Context-dependent foraging decisions in rufous hummingbirds

A core assumption implicit in economic models of animal choice is that subjects assign absolute utilities to options that are independent of the type and number of alternatives available. Humans sometimes appear to violate this assumption and employ relative, as opposed to absolute, currencies when making choices. Recent evidence suggests that animals too might sometimes employ relative choice mechanisms. We tested this idea by measuring the foraging preferences of rufous hummingbirds (Selasphorus rufus) faced with choices analogous to those in which human use of relative currencies is evident. The birds experienced three treatments: a binary choice between two artificial flower types designated concentration (20 microl, 40% sucrose solution) and volume (40 microl, 20%), and two trinary treatments in which a third decoy option (either concentration decoy: 10 microl, 30% or volume decoy: 30 microl, 10%) was added to the set. The birds' preferences differed significantly across the three treatments. In the trinary treatments, the effect of the decoy options was to increase the preference for the option that dominated the decoy. These results are similar to those reported in the human choice literature, and are compatible with the hummingbirds using a relative evaluation mechanism in decision making.     

Context-dependent foraging choices in risk-sensitive starlings

Existing models of risk-sensitive foraging assume that animals assign value to different options according to an absolute currency. It follows from this assumption that choices are expected to be both transitive and regular, because the value assigned to an option is independent of its context. I tested these predictions by comparing preferences obtained in binary and trinary contexts. European starlings, Sturnus vulgaris, were trained using an operant paradigm to forage for three options: Constant (C) that provided a fixed number of food pellets; Low variance (L) with a coefficient of variation of 71% in the number of pellets; High variance (H) with a coefficient of variation of 106%. The preferences of the birds were tested in three binary choice treatments (CL, CH, LH) and one trinary choice treatment (CLH). Overall, there was no evidence for violations of either transitivity or regularity. However, overall, a bird's relative preference for its most preferred option over its second most preferred option was significantly greater in the trinary treatment than in the comparable binary treatment. This effect of context on choice is compatible with starlings' use of comparative instead of absolute currencies in decision making. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Context-dependent decisions among options varying in a single dimension

Contrary to theories of rational choice, adding alternatives to a choice set can change the choices made by both humans and animals. This is usually done by adding an inferior decoy to a choice set of two favoured options that are characterized on two distinct dimensions. We presented wild, free-living rufous hummingbirds (Selasphorus rufus) with choices between two or three options that varied in a single dimension only. The options varied in concentration, in volume or in corolla length. When the options varied in concentration, the addition of a medium option to a choice set of a low and a high concentration caused birds to increase their preference for the high option. However, they decreased their preference for the high concentration option when a low option was added to a choice set of high and medium concentrations. When the options varied only in volume, the addition of a high volume option to a choice set of low and medium options decreased the birds’ preference for the medium option. We saw no effects of adding a third option when the options varied in corolla length alone. Hummingbirds, then, make context-dependent decisions even when the options vary in only a single dimension although which effect occurs seems to depend on the dimension being manipulated. None of the current theories alone adequately explain these results.     

A range-normalization model of context-dependent choice: a new model and evidence

Most utility theories of choice assume that the introduction of an irrelevant option (called the decoy) to a choice set does not change the preference between existing options. On the contrary, a wealth of behavioral data demonstrates the dependence of preference on the decoy and on the context in which the options are presented. Nevertheless, neural mechanisms underlying context-dependent preference are poorly understood. In order to shed light on these mechanisms, we design and perform a novel experiment to measure within-subject decoy effects. We find within-subject decoy effects similar to what have been shown previously with between-subject designs. More importantly, we find that not only are the decoy effects correlated, pointing to similar underlying mechanisms, but also these effects increase with the distance of the decoy from the original options. To explain these observations, we construct a plausible neuronal model that can account for decoy effects based on the trial-by-trial adjustment of neural representations to the set of available options. This adjustment mechanism, which we call range normalization, occurs when the nervous system is required to represent different stimuli distinguishably, while being limited to using bounded neural activity. The proposed model captures our experimental observations and makes new predictions about the influence of the choice set size on the decoy effects, which are in contrast to previous models of context-dependent choice preference. Critically, unlike previous psychological models, the computational resource required by our range-normalization model does not increase exponentially as the set size increases. Our results show that context-dependent choice behavior, which is commonly perceived as an irrational response to the presence of irrelevant options, could be a natural consequence of the biophysical limits of neural representation in the brain.     

