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Biomedical subjects

Lars Chittka

Publications and source records attributed to Lars Chittka.

At least 19 recordsLinked to original sources
PubMed2006

Pollen foraging: learning a complex motor skill by bumblebees (Bombus terrestris).

To investigate how bumblebees (Bombus terrestris) learn the complex motor skills involved in pollen foraging, we observed naïve workers foraging on arrays of nectarless poppy flowers (Papaver rhoeas) in a greenhouse. Foraging skills were quantified by measuring the pollen load collected during each foraging bout and relating this to the number of flowers visited and bout duration on two consecutive days. The pollen standing crop (PSC) in each flower decreased drastically from 0530 to 0900 hours. Therefore, we related foraging performance to the changing levels of pollen available (per flower) and found that collection rate increased over the course of four consecutive foraging bouts (comprising between 277 and 354 individual flower visits), suggesting that learning to forage for pollen represents a substantial time investment for individual foragers. The pollen collection rate and size of pollen loads collected at the start of day 2 were markedly lower than at the end of day 1, suggesting that components of pollen foraging behaviour could be subject to imperfect overnight retention. Our results suggest that learning the necessary motor skills to collect pollen effectively from morphologically simple flowers takes three times as many visits as learning how to handle the most morphologically complex flowers to extract nectar, potentially explaining why bees are more specialised in their choice of pollen flowers.

Animals↗
PubMed2006

Traplining in bumblebees (Bombus impatiens): a foraging strategy's ontogeny and the importance of spatial reference memory in short-range foraging.

To test the relative importance of long-term and working spatial memories in short-range foraging in bumblebees, we compared the performance of two groups of bees. One group foraged in a stable array of six flowers for 40 foraging bouts, thereby enabling it to establish a long-term memory of the array, and adjust its spatial movements accordingly. The other group was faced with an array that changed between (but not within) foraging bouts, and thus had only access to a working memory of the flowers that had been visited. Bees in the stable array started out sampling a variety of routes, but their tendency to visit flowers in a repeatable, stable order ("traplining") increased drastically with experience. These bees used shorter routes and converged on four popular paths. However, these routes were mainly formed through linking pairs of flowers by near-neighbour movements, rather than attempting to minimize overall travel distance. Individuals had variations to a primary sequence, where some bees used a major sequence most often, followed by a minor less used route, and others used two different routes with equal frequency. Even though bees foraging in the spatially randomized array had access to both spatial working memory and scent marks, this manipulation greatly disrupted foraging efficiency, mainly via an increase in revisitation to previously emptied flowers and substantially longer search times. Hence, a stable reference frame greatly improves foraging even for bees in relatively small arrays of flowers.

Animals↗
PubMed2006

Animal cognition: an insect's sense of time?

For Immanuel Kant, time was the very form of the inner sense, the bedrock of our consciousness and also the origin of arithmetic ability. New research on bumblebees has shown that even an invertebrate with a brain the size of a pinhead can actively sense the passage of elapsed time, allowing it to predict when certain salient events will occur in the future.

Animals↗
PubMed2006

Behavioural ecology: bees associate warmth with floral colour.

Floral colour signals are used by pollinators as predictors of nutritional rewards, such as nectar. But as insect pollinators often need to invest energy to maintain their body temperature above the ambient temperature, floral heat might also be perceived as a reward. Here we show that bumblebees (Bombus terrestris) prefer to visit warmer flowers and that they can learn to use colour to predict floral temperature before landing. In what could be a widespread floral adaptation, plants may modulate their temperature to encourage pollinators to visit.

Adaptation, Physiological↗
PubMed2006

Recognition of flowers by pollinators.

