NEW METHODS FOR THE STUDY OF VERTICAL STRATIFICATION OF NEOTROPICAL OPOSSUMS.

Novos métodos vêm sendo desenvolvidos para o estudo da estratificação vertical dos pequenos mamíferos neotropicais, como alternativas aos métodos convencionais que usam armadilhas de captura de animais vivos. Nesta revisão descrevemos três métodos alternativos para estudar a estratificação vertical dos marsupiais didelfídeos nas florestas tropicais: testes de desempenho em uma abordagem ecomorfológica, carretel de rastreamento e ninhos artificiais. O histórico de uso de cada um é revisto, discutindo suas vantagens e desvantagens, e apresentando exemplos de resultados inéditos obtidos através de seu uso. Testes de hipóteses mais acurados sobre estruturação de comunidades locais e questões relacionadas à demografia de populações podem ser obtidos com a combinação destes novos métodos com métodos convencionais, que se complementem, minimizando suas deficiências.New methods have been developed for the study of vertical stratification on small neotropical mammals, alternative to traditional methods using live traps. We reviewed three such alternative methods to study vertical stratification of didelphid marsupials in tropical forests: performance tests in an ecomorphological approach, spool-and-line, and artificial nests. The history of each method was reviewed, discussing their advantages and pitfalls, and presenting examples of the unique results reac,hed. More accurate tests of hypothesis about assemblage structure and population demography can be obtained by combination of traditional and alternative methods, which complement each other, minimizing their limitations

Reações de Ortometalacão em Piridinas

In this paper we describe a powerful methodology for the regiospecific construction of polysubstituted aromatic and heteroaromatic compounds. The DoM reaction (direct ortho-metalation) comprises the deprotonation in position ortho of a aromatic or heteroaromatic containing DMG (directed metalation group) by strong bases, normally an alkyllithium reagent, leading to an ortho-lithiated species. These species, upon treatment with electrophilic reagents, gives 1,2 disubstituted products.

Disentangling the effects of habitat fragmentation and top-down trophic cascades on small mammal assemblages on Amazonian forest islands

Habitat loss and fragmentation are widely acknowledged to affect species diversity. However, the pathways through which their effects are propagated through foodwebs, ultimately driving species diversity, are less well understood. We investigated to what extent the effects of habitat loss and fragmentation on small mammals in Central Amazonia are mediated by higher trophic levels, specifically mammal mesopredators and apex predators. We surveyed these three mammal groups across 25 islands surrounded by a landscape-scale gradient of forest cover within the Balbina Hydroelectric Reservoir, in addition to three adjacent continuous forest sites. We then applied Structural Equation Modelling based on apex-predator incidence and either the abundance or biomass of mesopredators and small mammals. Apex-predator incidence was positively affected by landscape forest cover, as well as mesopredators abundance and biomass. Small mammal abundance, but not biomass, was negatively affected by forest cover. Contrary to expectations, the negative effect of forest cover on small mammal abundance was not mediated by a decrease in mesopredator abundance nor incidence of apex-predators. Instead, small mammal increase is apparently favoured by the proliferation of the few persisting smaller-bodied species which can take advantage of augmented resources related to habitat degradation. The further increment in small mammal abundance in the absence or lower abundance of predators might be prevented by the resource availability characterising these evergreen forests. Mammal assemblages seem to be primarily regulated by bottom-up forces. While this suggests a delayed extinction debt in Amazonian forest islands, remaining biodiversity might be poorly resilient to additional habitat disturbances

Species-area relationships induced by forest habitat fragmentation apply even to rarely detected organisms

Neotropical snakes have extremely low detection rates, hampering our understanding of their responses to habitat loss and fragmentation. We addressed this gap using a limited sample (50 individuals, 16 species) across 25 variable-size insular forest fragments within a hydroelectric lake and four adjacent mainland continuous forest sites, in Central Brazilian Amazonia. The number of species recorded on forest islands (1.55 ± 0.78) was much lower than that at continuous forest sites (5.0 ± 3.1), with no snakes being recorded at twelve islands smaller than 30 ha. As such, snake assemblages were positively affected by forest area, explaining 48% of the number of species, and negatively affected by island isolation. The markedly higher number of species recorded across continuous forest sites likely results from the availability of riparian habitats, which have virtually disappeared from the archipelagic landscape given the widespread inundation of lowland areas. To prevent further severe biodiversity loss, including those of poorly known rare taxa, conservation policies should avert the additional construction of mega-dams that create myriad of small islands, in addition to extensive reservoir lakes from which all riparian habitats are eliminated

Interpreting T-Cell Cross-reactivity through Structure: Implications for TCR-Based Cancer Immunotherapy

Immunotherapy has become one of the most promising avenues for cancer treatment, making use of the patient\u27s own immune system to eliminate cancer cells. Clinical trials with T-cell-based immunotherapies have shown dramatic tumor regressions, being effective in multiple cancer types and for many different patients. Unfortunately, this progress was tempered by reports of serious (even fatal) side effects. Such therapies rely on the use of cytotoxic T-cell lymphocytes, an essential part of the adaptive immune system. Cytotoxic T-cells are regularly involved in surveillance and are capable of both eliminating diseased cells and generating protective immunological memory. The specificity of a given T-cell is determined through the structural interaction between the T-cell receptor (TCR) and a peptide-loaded major histocompatibility complex (MHC); i.e., an intracellular peptide-ligand displayed at the cell surface by an MHC molecule. However, a given TCR can recognize different peptide-MHC (pMHC) complexes, which can sometimes trigger an unwanted response that is referred to as T-cell cross-reactivity. This has become a major safety issue in TCR-based immunotherapies, following reports of melanoma-specific T-cells causing cytotoxic damage to healthy tissues (e.g., heart and nervous system). T-cell cross-reactivity has been extensively studied in the context of viral immunology and tissue transplantation. Growing evidence suggests that it is largely driven by structural similarities of seemingly unrelated pMHC complexes. Here, we review recent reports about the existence of pMHC hot-spots for cross-reactivity and propose the existence of a TCR interaction profile (i.e., a refinement of a more general TCR footprint in which some amino acid residues are more important than others in triggering T-cell cross-reactivity). We also make use of available structural data and pMHC models to interpret previously reported cross-reactivity patterns among virus-derived peptides. Our study provides further evidence that structural analyses of pMHC complexes can be used to assess the intrinsic likelihood of cross-reactivity among peptide-targets. Furthermore, we hypothesize that some apparent inconsistencies in reported cross-reactivities, such as a preferential directionality, might also be driven by particular structural features of the targeted pMHC complex. Finally, we explain why TCR-based immunotherapy provides a special context in which meaningful T-cell cross-reactivity predictions can be made