What shapes the altitudinal range of a high mountain Mediterranean plant? Recruitment probabilities from ovule to seedling stage

Recruitment is a complex process consisting of sequential stages affected by biotic interactions and abiotic factors. Assessment of these sequential stages and corresponding subprocesses may be useful in identifying the most critical stages. Accordingly, to assess the factors that may determine the altitudinal range limits of the high mountain Mediterranean plant Silene ciliata, a set of demographic stages, from flower production to establishment of 2‐yr‐old plants, and their influence on recruitment probability were examined using a step‐by‐step approach. We integrated florivory, pollination and pre‐dispersal seed predation as pre‐dispersal factors, and seedling emergence and survival as post‐dispersal determinants of recruitment. Three populations were monitored at the southernmost margin of the species along its local altitudinal range. Previous studies suggest that seediness is strongly limited by summer drought especially at the lower boundary of the species, a situation that may worsen under current global warming. Our results showed that recruitment was mainly limited by low seed production in the pre‐dispersal stage and low seedling emergence and survival in the post‐dispersal stage, probably due to environmental harshness in summer. By contrast, biotic factors responsible for propagule loss, such as flower and fruit predation, had a minor effect on the probability of plant recruitment. Although the relative importance of transition probabilities was similar among populations along the altitudinal range, comparatively lower flower production significantly reduced the number of recruited plants at the lowest altitude population. This demographic bottleneck, together with increased competition with other species favoured by climate warming, might collapse population growth and limit persistence at the lower altitudinal range of the species, raising its low local altitudinal edge.     

Effects of selected pharmaceutical products on phagocytic activity in Elliptio complanata mussels

Municipal wastewaters are recognized as a major source of pharmaceutical and personal care products to the aquatic environment, thereby exposing biota to unknown chronic effects. This study sought to examine the immunotoxic effects of pharmaceutical and urban waste products on the freshwater mussel Elliptio complanata. Hemolymph samples were collected and treated in vitro with increasing concentrations of various drugs (bezafibrate, carbamazepine, fluoxetine, gemfibrozil, morphine, naproxen, novobiocin, oxytetracycline, sulfamethazole, sulfapyridine and trimethoprim) and urban waste related chemicals (coprostanol, caffeine, cotinine) for 24 h at 15 degrees C. In a parallel experiment, mussels were caged and placed in two final aeration lagoons for the treatment of domestic wastewaters. At the end of the exposure period, hemolymphs were tested for phagocytic activity, intracellular esterase activity, cell adherence and lipid peroxidation (LPO). The products that most increased phagocytosis were bezafibrate, gemfibrozil and trimethoprim, while novobiocin and morphine reduced its activity. Intracellular esterase activity was reduced most strongly with sulfamethazole, novobiocin, gemfibrozil, bezafibrate and carbamazepine. Cell adherence was decreased by oxytetracycline, novobiocin and naproxen, and increased by gemfibrozil, bezafibrate and sulfapyridine. Exposure to these products also modulated LPO in hemocytes. Coprostanol and naproxen were more potent to reduce LPO while novobiocin and sulfapyridine were the most potent to induce LPO. The potential to induce LPO was positively correlated with the number of functional groups on the molecule (i.e., its nucleophilicity). Mussels exposed to domestic wastewater treatment plant aeration lagoons had decreased intracellular esterase and phagocytic activity as well, suggesting immunosuppression. PPCPs (pharmaceuticals and personal care products) that are recognized to disrupt cytokine signalling network by the nitric oxide pathway and cell permeability were generally the most potent ones. The data suggest that PPCPs have the potential to cause adverse effects on the immune system of bivalves.     

Recombination in the ompA gene but not the omcB gene of Chlamydia contributes to serovar-specific differences in tissue tropism, immune surveillance, and persistence of the organism

Sequences of the major outer membrane protein (MOMP) gene (ompA) and the outer membrane complex B protein gene (omcB) from Chlamydia trachomatis, Chlamydia pneumoniae, and Chlamydia psittaci were analyzed for evidence of intragenic recombination and for linkage equilibrium. The Sawyer runs test, compatibility matrices, and index of association analyses provided substantial evidence that there has been a history of intragenic recombination at ompA including one instance of interspecies recombination between the C. trachomatis mouse pneumonitis strain and the C. pneumoniae horse N16 strain. Although none of these methods detected intragenic recombination within omcB, differences in divergence reported in earlier studies suggested that there has been intergenic recombination involving omcB, and the analyses presented in this study are consistent with this. For C. trachomatis, index-of-association analyses suggested a higher degree of recombination for C class than for B class strains and a higher degree of recombination in the downstream half of ompA. In concordance with these findings, many significant breakpoints were found in variable segments 3 and 4 of MOMP for the recombinant strains D/B120, G/UW-57, E/Bour, and LGV-98 identified in this study. We provide examples of how genetic diversity generated by repeated recombination in these regions may be associated with evasion of immune surveillance, serovar-specific differences in tissue tropism, and persistence.     