The flowers of angiosperm plants present us with a staggering diversity of signal designs, but how did this diversity evolve? Answering this question requires us to understand how pollinators analyze these signals with their visual and olfactory sense organs, and how the sensory systems work together with post-receptor neural wiring to produce a coherent percept of the world around them. Recent research on the dynamics with which bees store, manage and retrieve memories all have fundamental implications for how pollinators choose between flowers, and in turn for floral evolution. New findings regarding how attention, peak-shift phenomena, and speed-accuracy tradeoffs affect pollinator choice between flower species show that analyzing the evolutionary ecology of signal-receiver relationships can substantially benefit from knowledge about the neural mechanisms of visual and olfactory information processing.

Animals↗
PubMed2006

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.

Animal Communication↗
PubMed2006

Do honeybees detect colour targets using serial or parallel visual search?

In humans, visual search tasks are commonly used to address the question of how visual attention is allocated in a specific task and how individuals search for a specific object (;target') among other objects (;distractors') that vary in number and complexity. Here, we apply the methodology of visual search experiments to honeybees, which we trained to choose a coloured disc (target) among a varying number of differently coloured discs (distractors). We measured accuracy and decision time as a function of distractor number and colour. We found that for all colour combinations, decision time increased and accuracy decreased with increasing distractor number, whereas performance increased when more targets were present. These findings are characteristic of a serial search in primates, when stimuli are examined sequentially. We found no evidence for parallel search in bees, which would be characterized by a ;pop out' effect, in which the slope of decision time (and accuracy) over distractor number would be near zero. Additionally, we found that decision time and number of errors were significantly higher when bees had to choose a blue target among yellow distractors compared with the inverse colour combination, a phenomenon known as search asymmetry in humans.

Animals↗
PubMed2005

Social learning: public information in insects.

Although it has received less coverage than in vertebrates, the study of insect social learning has a rich history with spectacular examples of how individuals extract knowledge from other animals. Several new studies on crickets and social bees have now shown how insects can adjust their behaviour adaptively by making use of cues generated inadvertently by other individuals.

Animals↗
PubMed2005

Chemical compounds of the foraging recruitment pheromone in bumblebees.

When the frenzied and irregular food-recruitment dances of bumblebees were first discovered, it was thought that they might represent an evolutionary prototype to the honeybee waggle dance. It later emerged that the primary function of the bumblebee dance was the distribution of an alerting pheromone. Here, we identify the chemical compounds of the bumblebee recruitment pheromone and their behaviour effects. The presence of two monoterpenes and one sesquiterpene (eucalyptol, ocimene and farnesol) in the nest airspace and in the tergal glands increases strongly during foraging. Of these, eucalyptol has the strongest recruitment effect when a bee nest is experimentally exposed to it. Since honeybees use terpenes for marking food sources rather than recruiting foragers inside the nest, this suggests independent evolutionary roots of food recruitment in these two groups of bees.

Animal Feed↗
PubMed2005

Bumblebees, humble pollinators or assiduous invaders? A population comparison of foraging performance in Bombus terrestris.

Worldwide trade in non-native bumblebees remains largely unrestricted despite well-documented cases where introductions of non-native bees have gone dramatically wrong. Within Europe, indiscriminate importation of non-native populations of bumblebees (Bombus terrestris) for the pollination of glasshouse crops continues on a massive scale. However, no risk assessment has been conducted for these introductions, perhaps because B. terrestris is considered a native species, so shipping populations from one region to another has been implicitly assumed to present no risk. This view is clearly unjustified because Bombus terrestris populations differ significantly in their genetic makeup as demonstrated by strong differences in coat colour and behavioural traits. Therefore, for the first time we compare an important competitive trait, namely foraging performance, between commercially available B. terrestris populations in contrasting environments. We test whether commercially reared populations differ in their nectar foraging performance and whether this is influenced by both their source environment and the one they are introduced into. We do this by means of a reciprocal transplant experiment. Strong, consistent inter-population differences in performance occurred irrespective of test location: Canary Island bees (B. t. canariensis) were superior to Sardinian bees (B. t. sassaricus), which were generally superior to mainland European bees (B. t. terrestris). These inter-population differences in performance were largely explained by inter-population variation in forager size, with larger bees being superior foragers. However, even when body size was accounted for, "native" bees were not superior to transplanted non-native bees in all but one case. We conclude that non-native populations, especially those with large foragers, can be highly competitive foragers. This could lead to their establishment and displacement of native bees. Therefore, we recommend that unregulated movements of non-native B. terrestris populations within Europe should not be carried out without a full risk assessment.