Energetic state during learning affects foraging choices in starlings

We investigated the influence of energetic state at the timeof acquaintance with a new food source on preference for thatsource on later encounters, using wild-caught European starlingsas subjects. Twelve birds learned to obtain food rewards bypecking at either of two keys identified by color. The keyswere encountered in different sessions, while the subjects werefood deprived or prefed. Food rewards from both sources werealways identical. After an equal number of reinforced trialswith each source, the birds were presented with choices betweenthem. The birds significantly preferred the source that hadpreviously delivered food under higher deprivation. We relatethese results to findings reported elsewhere of preferencesfor options previously associated with greater effort. We hypothesizethat subjects may attribute value to an option according tothe marginal fitness gain associated with this option in thepast. Although this process may be adaptive under many circumstances,it violates the assumptions of normative models of choice thatimply mechanisms of valuation sensitive to the absolute propertiesof a payoff or to expected absolute changes in state.     

Starlings uphold principles of economic rationality for delay and probability of reward

Rationality principles are the bedrock of normative theories of decision-making in biology and microeconomics, but whereas in microeconomics, consistent choice underlies the notion of utility; in biology, the assumption of consistent selective pressures justifies modelling decision mechanisms as if they were designed to maximize fitness. In either case, violations of consistency contradict expectations and attract theoretical interest. Reported violations of rationality in non-humans include intransitivity (i.e. circular preferences) and lack of independence of irrelevant alternatives (changes in relative preference between options when embedded in different choice sets), but the extent to which these observations truly represent breaches of rationality is debatable. We tested both principles with starlings (Sturnus vulgaris), training subjects either with five options differing in food delay (exp. 1) or with six options differing in reward probability (exp. 2), before letting them choose repeatedly one option out of several binary and trinary sets of options. The starlings conformed to economic rationality on both tests, showing strong stochastic transitivity and no violation of the independence principle. These results endorse the rational choice and optimality approaches used in behavioural ecology, and highlight the need for functional and mechanistic enquiring when apparent violations of such principles are observed.     

Response bias is unaffected by delay length in a delay discounting paradigm

This study examined the contribution of response bias to measures of delay discounting in Long-Evans rats (n = 8) using the adjusting amount procedure. Under this procedure, we assessed preference for 150 μl of 10% sucrose solution delivered following a delay over a variable-amount alternative delivered immediately. Bias was calculated based on relative preference when reinforcers were delivered immediately from both alternatives. We extended this assessment procedure to examine preference when rewards from both alternatives were equally delayed (2, 4, 8, or 16 s) in addition to assessing a traditional delay discounting function. Relative preference was similar across delays and slightly larger than 150 μl. These results indicate that response bias was stable and suggests a relative aversion for the adjusting alternative, which may be due to the variability in reward size associated with that alternative.     

Irrational decision-making in an amoeboid organism: transitivity and context-dependent preferences

Most models of animal foraging and consumer choice assume that individuals make choices based on the absolute value of items and are therefore ‘economically rational’. However, frequent violations of rationality by animals, including humans, suggest that animals use comparative valuation rules. Are comparative valuation strategies a consequence of the way brains process information, or are they an intrinsic feature of biological decision-making? Here, we examine the principles of rationality in an organism with radically different information-processing mechanisms: the brainless, unicellular, slime mould Physarum polycephalum. We offered P. polycephalum amoebas a choice between food options that varied in food quality and light exposure (P. polycephalum is photophobic). The use of an absolute valuation rule will lead to two properties: transitivity and independence of irrelevant alternatives (IIA). Transitivity is satisfied if preferences have a consistent, linear ordering, while IIA states that a decision maker''s preference for an item should not change if the choice set is expanded. A violation of either of these principles suggests the use of comparative rather than absolute valuation rules. Physarum polycephalum satisfied transitivity by having linear preference rankings. However, P. polycephalum''s preference for a focal alternative increased when a third, inferior quality option was added to the choice set, thus violating IIA and suggesting the use of a comparative valuation process. The discovery of comparative valuation rules in a unicellular organism suggests that comparative valuation rules are ubiquitous, if not universal, among biological decision makers.     

