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Biomedical subjects

Mandyam V Srinivasan

Publications and source records attributed to Mandyam V Srinivasan.

18 recordsLinked to original sources
PubMed2006

The morphology, physiology and function of suboesophageal neck motor neurons in the honeybee.

We report some of the neural and muscular circuitry that allows honeybees to control head movements. We studied neck motor neurons with cell bodies in the suboesophageal ganglion, axons in the first cervical nerve (IK1) and terminals in neck muscles 44 and 51 (muscle classification: Snodgrass in Smithsonian Misc Coll 103:1-120, 1942). We show that muscle 44 actually comprises five separate bundles of muscle fibres (subunits), while muscle 51 is split into two subunits. Eight motor neurons innervate muscles 44 and 51. Two motor neurons have cell bodies in the ventral-median cell body group (one innervates a subunit in muscle 44, the other a subunit in muscle 51). One motor neuron has a ventrally located contralateral cell body (innervating a subunit in muscle 44) and five have laterally located ipsilateral cell bodies. Of the five lateral cells, one innervates a subunit in muscle 51, three selectively innervate subunits in muscle 44 and one co-innervates a subunit in muscle 44 with the contralateral cell. Extracellular recordings revealed three types of visually driven, direction-selective cell-types in each IK1 tuned for leftward, rightward and downward motion over the eyes. The spatiotemporal tuning of the units is similar to that of other visual interneurons in the bee brain.

Action Potentials↗
PubMed2006

Lateralization of olfaction in the honeybee Apis mellifera.

Lateralization of function is a well-known phenomenon in humans. The two hemispheres of the human brain are functionally specialized such that certain cognitive skills, such as language or musical ability, conspecific recognition, and even emotional responses, are mediated by one hemisphere more than the other [1, 2]. Studies over the past 30 years suggest that lateralization occurs in other vertebrate species as well [3-11]. In general, lateralization is observed in different sensory modalities in humans as well as vertebrates, and there are interesting parallels (reviewed in [12]). However, little is known about functional asymmetry in invertebrates [13, 14] and there is only one investigation in insects [15]. Here we show, for the first time, that the honeybee Apis mellifera displays a clear laterality in responding to learned odors. By training honeybees on two different versions of the well-known proboscis extension reflex (PER) paradigm [16, 17], we demonstrate that bees respond to odors better when they are trained through their right antenna. To our knowledge, this is the first demonstration of asymmetrical learning performance in an insect.

Animals↗
PubMed2006

Visual regulation of ground speed and headwind compensation in freely flying honey bees (Apis mellifera L.).

There is now increasing evidence that honey bees regulate their ground speed in flight by holding constant the speed at which the image of the environment moves across the eye (optic flow). We have investigated the extent to which ground speed is affected by headwinds. Honey bees were trained to enter a tunnel to forage at a sucrose feeder placed at its far end. Ground speeds in the tunnel were recorded while systematically varying the visual texture of the tunnel, and the strength of headwinds experienced by the flying bees. We found that in a flight tunnel bees used visual cues to maintain their ground speed, and adjusted their air speed to maintain a constant rate of optic flow, even against headwinds which were, at their strongest, 50% of a bee's maximum recorded forward velocity. Manipulation of the visual texture revealed that headwind is compensated almost fully even when the optic flow cues are very sparse and subtle, demonstrating the robustness of this visual flight control system. We discuss these findings in the context of field observations of flying bees.

Air Movements↗
PubMed2005

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.

Animals↗
PubMed2005

Maturation of odor representation in the honeybee antennal lobe.

The antennal lobe (AL) is the first center for processing odors in the insect brain, as is the olfactory bulb (OB) in vertebrates. Both the AL and the OB have a characteristic glomerular structure; odors sensed by olfactory receptor neurons are represented by patterns of glomerular activity. Little is known about when and how an odor begins to be perceived in a developing brain. We address this question by using calcium imaging to monitor odor-evoked neural activity in the ALs of bees of different ages. We find that odor-evoked neural activity already occurs in the ALs of bees as young as 1 or 2 days. In young bees, the responses to odors are relatively weak and restricted to a small number of glomeruli. However, different odors already evoke responses in different combinations of glomeruli. In mature bees, the responses are stronger and are evident in more glomeruli, but continue to have distinct odor-dependent signatures. Our findings indicate that the specific glomerular patterns for odors are conserved during the development, and that odor representations are fully developed in the AL during the first 2 weeks following emergence.

Acyclic Monoterpenes↗
PubMed2005

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.

Animals↗
PubMed2005

Methyl parathion modifies foraging behaviour in honeybees (Apis mellifera).

We examined the effects of sublethal doses of an organophosphorus insecticide, Methyl Parathion (MeP), on the foraging behaviour of honeybees (Apis mellifera ligustica) in a flight cage. The results revealed that MeP modified the frequency of visits to a feeding station to which the bees had previously been trained. A dose of 50 ng per animal elicited an increase in the frequency of visits to the feeder, compared to control animals. A dose of 10 ng, on the other hand, led initially to a decrease in the visit frequency, followed by an increase to a level above that of the controls. A hypothesis is presented to account for the way in which MeP affects foraging behaviour. We propose that the behavioural assay presented here could be useful as a preliminary screening test to study sublethal effects of pesticides on foraging performance in honeybees.

