional gradient. We predicted that trees in early successional stages support conservative traits related to drought tolerance (high specific leaf mass and phenolics), whereas trees in light-limited, late successional stages tend to enhance light acquisition strategies (high nitrogen content). We sampled 261 trees from 26 species in 15 plots (50 × 20 m; five per successional stage). From each tree, twenty leaves were collected for leaf trait measures. Phenolic content increased whereas specific leaf mass and nitrogen content decreased from early to late stages. However, leaf damage did not differ among successional stages. Our results partially corroborate the hypothesis that early successional plants in tropical dry forests exhibit leaf traits involved in the conservative use of water. The unexpected decrease in nitrogen content along the chronosequence is likely related to the fact that thinner leaves with low specific leaf mass could have less nitrogen-containing mesophyll per unit area. Mechanisms affecting herbivory intensity varied across scales: at the species level, leaf damage was negatively correlated with tannin concentration and specific leaf mass; at the plot level, leaf damage was positively affected by forest structural complexity. Herbivory patterns in tropical forests are difficult to detect because abiotic factors and multiple top-down and bottom-up forces directly and indirectly affect herbivores.     

The change of behaviour of two strains of Leishmania after cultivation in a defined medium

Attempts have been made to characterize two strains of Leishmania that became infective to golden hamsters only after they had been maintained for several years in a chemically defined culture medium. Observations were made on the growth rates of promastigotes in vitro, course of infection in hamsters, morphology of amastigotes, and electrophoretic mobility patterns of eight isoenzymes. Information was obtained about the buoyant densities of n-DNA and k-DNA, and one strain was tested against monoclonal antibodies. The identity of both strains remains obscure.     

Molecular Identification of Candida Species in the Oral Microbiota of Individuals with Down Syndrome: A Case–Control Study

Mycopathologia - Candida species are common in the human oral microbiota and may cause oral candidiasis (OC) when the microbiota equilibrium is disturbed. Immunosuppressed individuals are...     

Stress distribution of three-unit fixed partial prostheses (conventional and pontic) supported by three or two implants: 3D finite element analysis of ductile materials

In implantology, when financial or biological feasibility limitations appear, it is necessary to use prostheses with geometries that deviate from the conventional, with a pontic in the absence of an intermediate implant. The aim of this study was analyze and understand the general differences in the stresses generated in implants, components and infrastructures according to the configuration of the prosthesis over three or two implants. Thus, this paper analyzes the von Mises equivalent stresses (VMES) of ductile materials on their external surfaces. The experimental groups: Regular Splinted Conventional Group (RCG), which had conventional infrastructures on 3 regular-length Morse taper implants (4x11?mm); Regular Splinted Pontic Group (RPG), which had infrastructures with intermediate pontics on 2 regular-length Morse taper implants (4x11?mm). The simulations of the groups were created with Ansys Workbench 10.0 software. The results revealed that the RPG presented greater areas of possible fragility due to higher stress concentrations, for example, in the cervical area of the union between the implant and component the top platform of the abutment, as well as greater coverage of the stress by the cervical implant threads. The RPG infrastructure was also more affected by stresses in the connection areas between the prostheses and on the occlusal surface. There is an advantage to using prostheses supported by a greater number of implants (RCG) because this decreases the stress in the analyzed structures and consequently improves stress dissipation to the supporting bone, which would preserve the system.     

Predicting arsenic bioavailability to hyperaccumulator Pteris vittata in arsenic-contaminated soils

Using chemical extraction to evaluate plant arsenic availability in contaminated soils is important to estimate the time frame for site cleanup during phytoremediation. It is also of great value to assess As mobility in soil and its risk in environmental contamination. In this study, four conventional chemical extraction methods (water, ammonium sulfate, ammonium phosphate, and Mehlich III) and a new root-exudate based method were used to evaluate As extractability and to correlate it with As accumulation in P. vittata growing in five As-contaminated soils under greenhouse condition. The relationship between different soil properties, and As extractability and plant As accumulation was also investigated. Arsenic extractability was 4.6%, 7.0%, 18%, 21%, and 46% for water, ammonium sulfate, organic acids, ammonium phosphate, and Mehlich III, respectively. Root exudate (organic acids) solution was suitable for assessing As bioavailability (81%) in the soils while Mehlich III (31%) overestimated the amount of As taken up by plants. Soil organic matter, P and Mg concentrations were positively correlated to plant As accumulation whereas Ca concentration was negatively correlated. Further investigation is needed on the effect of Ca and Mg on As uptake by P. vittata. Moreover, additional As contaminated soils with different properties should be tested.     