Role of decoy molecules in neuronal ischemic preconditioning

AimsDecoy receptors bind with TNF related apoptosis inducing ligands (TRAIL) but do not contain the cytoplasmic domains necessary to transduce apoptotic signals. We hypothesized that decoy receptors may confer neuronal protection against lethal ischemia after ischemic preconditioning (IPC).Main methodMixed cortical neurons were exposed to IPC one day prior to TRAIL treatment or lethal ischemia.Key findingsIPC increased decoy receptor but reduced death receptor expression compared to lethal ischemia. IPC-induced increase in decoy receptor expression was reduced by prior treatment with CAPE, a nuclear factor-kappa B inhibitor (NFκB).SignificanceExpression of decoy molecules, dependent on NFκB, may mediate neuronal survival induced by IPC.     

Disentangling olfactory and visual information used by field foraging birds

Foraging strategies of birds can influence trophic plant–insect networks with impacts on primary plant production. Recent experiments show that some forest insectivorous birds can use herbivore‐induced plant volatiles (HIPVs) to locate herbivore‐infested trees, but it is unclear how birds combine or prioritize visual and olfactory information when making foraging decisions. Here, we investigated attraction of ground‐foraging birds to HIPVs and visible prey in short vegetation on farmland in a series of foraging choice experiments. Birds showed an initial preference for HIPVs when visual information was the same for all choice options (i.e., one experimental setup had all options with visible prey, another setup with hidden prey). However, if the alternatives within an experimental setup included visible prey (without HIPV) in competition with HIPV‐only, then birds preferred the visual option over HIPVs. Our results show that olfactory cues can play an important role in birds’ foraging choices when visual information contains little variation; however, visual cues are preferred when variation is present. This suggests certain aspects of bird foraging decisions in agricultural habitats are mediated by olfactory interaction mechanisms between birds and plants. We also found that birds from variety of dietary food guilds were attracted to HIPVs; hence, the ability of birds to use plant cues is probably more general than previously thought, and may influence the biological pest control potential of birds on farmland.     

From Guard to Decoy: a new model for perception of plant pathogen effectors

The Guard Model for disease resistance postulates that plant resistance proteins act by monitoring (guarding) the target of their corresponding pathogen effector. We posit, however, that guarded effector targets are evolutionarily unstable in plant populations polymorphic for resistance (R) genes. Depending on the absence or presence of the R gene, guarded effector targets are subject to opposing selection forces (1) to evade manipulation by effectors (weaker interaction) and (2) to improve perception of effectors (stronger interaction). Duplication of the effector target gene or independent evolution of a target mimic could relax evolutionary constraints and result in a decoy that would be solely involved in effector perception. There is growing support for this Decoy Model from four diverse cases of effector perception involving Pto, Bs3, RCR3, and RIN4. We discuss the differences between the Guard and Decoy Models and their variants, hypothesize how decoys might have evolved, and suggest ways to challenge the Decoy Model.     

Optimal behaviour can violate the principle of regularity

Understanding decisions is a fundamental aim of behavioural ecology, psychology and economics. The regularity axiom of utility theory holds that a preference between options should be maintained when other options are made available. Empirical studies have shown that animals violate regularity but this has not been understood from a theoretical perspective, such decisions have therefore been labelled as irrational. Here, I use models of state-dependent behaviour to demonstrate that choices can violate regularity even when behavioural strategies are optimal. I also show that the range of conditions over which regularity should be violated can be larger when options do not always persist into the future. Consequently, utility theory—based on axioms, including transitivity, regularity and the independence of irrelevant alternatives—is undermined, because even alternatives that are never chosen by an animal (in its current state) can be relevant to a decision.     