Neural activation and functional connectivity during motor imagery of bimanual everyday actions

Bimanual actions impose intermanual coordination demands not present during unimanual actions. We investigated the functional neuroanatomical correlates of these coordination demands in motor imagery (MI) of everyday actions using functional magnetic resonance imaging (fMRI). For this, 17 participants imagined unimanual actions with the left and right hand as well as bimanual actions while undergoing fMRI. A univariate fMRI analysis showed no reliable cortical activations specific to bimanual MI, indicating that intermanual coordination demands in MI are not associated with increased neural processing. A functional connectivity analysis based on psychophysiological interactions (PPI), however, revealed marked increases in connectivity between parietal and premotor areas within and between hemispheres. We conclude that in MI of everyday actions intermanual coordination demands are primarily met by changes in connectivity between areas and only moderately, if at all, by changes in the amount of neural activity. These results are the first characterization of the neuroanatomical correlates of bimanual coordination demands in MI. Our findings support the assumed equivalence of overt and imagined actions and highlight the differences between uni- and bimanual actions. The findings extent our understanding of the motor system and may aid the development of clinical neurorehabilitation approaches based on mental practice.     

Hydrology Affects Environmental and Spatial Structuring of Microalgal Metacommunities in Tropical Pacific Coast Wetlands

The alternating climate between wet and dry periods has important effects on the hydrology and therefore on niche-based processes of water bodies in tropical areas. Additionally, assemblages of microorganism can show spatial patterns, in the form of a distance decay relationship due to their size or life form. We aimed to test spatial and environmental effects, modulated by a seasonal flooding climatic pattern, on the distribution of microalgae in 30 wetlands of a tropical dry forest region: the Pacific coast of Costa Rica and Nicaragua. Three surveys were conducted corresponding to the beginning, the highest peak, and the end of the hydrological year during the wet season, and species abundance and composition of planktonic and benthic microalgae was determined. Variation partitioning analysis (as explained by spatial distance or environmental factors) was applied to each seasonal dataset by means of partial redundancy analysis. Our results show that microalgal assemblages were structured by spatial and environmental factors depending on the hydrological period of the year. At the onset of hydroperiod and during flooding, neutral effects dominated community dynamics, but niche-based local effects resulted in more structured algal communities at the final periods of desiccating water bodies. Results suggest that climate-mediated effects on hydrology can influence the relative role of spatial and environmental factors on metacommunities of microalgae. Such variability needs to be accounted in order to describe accurately community dynamics in tropical coastal wetlands.     

Ecophysiological factors affecting growth,sporulation and survival of the biocontrol agent Penicillium oxalicum

The effect of temperature, pH, water potential and sources of nitrogen and carbon on the biocontrol agent Penicillium oxalicum were studied in vitro. The fungus is xerotolerant, mesophillic and has a wide pH tolerance. The parameters evaluated (germination, germ tube length, growth rate and sporulation) showed different sensitivities to the environmental factors. Peptone and free amino acids gave the highest growth rates and high levels of sporulation. Xylose, mannose and fructose gave the highest growth rates and mannose induced strong sporulation. The effect of nutrients (mannose + arginine) and water potential was also studied in vivo. The xerotolerant character of the fungus was confirmed. From this study we consider Penicillium oxalicum ecologically competent to perform effectively as a biocontrol agent in the soil environment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evidence for a partial redundancy of the fibronectin-binding proteins for the transfer of mycoloyl residues onto the cell wall arabinogalactan termini of Mycobacterium tuberculosis

Mycobacterium tuberculosis produces a series of major secreted proteins, the fibronectin-binding proteins (Fbps), also known as the antigen 85 complex, that are believed to play an essential role in the pathogenesis of tuberculosis through their mycoloyltransferase activity required for maintaining the integrity of the bacterial cell envelope. Four different fbp genes are found in the genome of M. tuberculosis, but the reason for the existence of these Fbps sharing the same substrate specificity in vitro in mycobacteria is unknown. We have shown previously that, in the heterologous host, Corynebacterium glutamicum, FbpA, FbpB and FbpC can all add mycoloyl residues to the cell wall arabinogalactan and that, in M. tuberculosis, the cell wall mycoloylation decreases by 40% when fbpC is knocked out. To investigate whether the remaining 60% mycoloylation came from the activity of FbpA and/or FbpB, fbpA- and fbpB-inactivated mutant strains were biochemically characterized and compared with the previously studied fbpC-disrupted mutant. Unexpectedly, both mutants produced normally mycoloylated cell walls. Overproduction of FbpA, FbpB or FbpC, but not FbpD, in the fbpC-inactivated mutant strain of M. tuberculosis restored both the cell wall-linked mycolate defect and the outer cell envelope permeability barrier property. These results are consistent with all three enzymes being involved in cell wall mycoloylation and FbpC playing a more critical role than the others or, alternatively, FbpC is able to compensate for FbpA and FbpB in ways that these enzymes cannot compensate for FbpC, pointing to a partial redundancy of Fbps. In sharp contrast, FbpD does not appear to be an active mycoloyltransferase enzyme, as it cannot complement the fbpC-inactivated mutant. Most importantly, application of Smith degradation to the cell walls of transformants demonstrated that the multiple Fbp enzymes are redundant rather than specific for the various arabinogalactan mycoloylation regions. Neither FbpA nor FbpB attaches mycoloyl residues to specific sites but, like FbpC, each enzyme transfers mycoloyl residues onto the four sites present in the arabinogalactan non-reducing end hexaarabinosides.