Resource density regulates the foraging investment in higher termite species

1. Resource density can regulate the area that animals use. At low resource density, there is a conflict in terms of balance between costs of foraging and benefits acquired. The foraging of the higher termite Nasutitermes aff. coxipoensis consists of searching throughout trails and a building galleries phase. 2. In this study, a manipulative field experiment was used to test the hypothesis that colonies of N. aff. coxipoensis forage towards a more profitable balance between the establishment of trails and gallery construction at low resource density. 3. The experiment was conducted in north‐eastern Brazil. Seven experimental plots were established with a continuous increase in resource density (sugarcane baits). Entire colonies of N. aff. coxipoensis were transplanted from their original sites to the experimental plot, totalling 35 nests. The number, branches and total length of trails and galleries were quantified. 4. The results show that N. aff. coxipoensis optimises its foraging output, intensifying the establishment of trails at the cost of gallery construction when resource density is low. The number of trails, the number of trail branches and the total length of trails decreased with increasing resource density. Interestingly, at low resource density, the search effort was concentrated on forming longer and a greater number of trails, a small proportion of which were converted into galleries. The opposite relationship was observed at high resource density. 5. These results suggest an optimisation of search efforts during foraging depending on resource density, a mechanism that may help researchers to understand the use of space by higher termite species.     

Sulphadoxine-pyrimethamine alters the antioxidant defense system in blood of rabbit

Sulphadoxine-pyrimethamine (SP) despite reported resistance remains an important drug of choice for the treatment and control of malaria in most endemic areas. Exacerbation of intra-erythrocytic oxidative stress might contribute to the process of elimination of malaria parasites in the body. The effect of treatment with SP on the antioxidant defense system was investigated using rabbit as a model. Ten male rabbits were divided into two groups of five animals each. The first group was administered with normal saline and served as control. The second group received a single dose of SP (26.25mg/kg body weight). Blood samples were collected before and at 6, 12 and 24 h after drug administration. Activity of cellular enzymatic antioxidants, superoxide dismutase (SOD) and catalase (CAT), and level of reduced glutathione (GSH) were assayed using standard spectrophotometric methods. Serum lipid peroxidation was assessed by the formation of thiobarbituric acid reactive species (TBARS) while protein content was assayed by the method of Lowry et al., 1951. SOD activity was observed to increase progressively by 4.9, 63.4 and 120.8% at 6, 12 and 24 h respectively, after drug administration. Similarly, CAT activity increased by 44.5, 82.6 and 116.3% at 6, 12 and 24 h, respectively. TBARS level also increased significantly by 45.5, 118.2 and 186.4%, respectively. However, the level of GSH decreased by 41.9% at 6 h and remained so up till the 12 h, but by 24 h after drug administration, the level of the thiol substance has increased considerably up to 48.4% above the baseline level. SP treatment altered the antioxidant defense system in blood and may therefore induce oxidative stress by generating reactive oxygen species. This might play significant role in the therapeutic and adverse effects associated with the drug.     

Termite cohabitation: the relative effect of biotic and abiotic factors on mound biodiversity

1. Termites are important ecosystem engineers that improve primary productivity in trees and animal diversity outside their mounds. However, their ecological relationship with the species nesting inside their mounds is poorly understood. 2. The presence of termite cohabitant colonies inside 145 Cornitermes cumulans mounds of known size and location was recorded. Using network‐theoretical methods in conjunction with a suite of statistical analyses, the relative influence of biotic and abiotic drivers of termite within‐mound diversity on the composition and species richness of the termite community was investigated, specifically builder presence and physical aspects of the mound. 3. We found that richness inside the mound increases with mound size, and the species similarity between mounds decreases with distance. The physical attributes (abiotic drivers) of termite mounds (size and relative distance to other mounds) are the strongest predictors of termite species richness and composition. The biotic driver (presence of a builder colony) has an important, though smaller, negative effect on within‐mound termite species richness. 4. The findings suggest that the termites' physical manipulation of their environment is an important driver of within‐mound community diversity. More generally, the approach taken here, using a combination of statistical and network‐theoretical methods, can be used to determine the relative importance of abiotic and biotic drivers of diversity in a wide range of communities of interacting species.     

Strong seasonal disequilibrium measured between the oxygen isotope signals of leaf and soil CO2 exchange

The oxygen isotope composition (δ¹⁸O) of atmospheric CO₂ is among a very limited number of tools available to constrain estimates of the biospheric gross CO₂ fluxes, photosynthesis and respiration at large scales. However, the accuracy of the partitioning strongly depends on the extent of isotopic disequilibrium between the signals carried by these two gross fluxes. Chamber‐based field measurements of total CO₂ and CO¹⁸O fluxes from foliage and soil can help evaluate and refine our models of isotopic fractionation by plants and soils and validate the extent and pattern of isotopic disequilibrium within terrestrial ecosystems. Owing to sampling limitations in the past, such measurements have been very rare and covered only a few days. In this study, we coupled automated branch and soil chambers with tuneable diode laser absorption spectroscopy techniques to continuously capture the δ¹⁸O signals of foliage and soil CO₂ exchange in a Pinus pinaster Aït forest in France. Over the growing season, we observed a seasonally persistent isotopic disequilibrium between the δ¹⁸O signatures of net CO₂ fluxes from leaves and soils, except during rain events when the isotopic imbalance became temporarily weaker. Variations in the δ¹⁸O of CO₂ exchanged between leaves, soil and the atmosphere were well explained by theory describing changes in the oxygen isotope composition of ecosystem water pools in response to changes in leaf transpiration and soil evaporation.