Cognitive mechanisms of risky choice: is there an evaluation cost?

We contrast two classes of choice processes, those assuming time-consuming comparisons and those where stimuli for each option act independently, competing for expression by cross censorship. The Sequential Choice Model (SCM) belongs in the latter category, and has received empirical support in several procedures involving deterministic alternatives. Here we test this model in risky choices. In two treatments, each with five conditions, European starlings (Sturnus vulgaris) faced choices between options with unpredictable outcomes and risk-free alternatives. In the delay treatment the five conditions involved choices between a variable option offering two equiprobable delays to reward and a fixed option with delay differing between conditions. The amount treatment was structurally similar, but amount of reward rather than delay was manipulated. As assumed (and required) by the SCM, latency to respond in no-choice trials reflected each option's richness with respect to the background alternatives, and, crucially, preferences in simultaneous choices were predictable from latencies to each option in forced trials. However, we did not detect reliable differences in response times between forced and choice trials, neither the lengthening expected from evaluation models nor the shortening expected from the SCM.     

Choice in multi-alternative environments: A trial-by-trial implementation of the Sequential Choice Model

The sequential choice model (SCM) proposes that latencies to accept options presented alone can be used to predict preferences between these options when they are presented simultaneously. SCM has been proposed and tested in experiments where only two alternatives were present. To further challenge the model, we trained and tested European starlings (Sturnus vulgaris) in an environment with a background of four alternatives differing in delay to reinforcement. Unexpected binary choices between the six possible pairs of alternatives were used to assess preference. The model's predictions of the strength of preference roughly corresponded to the bird's choices for each of the six choice situations. More importantly, a trial-by-trial test of the model correctly predicted 84% of all individual choice trials.     

Factors influencing host choice of the honey bee parasite Varroa jacobsoni Oud

Reproducing Varroa jacobsoni obtained from brood cells of Apis mellifera L. with 13–16 day old bees (pupae) and Varroa mites kept on adult bees for at least 8 days were simultaneously tested for their choice in three host types. Comparisons were made of attractiveness of Varroa jacobsoni to nurse bees, pollen foragers as to larvae from nearly capped brood cells. Host choices were observed in Petri dishes and in an Y-shaped olfactometer. Varroa jacobsoni obtained from capped brood cells showed a stronger preference for nurse bees in Petri dish simultaneous choice tests with pollen foragers or larvae than did mites which were previously kept on adult bees. In olfactometer simultaneous choice tests, the two mite test groups showed no clear difference in preferences for bees of different ages. The preference of Varroa jacobsoni for bees of different ages is therefore not only influenced by host factors but also by intrinsic factors in female mites that depend on the mite's reproductive stage.     

Growth of the Thermophilic Bacterium Geobacillus uralicus as a Function of Temperature and pH: An SCM-Based Kinetic Analysis

The synthetic chemostat model (SCM), originally developed to describe nonstationary growth under widely varying concentrations of the limiting substrate, was modified to account for the effects of nontrophic factors such as temperature and pH. The bacterium Geobacillus uralicus, isolated from an ultradeep well (4680 m), was grown at temperatures ranging from 40 to 75°C and at pH varying from 5 to 9. The biomass kinetics was reasonably well described by the SCM, including the phase of growth deceleration observed in the first hours after a change in the cultivation temperature. At an early stage of batch growth in a neutral or alkalescent medium, bacterial cells showed reversible attachment to the glass surface of the fermentation vessel. The temperature dependence of the maximum specific growth rate (_m) was fitted using the equation _m = Aexp(T)/{1 + expB[1 – C/(T + 273)]}, where A, , B, and C are constants. The maximum specific growth rate of 2.7 h^–1 (generation time, 15.4 min) was attained on a complex nutrient medium (peptone and yeast extract) at 66.5°C and pH 7.5. On a synthetic mineral medium with glucose, the specific growth rate declined to 1.2 h^–1, and the optimal temperature for growth decreased to 62.3°C.     

