Temporally Resolved Fluctuation Analysis of Sleep ECG

The correlation behavior in the heart beat rate significantly differs with respect to light sleep, deep sleep, and REM sleep. We investigate whether fluctuations of the heart beat rhythm may serve as a surrogate parameter for rapidly changing sleep phenomena, and if these changes are accessible by progressive beat-by-beat analysis of the sleep electrocardiogram (ECG).     

The effect of temperature on C(4)-type leaf photosynthesis parameters

C(4)-type photosynthesis is known to vary with growth and measurement temperatures. In an attempt to quantify its variability with measurement temperature, the photosynthetic parameters - the maximum catalytic rate of the enzyme ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) (V(cmax)), the maximum catalytic rate of the enzyme phosphoenolpyruvate carboxylase (PEPC) (V(pmax)) and the maximum electron transport rate (J(max)) - were examined. Maize plants were grown in climatic-controlled phytotrons, and the curves of net photosynthesis (A(n)) versus intercellular air space CO(2) concentrations (C(i)), and A(n) versus photosynthetic photon flux density (PPFD) were determined over a temperature range of 15-40 degrees C. Values of V(cmax), V(pmax) and J(max) were computed by inversion of the von Caemmerer & Furbank photosynthesis model. Values of V(pmax) and J(max) obtained at 25 degrees C conform to values found in the literature. Parameters for an Arrhenius equation that best fits the calculated values of V(cmax), V(pmax) and J(max) are then proposed. These parameters should be further tested with C(4) plants for validation. Other model key parameters such as the mesophyll cell conductance to CO(2) (g(i)), the bundle sheath cells conductance to CO(2) (g(bs)) and Michaelis-Menten constants for CO(2) and O(2) (K(c), K(p) and K(o)) also vary with temperature and should be better parameterized.     

On Haldane's formulation of Luria and Delbrück's mutation model

Two formulations of Luria and Delbrück's mutation model have been in common use since the 1940s. While mathematicians focused their attention on the formulation of Lea and Coulson that assumes asynchronous cell growth, biologists found more appealing the formulation of Haldane that assumes synchronous cell growth. This article attempts to solve several outstanding issues for the latter formulation. First, it provides an exact, closed-form expression for the mutant distribution by correcting a minor error in the literature. Second, it presents a novel algorithm for computing the mutant distribution, which leads to novel methods for computing point and interval estimates of mutation rates based on the maximum likelihood principle. Third, it critically examines existing methods based on the mean number of mutants. Finally, it compares the two formulations to underline their strengths and shortcomings.     

The influence of cyclic heating and cooling on <Emphasis Type="Italic">Escherichia coli</Emphasis> survival

Repeated heating and cooling in lethal (2–52°C) and nonlethal (2–37°C) temperature ranges resulted in cell death of Escherichia coli B/r and E. coli B_S?1 suspended in 0.01 M phosphate buffer, pH 7.0 at varying osmotic pressure, but not in cow’s milk. The lethal effect increased with the rate of heating and cooling and with increasing suspension media tonicity; it may be caused by the temperature destabilization of cellular osmotic homeostasis.     

Surface tension effects on instability in viscoelastic respiratory fluids

This paper establishes the mathematical formalism for the modeling of the mucus layer in the human trachea as a viscoelastic multiphase fluid system with surface tension with a view toward study of instability properties of the air-mucus system aimed at improving the design of new bioaerosol suppressing medication. The effects of surface tension, previously only conjectured and very poorly understood, are clearly established with quantitative relationships. Several very important physiological conclusions are obtained supporting one method of potential treatment and prevention of disease transmission by alteration of the mucus layer properties over other potential methods.     

Are correlations among foliar traits in ferns consistent with those in the seed plants?

Broad-based studies of gymnosperms and angiosperms reveal consistent and functionally significant correlations among foliar traits such as leaf mass per area (LMA), maximum photosynthetic rate (A(area)), foliar nitrogen (N(area)), foliar chlorophyll (Chl) and leaf longevity. To assess the generality of these relationships, we studied 20 fern species growing in the understorey of a temperate deciduous forest. We found that foliar N(area) increases with LMA, and that foliar N(area) and A(area) are positively correlated with one another, as are foliar N(area) and Chl. The ferns in general have very low LMA compared with most seed plants; A(area), N(area) and Chl are below median values for seed plants but are not extreme. Species with overwintering fronds have significantly higher LMA than species with fronds that senesce at the end of the growing season, as well as a significantly higher C : N ratio in frond tissue and relatively high foliar N on an areal basis. Correlations among foliar traits associated with gas exchange in these forest understorey ferns are in accordance with patterns reported for seed plants, suggesting a high degree of functional constraint on the interrelationships among key elements in foliar design.     