Do the phenology and functional stem attributes of woody species allow for the identification of functional groups in the semiarid region of Brazil?

The phenology of tree species in environments that are subject to strong climatic seasonality is mainly determined by water availability, which may vary as a function of wood density. The relationship among phenology, water potential, wood density and the capacity of water storage in the stem were determined for woody species of caatinga vegetation (dry forest) in the semiarid region of NE Brazil. Leaf flush and fall, flowering and fruiting events were recorded over a 31-month period, and the water potential was measured over a two-year period. These data were related to precipitation, water availability in the soil and photoperiod. Seven deciduous species exhibited low wood density (DLWD,?<0.5?g?cm^?3), high capacity of water storage in the stem (until 250?% of the dry weight) and high water potential during the year, as opposed to 15 deciduous species that showed high wood density (DHWD,?≥0.5?g?cm^?3). Leaf flush, flowering and the fruiting of DHWD species were related to precipitation, whereas these phenological events occurred at the end of the dry season and/or the beginning of the rainy season for DLWD species and were related to the photoperiod. The two evergreen species showed variations of water potential that were intermediate between those of DHWD and DLWD deciduous species, leaf flush during the dry season and flowering at the end of dry season. These results suggest the existence of three functional groups: evergreen species, DHWD deciduous species and DLWD deciduous species.     

Evolutionary history of the Pectoral Sparrow Arremon taciturnus: evidence for diversification during the Late Pleistocene

We focus on reconstructing a spatiotemporal scenario of diversification of a widespread South American species, the Pectoral Sparrow Arremon taciturnus (Aves: Passerellidae). This species is widely distributed in both the humid and the dry forests of South America and therefore provides an interesting model for understanding the connection between different biomes of South America. We examined nucleotide sequences of the mitochondrial genes Cytochrome b (cyt-b) and NADH subunit 2 (ND2) from 107 specimens, and one nuclear marker (intron 7 of the β-fibrinogen gene) from a subset of samples collected across the distribution ranges of A. t. taciturnus and A. t. nigrirostris. Six major lineages were recovered in the phylogenies that displayed high levels of variance of allele frequencies and corresponded to distinct geographical locations. The estimation of divergence times provided evidence that diversification of the six lineages of the Pectoral Sparrow occurred throughout the Late Pleistocene across major cis-Andean biomes and Amazonian interfluves. Our dataset for A. taciturnus provides further evidence that rivers in Amazonia constitute barriers promoting allopatric speciation, with occasional sharing of alleles among lineages, particularly those with adjacent distributions.     

Novel α‐ketoglutarate dioxygenase tfdA‐related genes are found in soil DNA after exposure to phenoxyalkanoic herbicides

Phenoxyalkanoic herbicides such as 2,4‐dichlorophenoxyacetate (2,4‐D), 2,4‐dichlorophenoxybutyrate (2,4‐DB) or mecoprop are widely used to control broad‐leaf weeds. Several bacteria have been reported to degrade these herbicides using the α‐ketoglutarate‐dependent, 2,4‐dichlorophenoxyacetate dioxygenase encoded by the tfdA gene, as the enzyme catalysing the first step in the catabolic pathway. The effects of exposure to different phenoxyalkanoic herbicides in the soil bacterial community and in the tfdA genes diversity were assessed using an agricultural soil exposed to these anthropogenic compounds. Total community bacterial DNA was analysed by terminal restriction fragment length polymorphism of the 16S rRNA and the tfdA gene markers, and detection and cloning of tfdA gene related sequences, using PCR primer pairs. After up to 4 months of herbicide exposure, significant changes in the bacterial community structure were detected in soil microcosms treated with mecoprop, 2,4‐DB and a mixture of both plus 2,4‐D. An impressive variety of novel tfdA gene related sequences were found in these soil microcosms, which cluster in new tfdA gene related sequence groups, unequally abundant depending on the specific herbicide used in soil treatment. Structural analysis of the putative protein products showed small but significant amino acid differences. These tfdA gene sequence variants are, probably, required for degradation of natural substrate(s) structurally related to these herbicides and their presence explains self‐remediation of soils exposed to phenoxyalkanoic herbicides.