Quantification of non-Q B -reducing centers in leaves using a far-red pre-illumination

An alternative approach to quantification of the contribution of non-Q_B-reducing centers to Chl a fluorescence induction curve is proposed. The experimental protocol consists of a far-red pre-illumination followed by a strong red pulse to determine the fluorescence rise kinetics. The far-red pre-illumination induces an increase in the initial fluorescence level (F_{25 μs}) that saturates at low light intensities indicating that no light intensity-dependent accumulation of Q_A⁻ occurs. Far-red light-dose response curves for the F_{25 μs}-increase give no indication of superimposed period-4 oscillations. F_{25 μs}-dark-adaptation kinetics following a far-red pre-pulse, reveal two components: a faster one with a half-time of a few seconds and a slower component with a half-time of around 100 s. The faster phase is due to the non-Q_B-reducing centers that re-open by recombination between Q_A⁻ and the S-states on the donor side. The slower phase is due to the recombination between Q_B⁻ and the donor side in active PS II reaction centers. The pre-illumination-induced increase of the F_{25 μs}-level represents about 4–5% of the variable fluorescence for pea leaves (∼2.5% equilibrium effect and 1.8–3.0% non-Q_B-reducing centers). For the other plant species tested these values were very similar. The implications of these values will be discussed.     

Analysis of dark-relaxation kinetics of variable fluorescence in intact leaves

The dark-relaxation kinetics of variable fluorescence, F_v, in intact green leaves of Pisum stativum L. and Dolichos lablab L. were analyzed using modulated fluorometers. Fast (t_1/2 = 1 s) and slow (t_1/2 = 7–8 s) phases in f_v dark-decay kinetics were observed; the rate and the relative contribution of each phase in total relaxation depended upon the fluence rate of the actinic light and the point in the induction curve at which the actinic light was switched off. The rate of the slow phase was accelerated markedly by illumination with far-red light; the slow phase was abolished by methyl viologen. The halftime of the fast phase of F_v dark decay decreased from 250 ms in dark-adapted leaves to 12–15 ms upon adaptation to red light which is absorbed by PSII. The analysis of the effect of far-red light, which is absorbed mainly by PSI, on F_v dark decay indicates that the slow phase develops when a fraction of Q_A ^– (the primary stable electron acceptor of PSII) cannot transfer electrons to PSI because of limitation on the availability of P700⁺ (the primary electron donor of PSI). After prolonged illumination of dark-adapted leaves in red (PSII-absorbed) light, a transient. F_v rise appears which is prevented by far-red (PSI-absorbed) light. This transient f_v rise reflects the accumulation of Q_A ^– in the dark. The observation of this transient F_v rise even in the presence of the uncoupler carbonylcyanide m-chlorophenyl hydrazone (CCCP) indicates that a mechanism other than ATP-driven back-transfer of electrons to QA may be responsible for the phenomenon. It is suggested that the fast phase in F_v dark-decay kinetics represents the reoxidation of Q_A ^– by the electron-transport chain to PSI, whereas the slow phase is likely to be related to the interaction of Q_A ^– with the donor side of PSII.Abbreviations CCCP carbonylcyanide m-chlorophenylhydrazone - F_O initial fluorescence level - F_v variable fluorescence - P700 primary electron donor of PSI - PSI, II photosystem I, II - Q_A (Q_A ^–) Q_B (Q_B ^–) primary and secondary stable electron acceptor of PSII in oxidized (reduced) state Supported by grant B6.1/88 DST, Govt. of India.     

