The concepts of 'sameness' and 'difference' in an insect

Honeybee Genome Sequencing Consortium. Insights into social insects from the genome of the honeybee Apis mellifera

Here we report the genome sequence of the honeybee Apis mellifera, a key model for social behaviour and essential to global ecology through pollination. Compared with other sequenced insect genomes, the A. mellifera genome has high A+T and CpG contents, lacks major transposon families, evolves more slowly, and is more similar to vertebrates for circadian rhythm, RNA interference and DNA methylation genes, among others. Furthermore, A. mellifera has fewer genes for innate immunity, detoxification enzymes, cuticle-forming proteins and gustatory receptors, more genes for odorant receptors, and novel genes for nectar and pollen utilization, consistent with its ecology and social organization. Compared to Drosophila, genes in early developmental pathways differ in Apis, whereas similarities exist for functions that differ markedly, such as sex determination, brain function and behaviour. Population genetics suggests a novel African origin for the species A. mellifera and insights into whether Africanized bees spread throughout the New World via hybridization or displacement.

Categorization of visual stimuli in the honeybee Apis mellifera

Categorization refers to the classification of perceptual input into defined functional groups. We present and discuss evidence suggesting that stimulus categorization can also be found in an invertebrate, the honeybee Apis mellifera, thus underlining the generality across species of this cognitive process. Honeybees show positive transfer of appropriate responding from a trained to a novel set of visual stimuli. Such a transfer was demonstrated for specific isolated features such as symmetry or orientation, but also for assemblies (layouts) of features. Although transfer from training to novel stimuli can be achieved by stimulus generalization of the training stimuli, most of these transfer tests involved clearly distinguishable stimuli for which generalization would be reduced. Though in most cases specific experimental controls such as stimulus balance and discriminability are still required, it seems appropriate to characterize the performance of honeybees as reflecting categorization. Further experiments should address the issue of which categorization theory accounts better for the visual performances of honeybees.

Interval Timing by an Invertebrate, the Bumble Bee Bombus impatiens

Sensitivity to temporal information and the ability to adjust behavior to the temporal structure of the environment should be phylogenetically widespread. Some timing abilities, such as sensitivity to circadian cycles, appear in a wide range of invertebrate and vertebrate taxa [1,2]. Interval timing--sensitivity to the duration of time intervals--has, however, only been shown to occur in vertebrates [3,4]. Insect pollinators make a variety of decisions that would appear to require the ability to estimate elapsed durations. We exposed bumble bees to conditions in which proboscis extension was reinforced after a fixed duration had elapsed or after either of two fixed durations had elapsed. Two groups of bees were trained with a short duration (either 6 s or 12 s) and a long duration (36 s) in separate experimental phases (independent timing groups), whereas two other groups were trained with a short duration (either 6 s or 12 s) and long duration (36 s) always intermixed unpredictably (multiple timing groups). On long intervals, independent timing groups waited longer than mixed timing groups to generate the first response and responded maximally near the end of the interval. Multiple timing groups waited the same amount of time on average before generating the first response on both long and short intervals. On individual trials, multiple timing groups appeared to time either the long duration only or both the short and long durations: most trials were characterized by a single burst of responding that began between the short and long duration values or by two bursts of responding with the first burst bracketing the short value and the second burst beginning in anticipation of the long value. These results show that bumble bees learn to time interval durations and can flexibly time multiple durations simultaneously. The results indicate no phylogenetic divide between vertebrates and invertebrates in interval timing ability.

Social insects: from selfish genes to self organisation and beyond

Selfish gene and self-organisation approaches have revolutionised the study of social insects and have provided unparalleled insights into the highly sophisticated nature of insect social evolution. Here, we briefly review the core programs and interfaces with communication and recognition studies that characterise these fields today, and offer an interdisciplinary future perspective for the study of social insect evolutionary biology.

Social Learning: Ants and the Meaning of Teaching

Recent research on ants shows that running in tandem might serve the function of teaching naïve ants about the path to a target. Although these new experiments represent perhaps the most highly controlled study of teaching in animals to date, the findings prompt the question of how teaching formally differs from other forms of communication.

