Actual vs perceived profitability: A study of floral choice of honey bees

The relationship between actual and perceived profitability was investigated by quantifying choice behavior of foraging honey bees (Apis mellifera).Rate of net energy gain was used as a measure of profitability. Individual bees repeatedly chose between a yellow and a blue tubular artificial flower which had different associated profitabilities. Handling costs were manipulated by using flowers of different depth;energy gains were manipulated by using different volumes of a 20% (w/w) sucrose solution. Bees' discrimination between the two flowers increased as the absolute difference in profitabilities increased and discrimination decreased as profitabilities of both flowers increased. Therefore, discrimination depended on the relative difference in profitability between flowers, and therefore, perception was a nonlinear function of actual rates of net energy gain. The results also suggested that motivation to choose between flowers depended on the level of profitability. We suggest that nonlinear perceptual scales and motivation should be incorporated into models of food choice as constraints and should be considered in the design of experiments used to test predictions of models and in the interpretation of experimental results.     

A Markov approach for describing post-fire succession of vegetation

Vegetation dynamics in the coastal area of the Seto Inland Sea region in Japan, where wild fires occur frequently, were described using a stationary Markov model. In this region, vegetation types ofMiscanthus-Pleioblastus grassland,Lespedeza-Mallotus scrub,Pinus-Rhododendron forest andCrassocephalum-Erechtites community have been identified, and these show cyclic succession under the influence of fires. The model uses parameters determining fire frequency and rate of successional change to analyze the effect of variation in these parameters on the areal ratio of each vegetation type at equilibrium and on the time taken for one vegetation type to succeed another (elapsed successional time). The effect of fire frequency differs between hypothetical habitats with high and low productivity. A policy for vegetation management in areas of high and low productivity is proposed. The advantages and limitations of applying Markov models to studies of vegetation succession are also discussed.     

A general principle for the allocation of limited resources

Summary A marginal fitness theorem is derived for the allocation of a limited resource among alternative activities that have effects on the fitness of an individual. The marginal advantage theorem states that at the evolutionarily stable strategy (ESS), the marginal gains from increasing each of the allocations (expressed as partial derivatives of the fitness advantage of a rare mutant) are equal. The theorem is true for all proportional allocations (a + b + c + ...=j), regardless of the number of allocations, the nature of the response curves describing the direct effects of the allocations [f(a), etc.], or the way the effects of different allocations combine into fitness. The theorem is extended to size-number compromises and packaging strategies. The marginal advantage theorem is used to derive general theorems about the marginal effects of allocations [f (a), etc.] at the ESS and matching rules concerned with the total fitness to cost ratios of allocations at the ESS. The marginal advantage theorem is applicable to diverse allocation strategies, and provides a method for obtaining ESS allocations for any number of allocations and their components.     

The effects of feedback lighting on the circadian drinking rhythm in the diurnal new world primate Saimiri sciureus

Feedback lighting provides illumination primarily during the subjective night (i.e., the photosensitive portion of the circadian cycle) in response to a given behavior. This technique has previously been used to test the nonparametric model of entrainment in nocturnal rodents. In three species (Rattus norvegicus, Mesocricetus auratus, and Mus musculus), the free-running period of the locomotor activity rhythm was similar whether the animals were exposed to continuous light or discrete light pulses occurring essentially only during the subjective night (i.e., feedback lighting). In the current experiments, feedback lighting was presented to squirrel monkeys so that light fell predominantly during the subjective night. Feedback lighting was linked to the drinking behavior in this diurnal primate so that when the animal drank, the lights went out. Despite the seemingly adverse predicament, the monkeys maintained regular circadian drinking rhythms. Furthermore, just as the period of the free-running activity rhythms of nocturnal rodents exposed to continuous light or feedback lighting were similar, the period of the drinking rhythms of the squirrel monkeys in continuous light and feedback lighting were comparable (25.6 +/- 0.1 and 25.9 +/- 0.1 hours, respectively), despite a substantial decrease in the total amount of light exposure associated with feedback lighting. The free-running period of monkeys exposed to continuous dark (24.5 +/- 0.1 hours) was significantly shorter than either of the two lighting conditions (P < 0.001). The results presented for the drinking rhythm were confirmed by examination of the temperature and activity rhythms. Therefore, discrete light pulses given predominately during the subjective night are capable of simulating the effects of continuous light on the free-running period of the circadian rhythms of a diurnal primate. The response of squirrel monkeys to feedback lighting thus lends further support for the model and suggests that the major entrainment mechanisms are similar in nocturnal rodents and diurnal primates.     

Degradation of diarylethane structures by Pseudomonas fluorescens biovar I

Pseudomonas fluorescens biovar I was isolated from a pulp mill effluent based on its ability to grow on synthetic media containing 1,2-diarylethane structures as the sole carbon and energy source. Analysis of samples taken from cultures of this strain in benzoin or 4,4-dimethoxybenzoin (anisoin), showed that cleavage between the two aliphatic carbons takes place prior to ring fission. Intermonomeric cleavage was also obtained with crude extracts. Substrates of this reaction were only those 1,2-diarylethane compounds that supported growth of the bacterium. The purification and partial characterization of an enzyme that catalyzes the NADH-dependent reduction of the carbonyl group of benzoin and anisoin is also reported.     

Cannibalism as a life boat mechanism

Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one.     

Structural and functional domains of cellobiohydrolase I from trichoderma reesei

Limited proteolysis (papain) of the cellobiohydrolase I (CBH I, 65 kDa) from Trichoderma reesei led to the seperation of two functional domains: a core protein (55 kDa) containing the active site, and a C-terminal glycopeptide (10 kDa) implicated in binding to the insoluble matrix (cellulose). The quaternary structures of the intact CBH I and its core in solution are now compared by small angle X-ray scattering (SAXS) measurements. The molecular parameters derived for the core (Rg=2.09 nm, D_max=6.5 nm) and for the intact enzyme (Rg=4.27 nm, D_max=18 nm) indicate very different shapes. The resulting models show a tadpole-like structure for the intact enzyme where the isotropic part coincides with the core protein and the flexible tail part should be identified with the C-terminal glycopeptide. Thus in this enzyme, functional differentiation is reflected in structural peculiarities.Abbreviations SAXS small angle X-ray scattering - SDS-PAGE SDS-polyacrylamide gel electrophoresis - IEF-PAG polyacrylamide gel isoelectric focusing; cellobiohydrolase (CBH, 1,4--glucan cellobio hydrolase (E.C.3.2.1.91)) - D_max maximum diameter - Rg radius of gyration     

A model for gramicidin A′-phospholipid interactions in bilayers

A model is proposed for the effect of gramicidin A on the order and structure of phospholipid dispersions. According to this model, the addition of gramicidin A influences the surrounding lipids via two independent mechanisms. The first arises from a drop in surface pressure for those lipids substantially bounded by gramicidin A. The second mechanism arises from the increase in the phospholipid headgroup spacing due to the small polar region of the polypeptide. The model provides an explanation for the currently available NMR, X-ray diffraction and Langmuir monolayer results. The model also suggests mechanisms for the ability of gramicidin A to trigger a transition of the lipid from the lamellar to hexagonal II phase, the dependence of this transition on the lipid chain length and the formation of a lamellar phase with lysophosphatidylcholine.Abbreviations NMR nuclear magnetic resonance - DMPC dimyristoylphosphatidylcholine - S molecular order parameter - CSA chemical shift anisotropy - DPPC dipalmitoylphosphati-dylcholine - LPC lysophosphatidylcholine