Role of cooperative H(+)/e(-) linkage (redox bohr effect) at heme a/Cu(A) and heme a(3)/Cu(B) in the proton pump of cytochrome c oxidase

It is a pleasure to contribute to the special issue published in honor of Vladimir Skulachev, a distinguished scientist who greatly contributes to maintain a high standard of biochemical research in Russia. A more particular reason can be found in his work (Artzabanov, V. Y., Konstantinov, A. A., and Skulachev, V. P. (1978) FEBS Lett., 87, 180–185), where observations anticipating some ideas presented in my article were reported. Cytochrome c oxidase exhibits protonmotive, redox linked allosteric cooperativity. Experimental observations on soluble bovine cytochrome c oxidase are presented showing that oxido-reduction of heme a/Cu_A and heme a ₃/Cu_B is linked to deprotonation/protonation of two clusters of protolytic groups, A₁ and A₂, respectively. This cooperative linkage (redox Bohr effect) results in the translocation of 1 H⁺/oxidase molecule upon oxido-reduction of heme a/Cu_A and heme a ₃/Cu_B, respectively. Results on liposome-reconstituted oxidase show that upon oxidation of heme a/Cu_A and heme a ₃/Cu_B protons from A₁ and A₂ are released in the outer aqueous phase. A₁ but not A₂ appears to take up protons from the inner aqueous space upon reduction of the respective redox center. A cooperative model is presented in which the A₁ and A₂ clusters, operating in close sequence, constitute together the gate of the proton pump in cytochrome c oxidase.Translated from Biokhimiya, Vol. 70, No. 2, 2005, pp. 220–230.Original Russian Text Copyright © 2005 by Papa.This revised version was published online in April 2005 with corrections to the post codes.     

Electron transfer in deuterated reaction centers of Rhodobacter sphaeroides at 90 K according to femtosecond spectroscopy data

The primary act of charge separation was studied in P⁺B_A ^– and P⁺H_A ^– states (P, primary electron donor; B_A and H_A, primary and secondary electron acceptor) of native reaction centers (RCs) of Rhodobacter sphaeroides R-26 using femtosecond absorption spectroscopy at low (90 K) and room temperature. Coherent oscillations were studied in the kinetics of the stimulated emission band of P* (935 nm), of absorption band of B_A ^– (1020 nm) and of absorption band of H_A (760 nm). It was found that in native RCs kept in heavy water (D₂O) buffer the isotopic decreasing of basic oscillation frequency 32 cm ^–1 and its overtones takes place by the same factor 1.3 in the 935, 1020, and 760 nm bands in comparison with the samples in ordinary water H₂O. This suggests that the femtosecond oscillations in RC kinetics with 32 cm ^–1 frequency may be caused by rotation of hydrogen-containing groups, in particular the water molecule which may be placed between primary electron donor P_B and primary electron acceptor B_A. This rotation may appear also as high harmonics up to sixth in the stimulated emission of P*. The rotation of the water molecule may modulate electron transfer from P* to B_A. The results allow for tracing of the possible pathway of electron transfer from P* to B_A along a chain consisting of polar atoms according to the Brookhaven Protein Data Bank (1PRC): Mg(P_B)-N-C-N(His M200)-HOH-O = B_A. We assume that the role of 32-cm ^–1 modulation in electron transfer along this chain consists of a fixation of electron density at B_A ^– during a reversible electron transfer, when populations of P* and P⁺B_A ^– states are approximately equal.     

Spectroscopic studies of bound cytochrome c and an iron-sulfur center in a purified reaction center complex from the green sulfur bacterium Chlorobium tepidum

Flash-induced optical kinetics at room temperature of cytochrome (Cyt) c ₅₅₁ and an Fe-S center (CF_A/CF_B) bound to a purified reaction center (RC) complex from the green sulfur photosynthetic bacterium Chlorobium tepidum were studied. At 551 nm, the flash-induced absorbance change decayed with a t _1/2 of several hundred ms, and the decay was accelerated by 1-methoxy-5-methylphenazinium methyl sulfate (mPMS). In the blue region, the absorbance change was composed of mPMS-dependent (Cyt) and mPMS-independent component (CF_A/CF_B) which decayed with a t _1/2 of 400–650 ms. Decay of the latter was effectively accelerated by benzyl viologen (Em –360 mV) and methyl viologen (–440 mV), and less effectively by triquat (–540 mV). The difference spectrum of Cyt c had negative peaks at 551, 520 and 420 nm, with a positive rise at 440 to 500 nm. The difference spectrum of CF_A/CF_B resembled P430 of PSI, and had a broad negative peak at 430435 nm.Abbreviations (B)Chl (bacterio)chlorophyll - Cyt cytochrome - F_A, F_B and F_X iron-sulfur center A, B and X of Photosystem I - CF_A, CF_B and CF_X F_A-,F_B- and F_X-like Fe-S center of Chlorobium - mPMS 1-methoxy-5-methylphenazinium methyl sulfate - PSI Photosystem I - RC reaction center     