Sensory memory for odors is encoded in spontaneous correlated activity between olfactory glomeruli

Sensory memory is a short-lived persistence of a sensory stimulus in the nervous system, such as iconic memory in the visual system. However, little is known about the mechanisms underlying olfactory sensory memory. We have therefore analyzed the effect of odor stimuli on the first odor-processing network in the honeybee brain, the antennal lobe, which corresponds to the vertebrate olfactory bulb. We stained output neurons with a calcium-sensitive dye and measured across-glomerular patterns of spontaneous activity before and after a stimulus. Such a single-odor presentation changed the relative timing of spontaneous activity across glomeruli in accordance with Hebb's theory of learning. Moreover, during the first few minutes after odor presentation, correlations between the spontaneous activity fluctuations suffice to reconstruct the stimulus. As spontaneous activity is ubiquitous in the brain, modifiable fluctuations could provide an ideal substrate for Hebbian reverberations and sensory memory in other neural systems.

Associative visual learning, color discrimination, and chromatic adaptation in the harnessed honeybee Apis mellifera L

We studied associative visual learning in harnessed honeybees trained with monochromatic lights associated with a reward of sucrose solution delivered to the antennae and proboscis, to elicit the proboscis extension reflex (PER). We demonstrated five properties of visual learning under these conditions. First, antennae deprivation significantly increased visual acquisition, suggesting that sensory input from the antennae interferes with visual learning. Second, covering the compound eyes with silver paste significantly decreased visual acquisition, while covering the ocelli did not. Third, there was no significant difference in the visual acquisition between nurse bees, guard bees, and foragers. Fourth, bees conditioned with a 540-nm light stimulus exhibited light-induced PER with a 618-nm, but not with a 439-nm light stimulus. Finally, bees conditioned with a 540-nm light stimulus exhibited PER immediately after the 439-nm light was turned off, suggesting that the bees reacted to an afterimage induced by prior adaptation to the 439-nm light that might be similar to the 540-nm light.

Effects of caffeine on olfactory and visual learning in the honey bee (Apis mellifera)

Although caffeine is known to improve alertness and arousal in humans and other mammals, its impacts on specific behaviours, including complex cognitive processes, remain controversial. We reasoned that the availability of an easily manipulable, but behaviourally complex invertebrate organism with a simpler nervous system would be beneficial to this field of research. We used a popular behavioural model, the honeybee, to evaluate the effects of caffeine on (1) the development of olfactory learning and (2) the performance in complex learning paradigms, including a 'delayed-match-to-sample' task and visual associative learning. To evaluate the efficacy of caffeine treatment, a variety of doses (0.4-400 ng/1 mg of body mass) were applied topically to tethered individuals. Behavioural testing was performed with either tethered or free-flying adult honeybees. We show that caffeine has marked cognitive effects in this species. In young honeybees, it reduces the age at which restrained individuals are able to learn an olfactory associative task, whereas in older, free-flying bees, caffeine improves both motivation and cognitive performance in complex learning tasks. Our results suggest that the honeybee model may be useful in explaining caffeine-related behavioural changes not only in this species, but also in mammalian systems.

Honeybees (Apis mellifera) holding on to memories: response competition causes retroactive interference effects

Five experiments on honeybees examined how the learning of a second task interferes with what was previously learned. Free flying bees were tested for landmark-based memory in variations on a paradigm of retroactive interference. Bees first learned Task 1, were tested on Task 1 (Test 1), then learned Task 2, and were tested again on Task 1 (Test 2). A 60-min delay (waiting in a box) before Test 2 caused no performance decrements. If the two tasks had conflicting response requirements, (e.g., target right of a green landmark in Task 1 and left of a blue landmark in Task 2), then a strong decrement on Test 2 was found (retroactive interference effect). When response competition was minimised during training or testing, however, the decrement on Test 2 was small or nonexistent. The results implicate response competition as a major contributor to the retroactive interference effect. The honeybee seems to hold on to memories; new memories do not wipe out old ones.

Flower choice copying in bumblebees

We tested a hypothesis originating with Darwin that bees outside the nest exhibit social learning in flower choices. Naive bumblebees, Bombus impatiens, were allowed to observe trained bees or artificial bees forage from orange or green flowers. Subsequently, observers of bees on green flowers landed more often on green flowers than non-observing controls or observers of models on orange flowers. These results demonstrate that bumblebees can change flower choice by observations of non-nest mates, a novel form of social learning in insects that could provide unique benefits to the colony.