Cytokine decoy and scavenger receptors as key regulators of immunity and inflammation

IL-1R2 was the first decoy receptor to be described. Subsequently receptors which act as pure decoys or scavengers or trigger dampening of cytokine signaling have been described for cytokines and chemokines. Here we review the current understanding of the mode of action and significance in pathology of the chemokine atypical receptor ACKR2, the IL-1 decoy receptor IL-1R2 and the atypical IL-1 receptor family IL-1R8. Decoy and scavenger receptors with no or atypical signaling have emerged as a general strategy conserved in evolution to tune the action of cytokines, chemokines and growth factors.     

Violations of transitivity under fitness maximization

We present a novel demonstration that violations of transitive choice can result from decision strategies that maximize fitness. Our results depend on how the available options, including options not currently chosen, influence a decision-maker's expectations about the future. In particular, they depend on how the presence of an option may act as an insurance against a run of bad luck in the future.     

Natural selection can favour ‘irrational’ behaviour

Understanding decisions is the fundamental aim of the behavioural sciences. The theory of rational choice is based on axiomatic principles such as transitivity and independence of irrelevant alternatives (IIA). Empirical studies have demonstrated that the behaviour of humans and other animals often seems irrational; there can be a lack of transitivity in choice and seemingly irrelevant alternatives can alter decisions. These violations of transitivity and IIA undermine rational choice theory. However, we show that an individual that is maximizing its rate of food gain can exhibit failure of transitivity and IIA. We show that such violations can be caused because a current option may disappear in the near future or a better option may reappear soon. Current food options can be indicative of food availability in the near future, and this key feature can result in apparently irrational behaviour.     

Development of an enzymatic chromatography strip with nicotinamide adenine dinucleotide–tetrazolium coupling reactions for quantitative l-lactate analysis

In this study, a dry assay of l-lactate via the enzymatic chromatographic test (ECT) was developed. An l-lactate dehydrogenase plus a nicotinamide adenine dinucleotide (NADH) regeneration reaction were applied simultaneously. Various tetrazolium salts were screened to reveal visible color intensities capable of determining the lactate concentrations in the sample. The optimal analysis conditions were as follows. The diaphorase (0.5 μl, 2⁻⁶ U/μl) was immobilized in the test line of the ECT strip. Nitrotetrazolium blue chloride (5 μl, 12 mM), l-lactate dehydrogenase (1 μl, 0.25 U/μl), and NAD⁺ (2 μl, 1.5 × 10⁻⁵ M) were added into the mobile phase (100 μl) composed of 0.1% (w/w) Tween 20 in 10 mM phosphate buffer (pH 9.0), and the process was left to run for 10 min. This detection had a linear range of 0.039 to 5 mM with a detection limit of 0.047 mM. This quantitative analysis process for l-lactate was easy to operate with good stability and was proper for the point-of-care testing applications.     

Assessing aural and visual cueing as tools for seabird management

Social attraction, that is, mimicking of active and productive colonies via audio playback of calls of breeding conspecifics and the use of decoys, is commonly used to attract birds to newly established or restored breeding sites. However, little is known about the relative importance of aural versus visual cues for identify nesting areas. Such information is important for design and evaluation of management protocols. We studied the effectiveness of decoys (visual cues) and playbacks (audio cues) as methods for restoring a colony of common terns (Sterna hirundo) at Muskeget Island, Massachusetts, USA. We used a 2-year, crossover experiment with 3 treatment areas: audio and visual, audio only, and visual only. We reversed treatment areas in the second year to control for previous nesting area or substrate preference. In both years, nests were built 9–101 m downwind of loudspeakers. There was no overlap in areas used for nesting between years and no nests were built within decoy plots in either year. Behavioral observations showed that birds responded to decoys only when within range of sound treatments. Conspecific vocalizations appear to be important proximate cues for seabird colony site selection and should be given priority in management protocols using social attraction. © 2011 The Wildlife Society.     