Effects of pH and light on the membrane conductance measured in the acid and basic zones ofChara

Summary The area-specific coductance of the membrane in the acid and basic zones (denoted byG _A andG _B , respectively) ofChara cells was measured in flowing solutions, containing 5mm zwitterionic buffer, as a function of the external pH(denoted by pH⁰). During illuminationG _A was 1 S/m² for pH⁰ in the range 5 to 8.5, and increased markedly to 3 to 6 S/m² at higher pH₀.G _B , however, was always larger thanG _A during illumination with a typical magnitude of 5 to 15 S/m² for pH⁰ 6 to 12. Thus under many experimental conditions it is possible that there is no single correct value for the membrane area-specific conductance. A flow of current in the external medium between the acid and basic regions was found to be associated with pH banding, and also withG _B exceedingG _A . This current could be present in flowing solutions without added HCO ₃ ^– over a wide range of pH⁰ and at high (25mm) buffer concentration. Combining measurements ofG _A andG _B with measurements of the currents in the acid and basic zones (denoted byJ _A andJ _B , respectively), it was estimated that the resting (i.e. in the absence of net current flow) potential difference (PD) across the membranes within the individual zones (denoted byU _A andU _B ) was –265±20 and –183±5 mV, respectively, during illumination. Upon the removal of illumination at pH⁰-7.5,G _A ,G _B andJ _B were found to decrease rapidly during the initial few hundred seconds. During this period (U _B –V _m ) remained relatively constant. A transient hyperpolarization ofV _m often occurred, the magnitude of which was correlated with the magnitude ofJ _B prior to the removal of illumination. After some 0.5 to 1 ksec of darkness,G _A andG _B had both decreased considerably and nowG _A G _B andU _A U _B V _m . Eventually, after 2 to 8 ksec of darkness, the membrane conductance was effectively homogeneous with a much smaller magnitude (typically<0.2S/m²) andV _m was depolarized by typically 5 to 15 mV.     

Expression of multiple insecticidal genes confers broad resistance against a range of different rice pests

We report the simultaneous introduction of three insecticidal genes (the Bt genes cry1Ac and cry2A, and the snowdrop lectin gene gna) into commercially important indica rice varieties M7 and Basmati 370, by particle bombardment. Transgenic plants expressed Cry1Ac, Cry2A and GNA at different levels, either singly or in combination at 0.03–1%, 0.01–0.5% and 0.01–2.5% of total soluble protein, respectively. The transgenes showed stable transmission and expression, and R₁ transgenic plants provided significant (p<0.01) protection against three of the most important insect pests of rice: rice leaf folder (Cnaphalocrocis medinalis), yellow stemborer (Scirpophaga incertulas) and brown planthopper (Nilaparvata lugens). The triple transformants showed significantly (p<0.05) higher resistance to these insects than plants expressing single transgenes. Bioassays using the triple-transgenic plants showed 100% eradication of the rice leaf folder and yellow stem borer, and 25% reduction in the survival of the brown planthopper. The greatest reduction in insect survival, and the greatest reduction in plant damage, occurred in plants expressing all three transgenes. This approach maximises the utility of gene transfer technology to introduce combinations of genes whose products disrupt different biochemical or physiological processes in the same insect, providing a multi-mechanism defence.     