Further evidence that mice learn a win-shift but not a win-stay contingency under water-escape motivation

Previous research (C. Locurto, C. Emidy, & S. Hannan, 2002) indicated that mice quickly learned a water-escape task under a win-shift contingency but did not exceed chance-level performance under a win-stay contingency. We examined the robustness of this conclusion in two experiments by varying procedural and temporal aspects of that earlier experiment. Results of both experiments indicated that the preference for win-shift learning in mice under water-escape motivation could not be attributed to procedural or design features of that earlier study and were independent of the influence of intertrial interval, normally a variable that produces strong effects on learning. In neither experiment did subjects exposed to a win-stay contingency perform at above-chance levels.

Complex memories in honeybees: can there be more than two?

Foraging honeybees are likely to learn visual and chemical cues associated with many different food sources. Here, we explore how many such sources can be memorized and recalled. Marked bees were trained to visit two (or three) sugar feeders, each placed at a different outdoor location and carrying a different scent. We then tested the ability of the bees to recall these locations and fly to them, when the training scents were blown into the hive, and the scents and food at the feeders were removed. When trained on two feeder locations, each associated with a different scent, the bees could correctly recall the location associated with each scent. However, this ability broke down when the number of scents and feeder locations was increased to three. Performance was partially restored when each of the three training feeders was endowed with an additional cue, namely, a distinct colour. Our results suggest that bees can recall a maximum of two locations when each is associated with a different scent. However, this number can be increased if the scent cues are augmented by visual cues. These findings have implications for the ways in which associations are established and laid down in honeybee memory.

Coevolution of generalist feeding ecologies and gyrencephalic mushroom bodies in insects

Here we demonstrate the independent acquisition of strikingly similar brain architectures across divergent insect taxa and even across phyla under similar adaptive pressures. Convoluted cortical gyri-like structures characterize the mushroom body calyces in the brains of certain species of insects; we have investigated in detail the cellular and ecological correlates of this morphology in the Scarabaeidae (scarab beetles). "Gyrencephalic" mushroom bodies with increased surface area and volume of calycal synaptic neuropils and increased intrinsic neuron number characterize only those species belonging to generalist plant-feeding subfamilies, whereas significantly smaller "lissencephalic" mushroom bodies are found in more specialist dung-feeding scarab beetles. Such changes are not unique to scarabs or herbivores, because the mushroom bodies of predatory beetles display similar morphological disparities in generalists vs. specialists. We also show that gyrencephalic mushroom bodies in generalist scarabs are not associated with an increase in the size of their primary input neuropil, the antennal lobe, or in the number of antennal lobe glomeruli but rather with an apparent increase in the density of calycal microglomeruli and the acquisition of calycal subpartitions. These differences suggest changes in calyx circuitry facilitating the increased demands on processing capability and flexibility imposed by the evolution of a generalist feeding ecology.

Conservation of novel Mahya genes shows the existence of neural functions common between Hymenoptera and Deuterostome

Honeybees have been shown to exhibit cognitive performances that were thought to be specific to some vertebrates. However, the molecular and cellular mechanisms of such cognitive abilities of the bees have not been understood. We have identified a novel gene, Mahya, expressed in the brain of the honeybee, Apis mellifera, and other Hymenoptera. Mahya orthologues are present in Deuterostomes but are absent or highly diverged in nematodes and, intriguingly, in two dipteran insects (fruit fly and mosquito) and Lepidoptera (silk moth). Mahya genes encode novel secretory proteins with a follistatin-like domain (Kazal-type serine/threonine protease inhibitor domain and EF-hand calcium-binding domain), two immunoglobulin domains, and a C-terminal novel domain. Honeybee Mahya is expressed in the mushroom bodies and antennal lobes of the brain. Zebra fish Mahya orthologues are expressed in the olfactory bulb, telencephalon, habenula, optic tectum, and cerebellum of the brain. Mouse Mahya orthologues are expressed in the olfactory bulb, hippocampus, and cerebellum of the brain. These results suggest that Mahya may be involved in learning and memory and in processing of sensory information in Hymenoptera and vertebrates. Furthermore, the limited existence of Mahya in the genomes of Hymenoptera and Deuterostomes supports the hypothesis that the genes typically represented by Mahya were lost or highly diverged during the evolution of the central nervous system of specific Bilaterian branches under the specific selection and subsequent adaptation associated with different ecologies and life histories.