Natural attenuation of endocrine-disrupting estrogens in an ecologically engineered treatment system (EETS) designed with floating, submerged and emergent macrophytes

Natural attenuation of estrogenic endocrine disrupting compounds (EDCs) such as estriol (E3, natural) and 17α-ethinylestradiol (EE2, synthetic) were evaluated in a designed ecologically engineered treatment system (EETS) along with domestic sewage. These two estrogens are the major contaminants of sewage and found to cause adverse effects on the endocrine system of humans and animals when exposed even in nanogram concentrations. The EETS consisted of three tanks containing diverse biota, viz., aquatic macrophytes, submerged plants, emergent plants, algae and bacteria present in the system mimic the natural cleansing functions of wetlands and help in the treatment of pollutants present in wastewater. During operation, 22 μg/l of E3 and EE2 were separately fed for 10 days each and operated in continuous mode (20 l/day). The floating macrophytes system (Tank 1) was more effective in removing estrogens [E3 - 61.77% (13.59 μg/l); EE2 - 69.09% (15.20 μg/l)] compared to the submerged-emergent macrophytes-based integrated system (Tank 2) [E3 - 16.58% (3.65 μg/l); EE2 - 18.52% (4.08 μg/l)] and submerged-rooted microphytes system (Tank 3) [E3 - 15.20%, (3.35 μg/l); EE2 - 7.72%, (1.70 μg/l)]. On the whole, EETS can effectively treat EDCs [E3 93.56% (20.59 μg/l); EE2 95.34% (20.97 μg/l)]. Removal of COD (68.06%), nitrates (60.02%) and turbidity (83.43%) was also observed simultaneously during EETS operation. The designed EETS is ecologically complex and mechanically simple and has very low energy consumption and function based on a natural cleansing mechanism (attenuation) with esthetic value.     

Development of visual species identification in ducklings: What is the role of imprinting?

The phenomenon of imprinting (a rapid form of exposure learning) is widely presumed to underlie the formation of normal, species-typical social preferences in precocial birds. To determine whether this is in fact the case, 24-h-old domestic and semi-wild mallard ducklings (Anas platyrhynchos) were allowed to follow a stuffed hen of one of three sympatric waterfowl species for 20 min. The models used were mallard, redhead (Aythya americana), and pintail (Anas acuta) hens. When later tested for their preference for the familiar hen in simultaneous choice tests with one of the other two stuffed models, only those birds trained with the Mallard and tested with the Mallard and Pintail models (designated the Mallard versus Pintail group) showed a preference for the familiar model. (That preference was shown by both domestic and semi-wild ducklings.) In none of the other three groups (Mallard versus Redhead, Redhead versus Mallard, and Pintail versus Mallard) was the imprinting procedure effective in producing a preference for the familiar model. When other ducklings were similarly trained with either the Mallard model, a red-and-white-striped box, or a green styrofoam ball, a preference for the familiar model was found in all four groups (Mallard versus Red Box, Red Box versus Mallard, Red Box versus Green Ball, and Green Ball versus Red Box). Increasing the length of the training period from 20 min to 2 h and to 24 h did not produce a preference for the familiar Mallard over the unfamiliar Redhead. These results raise some doubt that imprinting as currently conceived is the behavioural mechanism of visual species identification as it occurs in nature.     

Cholinergic mechanism involved in the nociceptive modulation of dentate gyrus

Acetylcholine (ACh) causes a wide variety of anti-nociceptive effects. The dentate gyrus (DG) region of the hippocampal formation (HF) has been demonstrated to be involved in nociceptive perception. However, the mechanisms underlying this anti-nociceptive role have not yet been elucidated in the cholinergic pain-related neurons of DG. The electrical activities of pain-related neurons of DG were recorded by a glass microelectrode. Two kinds of pain-related neurons were found: pain-excited neurons (PEN) and pain-inhibited neurons (PIN). The experimental protocol involved intra-DG administration of muscarinic cholinergic receptor (mAChR) agonist or antagonist. Intra-DG microinjection of 1 μl of ACh (0.2 μg/μl) or 1 μl of pilocarpine (0.4 μg/μl) decreased the discharge frequency of PEN and prolonged firing latency, but increased the discharge frequency of PIN and shortened PIN inhibitory duration (ID). Intra-DG administration of 1 μl of atropine (1.0 μg/μl) showed exactly the opposite effects. According to the above experimental results, we can presume that cholinergic pain-related neurons in DG are involved in the modulation of the nociceptive response by affecting the discharge of PEN and PIN.