Fasciola hepatica: an antigen fraction derived from newly excysted juveniles, containing an immunoreactive 32-kDa protein, induces strong protective immunity in rats

Crude antigens of adult Fasciola hepatica and of newly excysted juveniles (NEJ) and a low-molecular-weight fraction of antigen from NEJs were tested for inducing protective immunity in rats. Two routes of vaccination were applied. The results showed that intraperitoneal vaccination induced significantly better protection (P <0.05) than intramuscular vaccination. Intraperitoneal vaccination with antigens from NEJs induced more effective protection: after challenge infection, rats that were so vaccinated had 92.6% (+/-2.5% SEM) fewer parasites in their liver and 57.3% (+/-13.3% SEM) fewer parasites penetrating the gut wall than control rats. Rats that were vaccinated with a low-molecular-weight fraction of antigen from NEJs were also highly protected against a challenge. F. hepatica antigens that are immunoreactive were identified on immunoblots, using sera collected from highly protected rats that had been vaccinated with NEJ antigens and also sera from cattle and rats that were experimentally infected with F. hepatica. The low-molecular-weight fraction of antigen from NEJs contained an immunodominant 32-kDa protein that was recognized by serum antibodies of vaccinated rats and immune cattle. This 32-kDa protein was not detected in partially purified antigens from adult flukes. We conclude that antigens of NEJs of F. hepatica, when injected intraperitoneally in rats, are highly protective. In particular, the 32-kDa protein contained in these antigens may be highly valuable for the development of an effective vaccine against F. hepatica.     

Improved tests for heterogeneity across a region of DNA sequence in the ratio of polymorphism to divergence

The neutral theory of molecular evolution predicts that the ratio of polymorphisms to fixed differences should be fairly uniform across a region of DNA sequence. Significant heterogeneity in this ratio can indicate the effects of balancing selection, selective sweeps, mildly deleterious mutations, or background selection. Comparing an observed heterogeneity statistic with simulations of the heterogeneity resulting from random phylogenetic and sampling variation provides a test of the statistical significance of the observed pattern. When simulated data sets containing heterogeneity in the polymorphism-to-divergence ratio are examined, different statistics are most powerful for detecting different patterns of heterogeneity. The number of runs is most powerful for detecting patterns containing several peaks of polymorphism; the Kolmogorov-Smirnov statistic is most powerful for detecting patterns in which one end of the gene has high polymorphism and the other end has low polymorphism; and a newly developed statistic, the mean sliding G statistic, is most powerful for detecting patterns containing one or two peaks of polymorphism with reduced polymorphism on either side. Nine out of 27 genes from the Drosophila melanogaster subgroup exhibit heterogeneity that is significant under at least one of these three tests, with five of the nine remaining significant after a correction for multiple comparisons, suggesting that detectable evidence for the effects of some kind of selection is fairly common.      

Isotopic analysis of cyanobacterial nitrogen fixation associated with subarctic lichen and bryophyte species

Dinitrogen fixation by cyanobacteria is of particular importance for the nutrient economy of cold biomes, constituting the main pathway for new N supplies to tundra ecosystems. It is prevalent in cyanobacterial colonies on bryophytes and in obligate associations within cyanolichens. Recent studies, applying interspecific variation in plant functional traits to upscale species effects on ecosystems, have all but neglected cryptogams and their association with cyanobacteria. Here we looked for species-specific patterns that determine cryptogam-mediated rates of N₂ fixation in the Subarctic. We hypothesised a contrast in N₂ fixation rates (1) between the structurally and physiologically different lichens and bryophytes, and (2) within bryophytes based on their respective plant functional types. Throughout the survey we supplied ¹⁵N-labelled N₂ gas to quantify fixation rates for monospecific moss, liverwort and lichen turfs. We sampled fifteen species in a design that captures spatial and temporal variations during the growing season in Abisko region, Sweden. We measured N₂ fixation potential of each turf in a common environment and in its field sampling site, in order to embrace both comparativeness and realism. Cyanolichens and bryophytes differed significantly in their cyanobacterial N₂ fixation capacity, which was not driven by microhabitat characteristics, but rather by morphology and physiology. Cyanolichens were much more prominent fixers than bryophytes per unit dry weight, but not per unit area due to their low specific thallus weight. Mosses did not exhibit consistent differences in N₂ fixation rates across species and functional types. Liverworts did not fix detectable amounts of N₂. Despite the very high rates of N₂ fixation associated with cyanolichens, large cover of mosses per unit area at the landscape scale compensates for their lower fixation rates, thereby probably making them the primary regional atmospheric nitrogen sink.     