Decisions, decisions: infant language learning when multiple generalizations are possible

Two experiments presented infants with artificial language input in which at least two generalizations were logically possible. The results demonstrate that infants made one of the two generalizations tested, the one that was most statistically consistent with the particular subset of the data they received. The experiments shed light on how learners might go about solving the induction problem for human language.

Invertebrate Memory: Honeybees with a Sense ofDéjà Vu

Recent studies of visual sequence learning in honeybees have investigated the bees' ability to perform delayed-matching-to-sample and their short-term memory during such tasks. The insect's successful performance raises questions about the underlying mechanisms.

Cognitive consonance: complex brain functions in the fruit fly and its relatives

The fruit fly, Drosophila melanogaster, has become a model for the study of a growing number of human characteristics because of the power of its genetics. Higher cognitive functions, however, might be assumed to be out of reach for the little fly. But the cumulative history of cognitive studies in insects and some of their arachnid relatives, as well as specific probing of the capabilities of fruit flies, suggests that even in this ethereal realm these creatures have much to contribute. What are the degrees of sophistication in cognitive behavior displayed by these organisms, how have they been demonstrated, and what is their potential for understanding how our own brains work?

Simultaneous and successive colour discrimination in the honeybee (Apis mellifera)

The colour discrimination of individual free-flying honeybees (Apis mellifera) was tested with simultaneous and successive viewing conditions for a variety of broadband reflectance stimuli. For simultaneous viewing bees used form vision to discriminate patterned target stimuli from homogeneous coloured distractor stimuli, and for successive discrimination bees were required to discriminate between homogeneously coloured stimuli. Bees were significantly better at a simultaneous discrimination task, and we suggest this is explained by the inefficiency with which the bees' brain can code and retrieve colour information from memory when viewing stimuli successively. Using simultaneous viewing conditions bees discriminated between the test stimuli at a level equivalent to 1 just-noticeable-difference for human colour vision. Discrimination of colours by bees with simultaneous viewing conditions exceeded previous estimates of what is possible considering models of photoreceptor noise measured in bees, which suggests spatial and/or temporal summation of colour signals for fine discrimination tasks. The results show that when behavioural experiments are used to collect data about the mechanisms facilitating colour discrimination in animals, it is important to consider the effects of the stimulus viewing conditions on results.

Visual working memory in decision making by honey bees

The robustness and plasticity of working memory were investigated in honey bees by using a delayed matching-to-sample (DMTS) paradigm. The findings are summarized as follows: first, performance in the DMTS task decreases as the duration between the presentation of the sample stimulus and the presentation of the comparison stimuli is increased. This decrease is well approximated by an exponential decay function. Performance is significantly better than random-choice level even at delays as long as 5 sec and is reduced to random-choice levels at an average delay time of 8.68 +/- 0.06 sec. Second, when the DMTS task involves two samples (one relevant, the other irrelevant), bees can be trained to learn to use the relevant sample to perform the task if (i) the relevant sample is always at a fixed position, or (ii) the relevant sample always has the same place in the sequence of presentation (always first or always second). Bees that have learned to use the relevant sample and to ignore the irrelevant sample can generalize this learning, and apply it to novel sets of sample and comparison stimuli that they have never previously encountered. The findings point to a remarkably robust, and yet plastic, working memory in the honey bee.

Weak and strong priming cues in bumblebee contextual learning

Bees have the flexibility to modulate their response to a visual stimulus according to the context in which the visual stimulus is seen. They readily learn that in one context a yellow target, but not a blue one, should be approached to reach sucrose and that in another context blue, but not yellow,leads to sucrose. Here we contrast the bumblebee's ability to use two types of contextual or priming cue in deciding which of two coloured targets to approach. Bumblebees could perform this task well when the pairs of colours to be discriminated were in two different places, so that the cues associated with each place indicated whether the bees should select a blue or a yellow target. In this case the priming cues were presented concurrently with the rewarded stimuli. Priming cues, which occur a little earlier than a rewarded stimulus, seem less powerful in their ability to bias a bee's choice of rewarded stimulus.