Animals↗
PubMed2005

Seeing the light: illumination as a contextual cue to color choice behavior in bumblebees.

The principal challenge faced by any color vision system is to contend with the inherent ambiguity of stimulus information, which represents the interaction between multiple attributes of the world (e.g., object reflectance and illumination). How natural systems deal with this problem is not known, although traditional hypotheses are predicated on the idea that vision represents object reflectance accurately by discounting early in processing the conflating effects of illumination. Here, we test the merits of this general supposition by confronting bumblebees (Bombus terrestris) with a color discrimination task that can be solved only if information about the illuminant is not discounted but maintained in processing and thus available to higher-order learned behavior. We show that bees correctly use the intensity and chromaticity of illumination as a contextual cue to guide them to different target colors. In fact, we trained bees to choose opposite, rather than most similar, target colors after an illumination change. This performance cannot be explained with a simple color-constancy mechanism that discounts illumination. Further tests show that bees do not use a simple assessment of the overhead illumination, but that they assess the spectral relationships between a floral target and its background. These results demonstrate that bees can be color-constant without discounting the illuminant; that, in fact, they can use information about the illuminant itself as a salient source of information.

Animals↗
PubMed2005

Colouration in crab spiders: substrate choice and prey attraction.

Australian crab spiders Thomisus spectabilis ambush pollinating insects, such as honeybees (Apis mellifera) on flowers, and can change their body colour between yellow and white. It is traditionally assumed that the spiders change their colour to match the flower colour, thus rendering them cryptic to insect prey. Here, we test this assumption combining state-of-the-art knowledge of bee vision and behavioural experiments. In the field, yellow spiders are only found on yellow daisies (Chrysanthemum frutescens), whereas white spiders are found on yellow and white daisies. These field patterns were confirmed in the laboratory. When given the choice between white and yellow daisies, yellow spiders preferred yellow daisies, whereas white spiders showed only a slight but non-significant preference for white flowers. Thus, T. spectabilis select background colours according to their own body colour. When viewed from a distance, bees use an achromatic signal produced by their green receptors for target detection. Through this visual channel, white spiders on white flowers, and yellow spiders on yellow flowers are virtually undetectable. From a closer distance of a few centimetres, when bees evaluate colour contrast, the combination of spider colour against different flower backgrounds affected the response of honeybees, but not in ways predicted by a classical crypsis/conspicuousness interpretation. Yellow spiders on yellow flowers are not perfectly matched when interpreted through the colour vision of a honeybee. Nevertheless, honeybees showed indifference to the presence of a spider, equally landing on vacant or spider-occupied flowers. Likewise, white spiders are poorly hidden on white flowers, as white spiders reflect ultraviolet light strongly, while white flowers do not. Surprisingly, bees are attracted to this contrast, and significantly more honeybees preferred white flowers occupied by white spiders. White spiders on yellow flowers produce the highest colour contrast and bees again preferred spider-occupied flowers. Yellow spiders on white flowers were the only pairing where bees rejected spider-occupied flowers, especially in cases where the contrast between the two was relatively strong. Thus, T. spectabilis select flower colours adaptively in a way that deceives honeybees, or at least does not deter them.

Animals↗
PubMed2005

The role of UV in crab spider signals: effects on perception by prey and predators.