Animals↗
PubMed2005

Visual control of flight speed in honeybees.

Visual control of flight speed in honeybees (Apis mellifera L.) was investigated by training them to fly through a specially constructed tunnel in which the motion, contrast and texture of the patterns lining the walls could be varied. Manipulation of pattern motion revealed that the speed of flight is controlled by regulating the image motion that is experienced by the eyes. Flight speed is surprisingly robust to changes in the contrast and/or spatial texture of the visual environment, suggesting that the underlying movement-detecting mechanisms estimate the speed of image motion in the eye largely independently of these parameters. This ensures that flight speed depends primarily on the distances to nearby surfaces and not upon their particular visual properties, such as contrast or visual texture. The removal of image motion cues drastically compromises the regulation of flight speed, underscoring their role in this function.

Animals↗
PubMed2005

Interactions of visual odometry and landmark guidance during food search in honeybees.

How do honeybees use visual odometry and goal-defining landmarks to guide food search? In one experiment, bees were trained to forage in an optic-flow-rich tunnel with a landmark positioned directly above the feeder. Subsequent food-search tests indicated that bees searched much more accurately when both odometric and landmark cues were available than when only odometry was available. When the two cue sources were set in conflict, by shifting the position of the landmark in the tunnel during test, bees overwhelmingly used landmark cues rather than odometry. In another experiment, odometric cues were removed by training and testing in axially striped tunnels. The data show that bees did not weight landmarks as highly as when odometric cues were available, tending to search in the vicinity of the landmark for shorter periods. A third experiment, in which bees were trained with odometry but without a landmark, showed that a novel landmark placed anywhere in the tunnel during testing prevented bees from searching beyond the landmark location. Two further experiments, involving training bees to relatively longer distances with a goal-defining landmark, produced similar results to the initial experiment. One caveat was that, with the removal of the familiar landmark, bees tended to overshoot the training location, relative to the case where bees were trained without a landmark. Taken together, the results suggest that bees assign appropriate significance to odometric and landmark cues in a more flexible and dynamic way than previously envisaged.

Analysis of Variance↗
PubMed2004

Olfaction: scent-triggered navigation in honeybees.

The honeybee, Apis mellifera, navigates rapidly and accurately to food sources that are often kilometres away. They achieve this by learning visual cues, such as the location and colour of nectar-bearing flowers, and chemical cues, such as the scent and the taste of the nectar. Here we train bees to visit differently scented sugar feeders placed at specific outdoor locations and find that they can be induced to visit the same locations simply by having the corresponding scent blown into the hive, even when the destinations no longer have the food or carry the scent. A familiar nectar scent can trigger specific memories of a route and therefore expedite navigation to the food source.

Animals↗
PubMed2004

Visual motor computations in insects.

With their relatively simple nervous systems and purpose-designed behaviors and reflexes, insects are an excellent organism in which to investigate how visual information is acquired and processed to guide locomotion and navigation. Flies maintain a straight course and monitor their motion through the environment by sensing the patterns of optic flow induced in the eyes. Bees negotiate narrow gaps by balancing the speeds of the images in their two eyes, and they control flight speed by holding constant the average image velocity as seen with their two eyes. Bees achieve a smooth landing on a horizontal surface by holding the image velocity of the surface constant during approach, thus ensuring that flight speed is automatically close to zero at touchdown. Foraging bees estimate the distance that they have traveled to reach a food source by integrating the optic flow experienced en route; this integration gives them a visually driven "odometer." Insects have also evolved sophisticated visuomotor mechanisms for pursuing prey or mates and possibly for concealing their own motion while shadowing objects of interest.

Animals↗
PubMed2004

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.

Animals↗
PubMed2004

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.

Analysis of Variance↗
PubMed2003

Global perception in small brains: topological pattern recognition in honey bees.

A series of experiments with honey bees demonstrate that their small brains nevertheless possess the ability for topological perception. Bees rapidly learned to discriminate patterns that are topologically different, and they generalized the learned cue to other novel patterns. By contrast, discrimination of topologically equivalent patterns was learned much more slowly and not as well. Thus, although the global nature of topological properties makes their computation difficult, topology may be a fundamental component of the vocabulary by which visual systems represent and characterize objects.

Animals↗
PubMed2003

Honeybee navigation: properties of the visually driven 'odometer'.

Recent work has revealed that honeybees determine distance flown by gauging the extent to which the image of the environment moves in the eye as they fly toward their destination. Here we examine the properties of this visually driven 'odometer', by training bees to fly to a feeder in a tunnel lined with a range of different visual patterns, and analysing their dances when they return to the hive. We find that the odometric signal is relatively unaffected by variations in the contrast and spatial frequency content of the patterns. Furthermore, a strong signal is generated even when the walls or the floor of the tunnel provide only weak optic-flow cues. Thus, distance flown is measured by a visually driven odometer that is surprisingly robust to variations in the texture or sparseness of the visual environment through which the bee flies.

Animals↗