We tried with a variety of methods to train bees to use a priming colour to indicate which of two colours should be approached a few seconds later. Our only success with such sequential priming cues was when each pair of rewarded and unrewarded colours could be distinguished by additional spatial cues. Bees were trained to choose a blue-black checkerboard over a yellow-black checkerboard, after viewing a yellow priming cue, and to choose a uniform yellow target over a uniform blue one, after viewing a blue priming cue. They performed this task almost without error. To see whether bees had associated each rewarded stimulus with the relevant sequential priming cue, bees were tested with a choice between the two rewarded stimuli (the yellow target and the blue-black checkerboard). The bees' choice was biased towards the blue-black checkerboard, when the preceding priming cue was yellow, and towards the yellow target, when the priming cue was blue. We suppose that the experiment works because the presence or absence of the checkerboard provides an additional distinguishing spatial cue that can be linked to and reinforce the sequential one. Under natural conditions, as when bees follow routes,there will normally be such a synergy between spatial and sequential cues.

Antennal tactile learning in the honeybee: Effect of nicotinic antagonists on memory dynamics

Restrained worker honeybees (Apis mellifera L.) are able to learn to associate antennal-scanning of a metal plate with a sucrose reinforcement delivered to the mouthparts. Learning occurs reliably in a single association of the two sensory stimuli. The involvement of nicotinic pathways in memory formation and retrieval processes was tested by injecting, into the whole brain through the median ocellus, either mecamylamine (0.6 microg per bee) or alpha-bungarotoxin (2.4 ng per bee). Saline served as a control. Mecamylamine injected 10 min before the retrieval test impairs the retention level tested 3 h and 24 h after single- or multi-trial learning. Retrieval tests performed at various times after the injection show that the blocking effect of mecamylamine lasts about 1 h. The drug has no effect on the reconsolidation or extinction processes. Mecamylamine injected 10 min before conditioning impairs single-trial learning but has no effect on five-trial learning and on the consolidation process. By contrast, alpha-bungarotoxin only impairs the formation of long-term memory (24 h) induced by the five-trial learning and has no effect on medium-term memory (3 h), on single-trial learning or on the retrieval process. Hence, owing to previous data, at least two kinds of nicotinic receptors seem to be involved in honeybee memory, an alpha-bungarotoxin-sensitive and an alpha-bungarotoxin-insensitive receptor. Our results extend to antennal mechanosensory conditioning the role of the cholinergic system that we had previously described for olfactory conditioning in the honeybee. Moreover, we describe here in this insect a pharmacological dissociation between alpha-bungarotoxin sensitive long-term memory and alpha-bungarotoxin insensitive medium-term memory, the last one being affected by mecamylamine.

Floral scents induce recall of navigational and visual memories in honeybees

During foraging flights, honeybees learn visual and chemical cues associated with a food source. We investigated whether learned olfactory cues can trigger visual and navigational memories in honeybees that assist them in navigating back to a known food source. In a series of experiments, marked bees were trained to forage at one or more sugar water feeders, placed at different outdoor locations and carrying different scents or colours. We then tested the ability of these bees to recall the locations (or colours) of these food sites and to fly to them, when the training scents were blown into the hive, and the scents and food at the feeders were removed. The results show that (1) bees, trained to a single-scented feeder at a given location, can be induced to fly to the same location by blowing the scent into the hive; (2)bees, trained to two feeders, each placed at a different location and carrying a different scent, can be induced to fly to either location by blowing the appropriate scent into the hive; and (3) bees, trained to two feeders, each decorated with a different colour and carrying a different scent, can be induced to find a feeder of either colour by blowing the appropriate scent into the hive. Thus, familiar scents can trigger navigational and visual memories in experienced bees. Our findings suggest that the odour and taste of the nectar samples that are distributed by successful foragers on returning to the hive, may trigger recall of navigational memories associated with the food site in experienced recruits and, thus, facilitate their navigation back to the site.

Drifting bumble bee (Hymenoptera: Apidae) workers in commercial greenhouses may be social parasites

Commercial greenhouses require high densities of managed bumble bee (Bombus occidentalis Greene, 1858 and Bombus impatiens Cresson, 1863) colonies to pollinate crops such as tomatoes (Lycopersicon esculentum Miller). We examined drifting, a behavioural consequence of introducing closely aggregated colonies into greenhouse habitats, to determine possible explanations for observed drifting frequencies. Bee drift is normally associated with increased individual mortality and disease transfer between colonies. In this study, individual bees frequently drifted into and remained within foreign colonies. More drifting bees were found in colonies with higher worker and brood populations and greater pollen stores. Increased intracolony aggressive interactions were not associated with a higher number of drifting bees. Drifting bees had a significantly greater number of mature eggs in their ovaries than did resident worker bees residing in colonies hosting drifters, suggesting that drifting could potentially increase the fitness of individual worker bees and may not be solely a function of disorientation and (or) nectar robbing. Taken together, our results suggest that drifting of workers into foreign colonies within greenhouses may demonstrate a predisposition to social parasitism. This selfish worker reproduction challenges our previous understanding of social insect societies as being cooperative societies.