Induced accumulation of triterpenoids in Scutellaria baicalensis suspension cultures using a yeast elicitor

When growth-phase cell suspension cultures of Scutellaria baicalensis were treated with 50 g of yeast elicitor preparation ml^–1, both oleanolic acid and ursolic acid transiently increased in the culture medium rather than in the cells. The maximal triterpenoid concentration was 13.7 mg l^–1 media approx. 35 h after treatment, whereas the maximum concentration was 2.1 mg l^–1 media after about 20 h following treatment with methyl jasmonate. Elicitor treatment also doubled phospholipase A₂ activity (25 pmol mg^–1 min) and the simultaneous treatment of aristolochic acid, a phospholipase A₂ inhibitor, inhibited triterpenoids accumulation as well as phospholipase A₂ activity.     

Orientation of reaction center complexes fromRhodobacter sphaeroides in proteoliposomes and the effect ofo-phenanthroline on electrogenesis during primary photochemical reaction

The orientation ofRhodobacter sphaeroides reaction center complexes (RC complexes) in proteoliposomal membranes was investigated by a direct electrometric method. Conditions were found that allow monitoring of only that RC complex fraction that is oriented with its donor side to the inner part of the proteoliposome. It is shown thato-phenanthroline, an inhibitor of electron transfer between primary (Q_A) and secondary (Q_B) quinone acceptors, can also inhibit the photoinduced Q_A reduction. The efficiency of this inhibition depends on the concentration of added ubiquinone. It is assumed that the laser flash-inducedo-phenanthroline inhibition of primary dipole (P-870⁺ · Q _A ^– ) formation is of a competitive nature.     

Age-Related Changes in Turn–Amplitude Characteristics of the EMG Recorded during Graded Isometric Contraction

The number of turns, the mean amplitude, and the peak ratio of the electromyogram (EMG) recorded in m. biceps brachii at different levels of isometric contraction were analyzed in nine age groups (from 1 month to 72 years, N = 192). Regression equations describing the age-related changes in number of EMG turns and mean EMG amplitude were respectively y = –A(2.48 ± 0.14) – M(1.32 ± 0.17) + B(11.02 ± 0.68) + (194.71 ± 7.81) (P < 0.001) and y = –A(2.47 ± 0.19) – M(1.87 ± 0.23) + B(10.03 ± 0.88) + (321.57 ± 11.05) (P < 0.001), where A is the age, years; M is the body mass, kg; and B is the load, kg. With increasing age, the interference EMG tended to assume a so-called neurogenic form as a result of age-specific organization of motor functions at the segmental level.     

Influence of operational parameters in the flocculation and production ofLactobacillus plantarum

Summary The influence of different operational parameters, such as the dilution rate (D) and the bleeding rate (B), in the production of a flocculent strain ofLactobacillus plantarum was studied. The effect of the dilution rate was demonstrated to be related to the lactic acid concentration inside the reactor. The effect of the bleeding rate was shown to be critical in the stabilization of the operation (due to a better pH control). It also allowed a continuous recovery of cells outside the reactor. Viability testing of the lactic starter cultures showed that operation with cell purge increased the viability of the starter cultures obtained.Nomenclature B Bleeding rate, h^–1 - D Dilution rate, h^–1 - F Feed flow rate, L h^–1 - I Feed velocity, m h^–1 - Specific growth rate, h^–1 - v Lactic acid specific productivity, g g^–1 h^–1 - P Product concentration (lactic acid), g L^–1 - P _out Product concentration leaving the system, g L^–1 - Q _b Bleeding flow rate, L h^–1 - R Recirculation velocity, m h^–1 - S Substract concentration, g L^–1 - t Time, h - T _p Time of ascensional flow (length of the column/total ascensional velocity), h - T _r Residence time (1/D), h - V Volume of the reactor, L - X Cell concentration, g L^–1 - X _out Cell concentration leaving the system, g L^–1     

Determination of Homalodisca coagulata (Hemiptera: Cicadellidae) egg ages suitable for oviposition by Gonatocerus ashmeadi, Gonatocerus triguttatus, and Gonatocerus fasciatus (Hymenoptera: Mymaridae)

Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) eggs 1–10 days of age were exposed to Gonatocerus ashmeadi Girault, Gonatocerus triguttatus Girault, and Gonatocerus fasciatus Girault (all Hymenoptera: Mymaridae) in no choice laboratory trials to investigate egg age utilization and to determine which egg ages are vulnerable to attack by these three parasitoids. The H. coagulata egg ages that were most suitable for oviposition by G. ashmeadi, G. triguttatus, and G. fasciatus were eggs 3, 4, and 2 days of age, respectively. Egg ages least suitable for parasitoid development were 6–10 days for G. ashmeadi (resulting in <50% parasitism), 1–2 and 7–10 days for G. triguttatus (resulting in <25% parasitism), and 3–10 days for G. fasciatus (resulting in <11% parasitism). Pooling parasitism data across all egg ages showed that parasitism by G. ashmeadi was 12.9 and 28.5% higher compared with G. triguttatus and G. fasciatus, respectively, and G. triguttatus resulted in 15.6% higher percentage parasitism compared with G. fasciatus. Egg age had a significant effect on the percentage of female G. ashmeadi offspring produced, but this was not significant for G. triguttatus, and low G. fasciatus parasitism prevented statistical analyses for comparisons. Results from tests where females were offered a choice for oviposition between eggs 1, 3, and 5 days of age demonstrated that G. ashmeadi and G. triguttatus showed no significant oviposition preference, while percentage parasitism by G. fasciatus was 29.4 and 7.4% higher when females were presented eggs 1 and 3 days of age, respectively, compared with eggs 5 days of age. Choice tests indicated that an overlap in egg age suitability for oviposition exists between G. ashmeadi, G. triguttatus, and G. fasciatus, and that interspecific competition for eggs 1, 2, and 3 days of age may occur in the field environment.     

Limits on asymmetric orthopositronium formation in high Z optically active molecules

The proposed connection between the parity violating handedness of beta particles in radioactive decay and the sign (L) of biological chirality (the Vester-Ulbricht [V-U] hypothesis) is experimentally tested. The theoretically predicted asymmetry in triplet positronium formation (A _Ps) is measured in several highZ optically active molecules using low energy positrons with a net helicity. We findA _Ps<3×10^–4 in selenocystine (Z=34) and thyroxine (Z=53), excluding part of the theoretically predicted range of 4×10^–3> A _Ps>2×10^–6 in these molecules. The connection between these limits and limits on asymmetric radiolysis (A _R) is made, with a new limit ofA _R>10^–9 being placed. This limit onA _R, which is thirty times lower than a previous measurement in the amino acid leucine (Z=6), is still not small enough to rule out the V-U hypothesis.     

Habitat and sediment preferences ofAxarus festivus larvae

During fall draw-down of a reservoir in northeast Kansas it was observed that larvae ofAxarus festivus were restricted to highly weathered Pennsylvanian Shale outcrops and surrounding coarse sediments with high-clay content derived from erosion of the shale outcroppings. Larvae constructed burrows into the outcrops and eroded coarse sediments, which they used to filter feed by setting up currents through the burrows. Burrows were widely distributed over the outcrops, with average densities ranging from 372–2,351 burrows m^–2. However, closer inspection revealed that burrows were more common at apices of individual shale strata, where weathering of the outcrop was most advanced. Here burrows were more uniformly distributed and densities ranged to 4,166 burrows m^–2. 73% of burrows contained larvae. Burrows were generally U-shaped, and averaged 1.8 mm in diameter and 42 mm in total length. Laboratory experiments revealed that 4th instar larvae removed from burrows could construct new burrows in weathered shale, but preferentially used old empty burrows if available. When given choices among alternative sediment combinations of sandvs. finely-ground shale, sandvs. coarsely-ground shale, and finely-ground shalevs. coarsely-ground shale, larvae exhibited statistically significant preferences for the finely-ground shales (P<0.001), coarsely-ground shales (P<0.001), and coarsely-ground shales (P<0.01), respectively. It is concluded that larvae (1) actively select shale or high-clay content sediments, (2) can differentiate among sediments with differing physical properties and (3) exhibit behavioral choices for sediment types that guide them toward shale outcrops.     