Local and relational judgements of surface colour: constancy indices and discrimination performance

Colour constancy is generally assumed to arise from a combination of perceptual constancy mechanisms operating to partially discount illumination changes and relational mechanisms involved in judging the colour relationships between object surfaces. Here we examined the characteristics of these mechanisms using a 'yes/no' task. Subjects judged whether a target colour patch embedded in an array of coloured patches (a) stayed the same across a simulated temporal illuminant change (local colour judgement), or (b) changed in a manner consistent with the illuminant change (relational colour judgement). The colour of the target patch remained constant in one-third of the trials, changed in accord with the illuminant shift in another third, and shifted partially with the illuminant change in the remaining third. We found that perceptual constancy was relatively weak and relational constancy strong, as assessed using a modified colour constancy index. Randomising the spatial positions of coloured patches across the illuminant change did not affect subjects' constancy indices. Application of signal detection analysis revealed some otherwise hidden effects. In the case of relational judgements, subjects adopted more conservative criteria (fewer true and false positives) with randomisation, maintaining a constant level of discrimination performance (d'). For local judgements, randomisation led to small increases in performance but no changes in criteria. We conclude that signal detection theory provides a useful tool to supplement conventional approaches to understanding colour constancy.     

Gelatin-based microcarriers as embryonic stem cell delivery system in bone tissue engineering: an in-vitro study

Mouse embryonic stem cells were cultured on commercially available biodegradable macroporous microcarriers. A culture period of 1-2 weeks was needed to colonize the microcarriers. Embryonic stem cells retained their pluripotency for up to 14 days when cultured in medium supplemented with leukemia inhibitory factor. Replacing this medium by differentiation medium for 2 weeks initiated osteogenic differentiation. Encapsulation of the cell-loaded microcarriers in photopolymerizable polymers (methacrylate-endcapped poly-D,L-lactide-co-caprolactone), triacetin/hydroxyethylmethacrylate (HEMA) as solvent and with/without gelatin as porogen, resulted in a homogeneous distribution of the microcarriers in the polymer. As observed by transmission electron microscopy, viability of the cells was optimal when gelatin was omitted and when using triacetin instead of HEMA.     

Inclusion of ecologically based trait variation in plant functional types reduces the projected land carbon sink in an earth system model

Earth system models demonstrate large uncertainty in projected changes in terrestrial carbon budgets. The lack of inclusion of adaptive responses of vegetation communities to the environment has been suggested to hamper the ability of modeled vegetation to adequately respond to environmental change. In this study, variation in functional responses of vegetation has been added to an earth system model (ESM) based on ecological principles. The restriction of viable mean trait values of vegetation communities by the environment, called ‘habitat filtering’, is an important ecological assembly rule and allows for determination of global scale trait–environment relationships. These relationships were applied to model trait variation for different plant functional types (PFTs). For three leaf traits (specific leaf area, maximum carboxylation rate at 25 °C, and maximum electron transport rate at 25 °C), relationships with multiple environmental drivers, such as precipitation, temperature, radiation, and CO₂, were determined for the PFTs within the Max Planck Institute ESM. With these relationships, spatiotemporal variation in these formerly fixed traits in PFTs was modeled in global change projections (IPCC RCP8.5 scenario). Inclusion of this environment‐driven trait variation resulted in a strong reduction of the global carbon sink by at least 33% (2.1 Pg C yr^?1) from the 2nd quarter of the 21st century onward compared to the default model with fixed traits. In addition, the mid‐ and high latitudes became a stronger carbon sink and the tropics a stronger carbon source, caused by trait‐induced differences in productivity and relative respirational costs. These results point toward a reduction of the global carbon sink when including a more realistic representation of functional vegetation responses, implying more carbon will stay airborne, which could fuel further climate change.