Grouping of visual objects by honeybees

Recent work has revealed that monkeys as well as pigeons are able to categorise complex visual objects. We show here that the ability to group similar, natural, visual images together extends to an invertebrate - the honeybee. Bees can be trained to distinguish between different types of naturally occurring scenes in a rather general way, and to group them into four distinct categories: landscapes, plant stems and two different kinds of flowers. They exhibit the same response to novel visual objects that differ greatly in their individual, low-level features, but belong to one of the four categories. We exclude the possibility that they might be using single,low-level features as a cue to categorise these natural visual images and suggest that the categorisation is based on a combination of low-level features and configurational cues.

Degree of representation of the matching concept in pigeons (Columba livia)

In Experiment 1, 12 pigeons (Columba livia) were trained on a simultaneous matching-to-sample task with 2 stimuli and then tested with 2 novel stimuli. Half of the birds were trained with a fixed ratio schedule requirement of 1 (FR1) or 20 (FR20) pecks on the sample stimulus. None of the birds showed any evidence of concept-mediated transfer. In Experiment 2, 12 pigeons were trained with 3 stimuli and then tested with the same novel stimuli used in Experiment 1. Half of the birds in each group were trained with either an FR1 or FR20 requirement on the sample stimulus. Two of the FR20 birds showed high levels of transfer to the novel stimuli similar to that of monkeys in a previous study.

Route learning by insects

Ants and other insects often follow fixed routes from their nest to a foraging site. The shape of an ant's route is set, initially, by navigational strategies, such as path integration and the ant's innate responses to landmarks, which depend minimally on memory. With increasing experience, these early routes are stabilised through the learning of views of landmarks and of associated actions. The substitution of memory-based strategies makes an insect's route more robust and precise. The ability to select between different learnt routes might incur additional memory requirements to those needed for performing a route, and lead to the associative grouping of those memories that relate to a particular route.

The binding and recall of snapshot memories in wood ants (Formica rufa L.)

Insects can locate spatial goals by means of 2-D retinotopic views of the surrounding landmarks, which they memorise from the vantage point of the goal. Wood ants acquire such snapshot memories while fixating conspicuous landmarks with frontal retina, and their snapshots extend horizontally at least 120°into the periphery. Are spatially separate items within such an extended snapshot bound together so that a snapshot is recalled as a whole, or are its components recognised individually?

We approached this question by training ants to find food midway between two upright black cylinders of different sizes and then examined where they searched when they were given two cylinders of the same size. If the ants know which cylinder replaces the small cylinder and which the large, they should search at a position where the two equal-sized cylinders subtend the same angles as do the training cylinders when viewed from the feeder. Ants conformed to this prediction under one condition, searching at a shorter distance from the substitute for the large cylinder than from the substitute for the small cylinder. But, under another condition, ants were unable to distinguish between the two equal-sized cylinders. Ants failed when white curtains completely surrounded the platform on which the cylinders were placed. They succeeded when one side of the platform had a patterned curtain.

We suggest that ants take two snapshots at the feeding site, one when facing the small cylinder and one when facing the large cylinder, and that each snapshot includes the patterned curtain, if it is there. Ants will view the patterned curtain with the lateral retina of one eye when facing the small cylinder and with the lateral retina of the other eye when facing the large cylinder. Our data suggest that there may be associative links between these spatially separate components of the snapshot, which cause the memory of the small cylinder or the large cylinder to be recalled according to which eye sees the curtain. It seems that an extended snapshot not only enhances the accuracy of localisation but can also increase the reliability of snapshot recall, provided that the components of a snapshot are bound together.