Novel mannose-sequestration technique reveals variation in subcellular orthophosphate pools do not explain the effects of phosphorus nutrition on photosynthesis in Eucalyptus globulus seedlings

Although only a small proportion of plant phosphorus (P) is used for photosynthesis, the relationships between P and photosynthesis can be strong. It was hypothesized, in this study, that variation in the allocation of orthophosphate (Pi) between active (cytoplasmic) and nonactive (vacuolar) pools would underpin differences in rates of photosynthesis in 4-month-old Eucalyptus globulus seedlings grown with a varying P supply. Photosynthetic biochemistry was assessed by the response of net photosynthesis to increasing intercellular [CO2]. Cytoplasmic Pi was sequestered as mannose 6-phosphate. Total P and the proportion of P as Pi were positively related to P supply. The ratios of active : stored Pi (10-24%) varied little over the range of treatments. Active Pi was positively related to P supply, as was photosynthesis (7 micromol CO2 m(-2) s(-1) with 0 mM P vs. 16 micromol CO2 m(-2) s(-1) with 0.32 mM P). Positive relationships between P supply and photosynthesis were explained best by leaf P content, not by active pools of Pi. The distribution of Pi between the vacuole and the cytoplasm had little impact on the photosynthetic phosphorus-use efficiency (PPUE), and reductions in cytoplasmic Pi had little effect on photosynthesis. Hence, PPUE is an unsuitable guide for assessing plant responses to increasingly unavailable P in the environment.     

Predator–prey encounter rates in freshwater piscivores: effects of prey density and water transparency

One of the most fundamental components of predator–prey models is encounter rate, modelled as the product of prey density and search efficiency. Encounter rates have, however, rarely been measured in empirical studies. In this study, we used a video system approach to estimate how encounter rates between piscivorous fish that use a sit-and-wait foraging strategy and their prey depend on prey density and environmental factors such as turbidity. We first manipulated prey density in a controlled pool and field enclosure experiments where environmental factors were held constant. In a correlative study of 15 freshwater lakes we then estimated encounter rates in natural habitats and related the results to both prey fish density and environmental factors. We found the expected positive dependence of individual encounter rates on prey density in our pool and enclosure experiments, whereas the relation between school encounter rate and prey density was less clear. In the field survey, encounter rates did not correlate with prey density but instead correlated positively with water transparency. Water transparency decreases with increasing prey density along the productivity gradient and will reduce prey detection distance and thus predator search efficiency. Therefore, visual predator–prey encounter rates do not increase, and may even decrease, with increasing productivity despite increasing prey densities.     

Effects of resource level and habitat type on behavioral and morphological plasticity in Eurasian perch

Spatial and temporal heterogeneity in the environment is a common feature affecting many natural populations. For example, both the resource levels and optimal habitat choices of individuals likely change over time. One way for organisms to cope with environmental variation is to display adaptive plasticity in traits such as behavior and morphology. Since trait plasticity is hypothesized to be a prerequisite for character divergence, studies of mechanisms behind such plasticity are warranted. In this study, we looked at the interaction of two potentially important environmental variables on behavioral and morphological plasticity in Eurasian perch (Perca fluviatilis L.). More specifically, the plastic responses in activity and morphology of perch exposed to different resource levels and simulated habitat types were studied in an aquarium experiment. The resource level experienced had a large influence on plasticity in both activity and morphology. Behavioral adaptations have been thought to mediate morphological transitions, and we suggest that the morphological response to the resource level was mediated by differences in activity and growth rates. The habitat type also affected morphological plasticity but to a lesser extent, and there was no effect on activity from habitat type. Based on these results, we suggest that it is essential to include several environmental factors acting in concert when studying mechanisms behind trait plasticity. We also propose that variation in resource levels might play a key role in fostering trait plasticity in at least fish populations, while other environmental variables such as divergent habitat complexities and prey types might be less influential. Dynamics in resource levels and optimal habitat choices might thus be important factors influencing character divergence in natural populations.