Australian crab spiders Thomisus spectabilis sit on the petals of flowers and ambush prey such as honeybees. White-coloured T. spectabilis reflect in the UV (UV+ spiders) and previous research has shown that their presence, curiously, attracts honeybees to daisies. We applied an UV-absorber (Parsol) to create UV-absorbing (UV-) spiders that did not reflect any light below 395 nm wavelength. These physical changes of visual signals generated by crab spiders caused honeybees to avoid flowers with UV- spiders on their petals. They also affected the perception of UV- spiders by honeybees and a potential avian predator (blue tits). Compared to UV+ spiders, UV- spiders produced less excitation of the UV-photoreceptors in honeybees and blue tits, which translated into a reduced UV-receptor contrast and a reduced overall colour contrast between UV- spiders and daisy petals. Our results reveal that a clean physical elimination of reflection in the UV range affects perception in predators and prey and ultimately changes the behaviour of prey.

Animals↗
PubMed2005

Honeybee (Apis mellifera) vision can discriminate between and recognise images of human faces.

Recognising individuals using facial cues is an important ability. There is evidence that the mammalian brain may have specialised neural circuitry for face recognition tasks, although some recent work questions these findings. Thus, to understand if recognising human faces does require species-specific neural processing, it is important to know if non-human animals might be able to solve this difficult spatial task. Honeybees (Apis mellifera) were tested to evaluate whether an animal with no evolutionary history for discriminating between humanoid faces may be able to learn this task. Using differential conditioning, individual bees were trained to visit target face stimuli and to avoid similar distractor stimuli from a standard face recognition test used in human psychology. Performance was evaluated in non-rewarded trials and bees discriminated the target face from a similar distractor with greater than 80% accuracy. When novel distractors were used, bees also demonstrated a high level of choices for the target face, indicating an ability for face recognition. When the stimuli were rotated by 180 degrees there was a large drop in performance, indicating a possible disruption to configural type visual processing.

Animals↗
PubMed2005

Analysis of pollen and nectar of Arbutus unedo as a food source for Bombus terrestris (Hymenoptera: Apidae).

The mineral, total amino acid, and sterol compositions of pollen collected by Apis mellifera L. were compared with the pollen of a plant consumed by Bombus terrestris (L.): Arbutus unedo L. This plant provides the predominant food resource for the main autumn generation of B. terrestris in southern France. Honey bees also forage on this plant, although only for nectar. The mineral composition of 30 pollen samples collected by honey bees is close to the presently known requirements of A. mellifera, except for Cu and Mn, which are substantially lower. The total amino acid mean composition of a set of 54 pollen samples fits the basic requirements of honey bees except for valine, isoleucine, and methionine, which are present in lower concentrations in all the samples. For pollen of A. unedo, the amino acid balance is not very different from that of the survey. The main sterolic component in pollen of A. unedo, beta-sitosterol, is known to have antifeedant effects on A. mellifera. Honey bees cannot dealkylate C29 sterols like beta-sitosterol or delta5-avenasterol to obtain C27 cholesterol and ecdysteroids. Because these phytosterols as well as cholesterol are nearly absent from pollen of A. unedo, the metabolic capabilities of Apis seem unadapted to this plant. On the contrary, pollen of A. unedo is freely consumed by B. terrestris, which develops huge autumn populations solely on this food. These data indicate that the sterolic metabolisms of B. terrestris and A. mellifera differ, allowing separation in foraging activity.

Amino Acids↗
PubMed2004

Bumblebees (Bombus terrestris) sacrifice foraging speed to solve difficult colour discrimination tasks.

The performance of individual bumblebees at colour discrimination tasks was tested in a controlled laboratory environment. Bees were trained to discriminate between rewarded target colours and differently coloured distractors, and then tested in non-rewarded foraging bouts. For the discrimination of large colour distances bees made relatively fast decisions and selected target colours with a high degree of accuracy, but for the discrimination of smaller colour distances the accuracy decreased and the bees response times to find correct flowers significantly increased. For small colour distances there was also significant linear correlations between accuracy and response time for the individual bees. The results show both between task and within task speed-accuracy tradeoffs in bees, which suggests the possibility of a sophisticated and dynamic decision-making process.

Animals↗