Orientation and drifting behaviour of bumblebees (Hymenoptera: Apidae) in commercial tomato greenhouses

A novel environment lacking in directional cues may present orientation challenges to foraging bees. We examined orientation and drifting behaviour of Bombus occidentalis Greene and Bombus impatiens Cresson, the two major bumblebee pollinators of greenhouse tomatoes in British Columbia. Our objectives were to establish the extent and frequency of bee drift into foreign colonies and to examine the potential of nest entrance patterns and landmarks to reduce drift in commercial greenhouses. On average, 28% of marked bumblebees drifted into foreign hives, making up 0.3%–34.8% of the population in those colonies. Bees drifted towards the top position when hives were vertically stacked. The use of simple black and white patterns and large landmarks did not affect the number of drifting bees, suggesting that disorientation is not a major contributor to drift or to the substantial loss of adult bees from colonies during their first week in a greenhouse. Bees had decreased foraging times when landmarks were present in the greenhouse and showed a marginally but not significantly increased rate of pollen input to colonies. These studies contribute to understanding bumblebee behaviour in a novel environment and determining whether orientation cues are feasible management options to reduce drift and potential bee loss.

Categorization of Above and Below Spatial Relations by Tufted Capuchin Monkeys (Cebus apella)

Using a matching-to-sample procedure, the researchers investigated tufted capuchins' (Cebus apella) ability to form categorical representations of above and below spatial relations. In Experiment 1, 5 capuchins correctly matched bar-dot stimuli on the basis of the relative above and below location of their constituent elements. The monkeys showed a positive transfer of performance both when the bar-dot distance in the two comparison stimuli differed from that of the sample and when the actual location of the matching stimulus and the nonmatching stimulus on the apparatus was modified. In Experiment 2, the researchers systematically changed the shapes of the located object (the dot) or the reference object (the horizontal bar). These manipulations did not affect the monkeys' performance. Overall, the data suggest that capuchins can form abstract, conceptual-like representations for above and below spatial relations.

Biological significance of distinguishing between similar colours in spectrally variable illumination: bumblebees (Bombus terrestris) as a case study

Individual bumblebees were trained to choose between rewarded target flowers and non-rewarded distractor flowers in a controlled illumination laboratory. Bees learnt to discriminate similar colours, but with smaller colour distances the frequency of errors increased. This indicates that pollen transfer might occur between flowers with similar colours, even if these colours are distinguishable. The effect of similar colours on reducing foraging accuracy of bees is evident for colour distances high above discrimination threshold, which explains previous field observations showing that bees do not exhibit complete flower constancy unless flower colour between species is distinct. Bees tested in spectrally different illumination conditions experienced a significant decrease in their ability to discriminate between similar colours. The extent to which this happens differs in different areas of colour space, which is consistent with a von Kries-type model of colour constancy. We find that it would be beneficial for plant species to have highly distinctive colour signals to overcome limitations on the bees performance in reliably judging differences between similar colours. An exception to this finding was flowers that varied in shape, in which case bees used this cue to compensate for inaccuracies of colour vision.

Cognitive neuroethology: dissecting non-elemental learning in a honeybee brain

The brain of a honeybee contains only 960,000 neurons and its volume represents only 1 mm3. However, it supports impressive behavioral capabilities. Honeybees are equipped with sophisticated sensory systems and have well developed learning and memory capacities, whose essential mechanisms do not differ drastically from those of vertebrates. Here, I focus on non-elemental forms of learning by honeybees. I show that bees exhibit learning abilities that have been traditionally ascribed to a restricted portion of vertebrates, as they go beyond simple stimulus-stimulus or response-stimulus associations. To relate these abilities to neural structures and functioning in the bee brain we focus on the antennal lobes and the mushroom bodies. We conclude that there is a fair chance to understand complex behavior in bees, and to identify the potential neural substrates underlying such behavior by adopting a cognitive neuroethological approach. In such an approach, behavioral and neurobiological studies are combined to understand the rules and mechanisms of plastic behavior in a natural context.

