Biochemical and physiological characterization of a new Na+-channel specific peptide from the venom of the Argentinean scorpion Tityus trivittatus

A new peptide with 61 amino acids cross-linked by 4 disulfide bridges, with molecular weight of 6938.12 Da, and an amidated C-terminal amino acid residue was purified and characterized. The primary structure was obtained by direct Edman degradation and sequencing its gene. The peptide is lethal to mammals and was shown to be similar (95% identity) to toxin Ts1 (gamma toxin) from the Brazilian scorpion Tityus serrulatus; it was named Tt1g (from T. trivittatus toxin 1 gamma-like). Tt1g was assayed on several sub-types of Na⁺-channels showing displacement of the currents to more negative voltages, being the hNav1.3 the most affected channel. This toxin displays characteristics typical to the β-type sodium scorpion toxins. Lethality tests and physiological assays indicate that this peptide is probably the most important toxic component of this species of scorpion, known for causing human fatalities in the South American continent.     

Catastrophic disturbance, logging and the ecology of mahogany (Swietenia macrophylla King): grounds for listing a major tropical timber species in CITES

Recent debate on whether or not mahogany ( Swietenia macrophylla King) is threatened by the international timber trade has focused on the breadth of its range and estimates of the remaining stock of mahogany trees. These data are inadequate to reveal the status of mahogany populations, both because they are incomplete in areal extent and because they do not reveal population parameters such as the existence or density of young trees smaller than commercial size. However, there is sufficient information on the regeneration ecology of mahogany to indicate that under natural conditions this species regenerates in essentially even-aged stands after catastrophic disturbances destroy many or most trees, and, in the case of fires and flooding, saplings and seedlings as well. Adult mahoganies tend to survive these events, and regenerate by shedding seed onto the resulting gaps or clearings. This ecological strategy makes mahogany vulnerable to logging, first because juvenile mahoganies are not found in the understorey, and secondly because logging operations shortcircuit mahogany regeneration processes by selectively removing almost all mahogany seed sources while leaving standing competing vegetation of other species. Listing of mahogany in CITES Appendix II could provide both a mechanism to fill in gaps in information and an incentive to change current practices in favour of silvicultural management to provide for regeneration of this valuable timber species in forests subjected to logging.     

Temporal fluctuations and experimental effects in desert plant communities

In the Chihuahuan Desert of the southwestern United States we monitored responses of both winter and summer annual plant communities to natural environmental variation and to experimental removal of seed-eating rodents and ants for 13 years. Analyses of data on population densities of the species by principal component analysis (PCA) followed by repeated measures analysis of variance (rmANOVA) on PCA scores showed that: (1) composition of both winter and summer annual communities varied substantially from year to year, presumably in response to interannual climatic variation, and (2) community composition of winter annuals was also significantly affected by the experimental manipulations of seed-eating animals, but the composition of the summer annual community showed no significant response to these experimental treatments. Canonical discriminant analysis (CDA) was then applied to the data for winter annuals to more clearly identify the responses to the different classes of experimental manipulations. This analysis showed that removing rodents or ants or both taxa caused distinctive changes in species composition. There was a tendency for large-seeded species to increase on rodent removal plots and to decrease on ant removal plots, and for small-seeded species to change in the opposite direction. In the winter annual community there was a significant time x treatment interaction: certain combinations of species that responded differently to removal of granivores also showed opposite fluctuations in response to long-term climatic variation. The large year-to-year variation in the summer annual community was closely and positively correlated across all experimental treatments. The use of multivariate analysis in conjunction with long-term monitoring and experimental manipulation shows how biotic interactions interact with variation in abiotic conditions to affect community dynamics.     

A short-range endemic species from south-eastern Atlantic Rain Forest shows deep signature of historical events: phylogeography of harvestmen Acutisoma longipes (Arachnida: Opiliones)

The Brazilian Atlantic Rain Forest is amongst the most diverse biomes in the world, but the processes that shaped its biodiversity are still poorly understood. We used one mitochondrial and two nuclear markers to evaluate the phylogeographic patterns of the endemic harvestman Acutisoma longipes and its closely related species to investigate the biogeographic history of this biome. The results showed low intrapopulation diversity and strong population structure, suggesting poor dispersion amongst locations. Phylogenetic analyses pointed to three main mitochondrial lineages congruent with the geomorphology of the south-eastern region of Brazil (Serra do Mar, Serra da Mantiqueira, and interior plateau). These older divergences occurred in the middle-Neogene, suggesting that events in this period drove the diversification of the species, but Quaternary events also affected the populations locally. We detected some congruence between A. longipes demographic patterns and the areas of endemism delimited for harvestmen, suggesting that some regions of the distribution could have been more stable in the past (especially in Serra da Mantiqueira). Our findings corroborate that harvestmen are a suitable group for the study of ancient biogeographic events in the Atlantic Rain Forest, even at small-scale ranges. Acutisoma hamatum is here considered as a new junior synonym of A. longipes.     

Individualistic responses of forest herb traits to environmental change

• Intraspecific trait variation (ITV; i.e. variability in mean and/or distribution of plant attribute values within species) can occur in response to multiple drivers. Environmental change and land‐use legacies could directly alter trait values within species but could also affect them indirectly through changes in vegetation cover. Increasing variability in environmental conditions could lead to more ITV, but responses might differ among species. Disentangling these drivers on ITV is necessary to accurately predict plant community responses to global change.
• We planted herb communities into forest soils with and without a recent history of agriculture. Soils were collected across temperate European regions, while the 15 selected herb species had different colonizing abilities and affinities to forest habitat. These mesocosms (384) were exposed to two‐level full‐factorial treatments of warming, nitrogen addition and illumination. We measured plant height and specific leaf area (SLA).
• For the majority of species, mean plant height increased as vegetation cover increased in response to light addition, warming and agricultural legacy. The coefficient of variation (CV) for height was larger in fast‐colonizing species. Mean SLA for vernal species increased with warming, while light addition generally decreased mean SLA for shade‐tolerant species. Interactions between treatments were not important predictors.
• Environmental change treatments influenced ITV, either via increasing vegetation cover or by affecting trait values directly. Species’ ITV was individualistic, i.e. species responded to different single resource and condition manipulations that benefited their growth in the short term. These individual responses could be important for altered community organization after a prolonged period.

     

华北地区针叶林下凋落物层化学性质的研究

森林凋落物中贮积了大量的有机、无机养分物质,它是森林土壤自然肥力的重要来源之一。在森林生态系统中,养分物质的内部循环主要是通过凋落物来实现的。在分解、转化过