Relative influence of deterministic processes on structuring marsh plant communities varies across an abiotic gradient

Understanding the processes determining community structure is one of the major goals of ecological research. Both deterministic and stochastic processes may shape community structure. The challenge is to understand the relative influence of each type of process across different environmental conditions. We investigated the influence of deterministic and stochastic processes on plant community assembly in tidal marshes across a strong abiotic (salinity) gradient in three estuaries in Georgia, USA using probabilistic Raup–Crick community dissimilarity. Our results indicated that deterministic processes had an increasingly important influence on structuring plant communities in salt and brackish marshes, probably due to high heterogeneity of microhabitats produced by the interplay between abiotic stress and biotic interactions. In contrast, the influence of deterministic processes on plant community assembly decreased in tidal freshwater marshes, suggesting an increasingly important role of stochastic processes in plant community assembly in tidal freshwater marshes, probably due to the higher species richness, higher recruitment from seed, and lower levels of abiotic stress in these habitats. At the estuarine scale (across tidal freshwater, brackish and salt marshes in each estuary), our results suggested that deterministic processes also had a relatively important influence on shaping plant community structure. Our results illustrated that plant community structure in tidal marshes is influenced by both deterministic and stochastic processes, but that the relative influence of these two types of processes varies across estuarine landscapes.     

Effect of fenitrothion on Spodoptera exigua larval development and ultrastructure of follicle cells

The effect of four sublethal concentrations (from 0.01165 to 0.3025 μg per insect, responding to LC₁₀/10, LC₁₀, LC₃₀ and LC₅₀) of the organophosphorus insecticide, fenitrothion, on Spodoptera exigua (Lepidoptera, Noctuidae) larval development and ultrastructure of follicular cells of adult female moths was tested. The most prominent malformations were: breaks in the cuticle, increased mortality during larval/pupal molting, alterations of nuclear envelope, changed heterochromatin pattern and abnormalities in mitochondrial ultrastructure. Some of the alterations are dose-dependent, but the other ones, like organization of rough endoplasmic reticulum (RER), show non-linear response: cells exposed to lower concentrations (LC₁₀/10 and LC₁₀) of the insecticide possessed clusters of accumulated RER, which were absent within the cells exposed to higher ones (LC₃₀ and LC₅₀). Formation of the eggshell was also markedly postponed within the groups exposed to lower doses. These findings prove that even minute amounts of xenobiotics may cause significant changes within exposed populations.     

TGF-beta1 gene polymorphisms influence the course of the disease in non-Hodgkin's lymphoma patients

Non-Hodgkin's lymphomas (NHL) constitute a heterogenous group of mainly B-cell lymphoproliferative diseases with different patterns of clinical behaviour. Biological mechanisms leading to development of NHL are not clearly understood. Transforming growth factor-beta1 (TGF-beta1) influences B cell growth and development. The present study aimed to determine whether there is an association between the polymorphic features located within the TGF-beta1 gene in NHL patients and progression of the disease. Two single nucleotide polymorphisms at positions 869 T/C (Leu10Pro) and 915 G/C (Arg25Pro) in the precursor region of the TGF-beta1 gene were determined in 55 NHL patients and 50 healthy individuals by PCR-SSP technique using commercial primers. In univariate analysis the presence of TGF-beta1 high producer genotypes (T/T G/G or T/C G/G) was found to significantly associate with an increased number of extranodal sites (11/30 vs 3/25, p=0.035 for two or more extranodal sites in patients having or lacking the TGF-beta1 high producer genotype, respectively). TGF-beta1 high producer genotype together with other clinical and biological factors (patient sex and age, stage and aggressiveness of the disease, presence of B symptoms, serum LDH level) were subjected to multivariate logistic regression analyses for the number of extranodal sites. Multivariate analysis confirmed the role of TGF-beta1 high producer genotype as a risk factor of NHL manifestation in two or more extranodal sites (OR=7.217, p=0.043) in addition to histological aggressiveness of the disease (OR=4.302, p=0.057). TGF-beta1 gene polymorphisms were found to associate with the course of the disease in NHL patients. TGF-beta1 high producer genotype appeared as an independent risk factor of extranodal manifestation of the disease.     

Independent colonization of multiple urban centres by a formerly forest specialist bird species

Urban areas are expanding rapidly, but a few native species have successfully colonized them. The processes underlying such colonization events are poorly understood. Using the blackbird Turdus merula, a former forest specialist that is now one of the most common urban birds in its range, we provide the first assessment of two contrasting urban colonization models. First, that urbanization occurred independently. Second, that following initial urbanization, urban-adapted individuals colonized other urban areas in a leapfrog manner. Previous analyses of spatial patterns in the timing of blackbird urbanization, and experimental introductions of urban and rural blackbirds to uncolonized cities, suggest that the leapfrog model is likely to apply. We found that, across the western Palaearctic, urban blackbird populations contain less genetic diversity than rural ones, urban populations are more strongly differentiated from each other than from rural populations and assignment tests support a rural source population for most urban individuals. In combination, these results provide much stronger support for the independent urbanization model than the leapfrog one. If the former model predominates, colonization of multiple urban centres will be particularly difficult when urbanization requires genetic adaptations, having implications for urban species diversity.     