Effects of downcomer-to-riser cross sectional area ratio on operation behaviour of external-loop airlift bioreactors

Experiments performed in two external-loop airlift bioreactors of laboratory and pilot scale, (1.880–1.189) · 10^–3 m³ and (0.170-0.157)m³, respectively, are reported. The A _D /A _R ratio was varied between 0.111–1.000 and 0.040–0.1225 in the laboratory and pilot contractor respectively.Water and solutions of different coalescence (2-propanol 2% vol, 1 M Na (glucose 50% wt/vol) and rheological behaviour (non-Newtonian starch solutions with consistency index K=0.061–3.518 Pas ⁿ and flow behaviour index n=0.86-0.39), respectively, were used as liquid phase. Compressed air at superficial velocities v _SGR =0.016–0.178 ms^–1 in the laboratory contactor and v _SGR =0.010–0.120 ms^–1 in the pilot contactor, respectively was used as gaseous phase.The A _D /A _R ratio affect gas-holdup behaviour as a result of the influence of A _D /A _R on liquid circulation velocity.Experimental results show that A _D /A _R ratio affect circulation liquid velocity by modifying he resistence to flow and by varying the fraction of the total volume contained in downcomer and riser. A _D /A _R ratio has proven to be the main factor which determines the friction in the reactor. Mixing time increases with increasing of the reactor size and decreases with A _D /A _R decreasing.The volumetric gas-liquid mass transfer coefficient increases with A _D /A _R ratio decreasing, as a result of variations of the liquid velocity with A _D /A _R , which affect interfacial areas.Correlations applicable to the investigated contactors have been presented, together with the fit of some experimental data to existing correlation in literature.List of Symbols A _D downcomer cross sectional area (m²) - A _R riser cross sectional area (m²) - a coefficient in Eq. (9) (-) - a _L gas-liquid interfacial area per unit volume (m^–1) - b coefficient in Eq. (9) (-) - C tracer concentration (kg m^–3) - C tracer concentration at the state of complete mixing (kg m^–3) - c coefficient in Eq. (12) - c _S coefficient in Eq. (5) - D _D downcomer diameter (m) - D _R riser diameter (m) - d _B bubble size (m) - H _D downcomer height (m) - H _d dispersion height (m) - H _L gas-free liquid height (m) - H _R riser height (m) - I inhomogeneity (-) - K consistency index (Pa s ⁿ ) - k _L a volumetric gas-liquid oxygen mass transfer coefficient (s^–1) - m exponent in Eq. (12) (-) - n flow behaviour index (-) - P _G power input due to gassing (W) - t _M mixing time (s) - V _A connecting pipe volume (m³) - V _D downcomer volume (m³) - V _d volume of dispersion (m³) - V _R riser volume (m³) - V _T total reactor liquid volume (m³) - v _SGR riser gas superficial velocity (m s^–1) - _GR riser gas holdup (-) - shear rate (m s^–1) - _app apparent viscosity (Pa s) - shear stress     

Rationality in risk-sensitive foraging choices by starlings

Normative models of choice usually predict preferences between alternatives by computing their value according to some criterion, then identifying the alternative with greatest value. An important consequence of this procedure is captured in the economic concept of rationality, defined through a number of principles that are necessary for the existence of an ordinal scale of value upon which organisms base their choices. Violations of these principles, such as some recently reported breaches of transitivity and regularity in birds and honeybees, have strong implications for the understanding of decision mechanisms in humans and nonhumans alike. We investigated rationality in risky choice using European starlings, Sturnus vulgaris. Birds had to choose between two or three food sources, each associated with a different variance in delay to reward. In three experiments, starlings were strongly risk prone, showing regular and consistent preferences in binary and trinary choices. Preferences also satisfied weak and strong stochastic transitivity. Our results extend the generality of previous research in risk-sensitive foraging to situations where more than two alternatives are present and suggest that violations of rationality in risk-sensitive choices may be expressed only under restricted sets of conditions. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.