Identification of individual neurons reflecting short- and long-term visual memory in an arthropodo

Ideally, learning-related changes should be investigated while they occur in vivo, but physical accessibility and stability limit intracellular studies. Experiments with insects and crabs demonstrate their remarkable capacity to learn and memorize visual features. However, the location and physiology of individual neurons underlying these processes is unknown. A recently developed crab preparation allows stable intracellular recordings from the optic ganglia to be performed in the intact animal during learning. In the crab Chasmagnathus, a visual danger stimulus (VDS) elicits animal escape, which declines after a few stimulus presentations. The long-lasting retention of this decrement is mediated by an association between contextual cues of the training site and the VDS, therefore, called context-signal memory (CSM). CSM is achieved only by spaced training. Massed training, on the contrary, produces a decline of the escape response that is short lasting and, because it is context independent, is called signal memory (SM). Here, we show that movement detector neurons (MDNs) from the lobula (third optic ganglion) of the crab modify their response to the VDS during visual learning. These modifications strikingly correlate with the rate of acquisition and with the duration of retention of both CSM and SM. Long-term CSM is detectable from the response of the neuron 1 d after training. In contrast to MDNs, identified neurons from the medulla (second optic ganglion) show no changes. Our results indicate that visual memory in the crab, and possibly other arthropods, including insects, is accounted for by functional changes occurring in neurons originating in the optic lobes.

Gorilla ( Gorilla gorilla gorilla) and orangutan ( Pongo abelii) understanding of first- and second-order relations

Four orangutans and one gorilla matched images in a delayed matching-to-sample (DMTS) task based on the relationship between items depicted in those images, thus demonstrating understanding of both first- and second-order relations. Subjects matched items on the basis of identity, color, or shape (first-order relations, experiment 1) or same shape, same color between items (second-order relations, experiment 2). Four of the five subjects performed above chance on the second-order relations DMTS task within the first block of five sessions. High levels of performance on this task did not result from reliance on perceptual feature matching and thus indicate the capability for abstract relational concepts in two species of great ape.

Mice (Mus musculus) learn a win-shift but not a win-stay contingency under water escape motivation

Twenty mice (Mus musculus), the second filial generation offspring from a C57BL/6 and DBA/2J cross, received spatial win-shift and win-stay water escape training within a mixed design in which all mice received both types of training. Acquisition under win-shift was superior to win-stay with respect to errorless trials and latencies regardless of the order in which the procedures were experienced. Win-stay responding did not exceed chance levels during any training phase. These data contradict the claim that win-stay training is the more easily acquired of the 2 acquisition strategies under aversive motivation.

Searching for the memory trace in a mini-brain, the honeybee

To determine general or species-specific properties in neural systems, it is necessary to use comparative data in evaluating experimental findings. Presented here are data on associative learning and memory formation in honeybees, emphasizing a comparative approach. We focus on four aspects: (1) the role of an identified neuron, VUM(mx1), as a neural substrate of appetitive reinforcement; (2) the sequences of molecular events as they correlate with five forms of memory stages; (3) the localization of the memory traces following appetitive olfactory learning; and (4) the brief description of several forms of complex learning in bees (configuration in olfactory conditioning, categorization in visual feature learning, delayed matching-to-sample learning, and latent learning in navigation). VUM(mx1) activity following the conditioned stimulus odor is sufficient to replace the unconditioned stimulus, and VUM(mx1) changes its response properties during learning similarly to what is known from dopamine neurons in the basal ganglia of the mammalian brain. The transition from short- to mid- and long-term forms of memory can be related to specific activation of second messenger cascades (involving NOS, PKA, PKC, and PKM) resembling general features of neural plasticity at the cellular level. The particular time course of the various memory traces may be adapted to the behavioral context in which they are used; here, the foraging cycle of the bee. Memory traces for even such a simple form of learning as olfactory conditioning are multiple and distributed, involving first- and second-order sensory neuropils (antennal lobe and mushroom bodies), but with distinctly different properties. The wealth of complex forms of learning in the context of foraging indicates basic cognitive capacities based on rule extraction and context-dependent learning. It is believed that bees might be a useful model for studying cognitive faculties at a middle level of complexity.

Cognitive architecture of a mini-brain: the honeybee

Honeybees have small brains, but their behavioural repertoire is impressive. In this article we focus on the extent to which adaptive behaviour in honeybees exceeds elementary forms of learning. We use the concept of modularity of cognitive functions to characterize levels of complexity in the honeybee brain. We show that behavioural complexity in the honeybee cannot be explained by independent functions of vertically arranged, domain-specific processing modules, but requires horizontal integration in a central state, and we identify neural mechanisms that may underlie domain-specific processing and central integration. The honeybee may serve as a useful model for the study of intermediate levels of complexity in cognitive functions and the search for their neural substrates.