Calorimetric studies of the effect of cis-carotenoids on the thermotropic phase behavior of phosphatidylcholine bilayers

Carotenoid geometry is a factor that determines their solubility and orientation in the lipid membrane as well as antioxidant capacities and bioavailability. The effects of the cis-isomers of carotenoids (zeaxanthin and β-carotene) on the thermotropic properties of lipid membranes formed with dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) were investigated by means of differential scanning calorimetry. The results were compared with the effects caused by the all-trans-isomer. Both the trans and cis isomers of zeaxanthin shifted the main phase transition temperature to lower values and decreased the cooperativity of the phase transition. The effect of all-trans zeaxanthin on the physical properties of the lipid bilayers has been shown to strongly depend on the hydrocarbon chain length of the membrane. In the case of cis-zeaxanthin this relationship is weaker.     

Atomic force microscopy studies of the adhesive properties of DPPC vesicles containing β-carotene

A role of carotenoids as modulators of physical properties of model and biological membranes has been already postulated. However, there is a lack of information on the influence of these pigments on interactions between the lipids which form such membranes. This paper applies atomic force microscopy (AFM) in to study the effects of β-carotene on the adhesion properties of DPPC multilamellar liposomes. This allowed us to gain, for the first time, a direct insight into the interactions between the components in model systems on a molecular level. We observe that the adhesive forces in DPPC multilamellar liposomes containing 1mol% of β-carotene decrease exponentially with increasing temperature, and that at about 37°C they diminish. In the case of pure liposomes the decline in adhesion is of a different nature and the adhesive forces disappear at 34°C. The adhesive forces are about 5 times higher at 31°C in the presence of β-carotene than in its absence. However, measurements using differential scanning calorimetry (DSC) showed a shift of the lamellar-to-undulled-lamellar phase transition toward lower temperatures by about 0.8 ± 0.2°C in a system containing β-carotene. The enthalpy changes (ΔH) of this transition are similar for both systems. For the main transition, gel-to-liquid crystalline, the peak is shifted by about 0.5 ± 0.1°C, and ΔH decreases by about 30% in liposomes treated with β-carotene in comparison to pure liposomes. Our results suggest increased cooperation between liposome components in a system with enriched β-carotene, which cause a change in phase transition temperatures. Moreover, these interactions are very sensitive to temperature.     

The changes in the antioxidant status of heart during experimental hypomagnesemia in balb/c mice

The present experiment was performed to assess if hypomagnesemia can influence antioxidant status in mice heart. The results could explain possibly a free radical theory of heart damage in magnesium deficiency. We used a rodent model of hypomagnesemia. The magnesium sufficient group received a standard diet whereas a magnesium deficient group received the diet containing a trace amount of magnesium. The activities of the most important antioxidant enzymes – catalase, glutathione peroxidase and superoxide dismutase were assessed in mice heart and liver in a time dependent manner, on the 10th and the 20th day of experiment. The level of magnesium in plasma of animals receiving the magnesium deficient diet dropped twice after the 8th day and four times after the 13th day and then reached a plateau value. The activity of catalase in heart in the magnesium deficient group increased gradually and was significantly (P<0.05) elevated by 27% on the 20th day of experiment whereas the superoxide dismutase activity was significantly decreased by 17% on the 20th day. Glutathione peroxidase activity was insignificantly elevated. The alterations of antioxidant enzyme activities in the heart indicate cardiomyocytes's exposure to oxidative stress, which can be responsible for the cardiac lesions observed during hypomagnesemia.     

Fatty acid composition of the parasitic mite Varroa destructor and its host the worker prepupae of Apis mellifera

The present study analyzes the fatty acid (FA) profile of lipids isolated from Varroa destructor Anderson & Trueman, a parasitic mite of the honey bee (Apis mellifera L.), uninfected and infected worker prepupae of the Carnolian subspecies Apis mellifera carnica Pollmann, and bee bread fed to the worker brood. Significant differences are observed in the FA profiles of lipids isolated from parasites, hosts and bee bread. Parasitism by V. destructor (henceforth, varroosis) induces visible changes in the lipid profile of worker prepupae. In infected prepupae, the percentage of total saturated FAs is lower and the percentage of unsaturated FAs is higher than in uninfected insects. These differences result from significant changes in the percentages of FAs that are most abundant in the evaluated groups (i.e. C16:0, C18:1 9c, C18:2n‐6 and C18:3n‐3 FAs). In mites and in uninfected and infected prepupae, the predominant FAs are oleic acid (41.07 ± 2.26%, 42.79 ± 1.21% and 45 ± 0.20%, respectively) and palmitic acid (22.62 ± 0.87%, 39.48 ± 0.43% and 36.84 ± 0.22%, respectively). Highly significant differences in FA composition are noted between bee bread and worker brood. The results suggest specific mechanisms of FA uptake, accumulation and metabolism in the food chain of this parasitic association, beginning from the food processed by nurse bees for larval feeding, through host organisms (worker brood) to V. destructor mites.