Alison R. Mercer

An atlas and 3-D reconstruction of the antennal lobes in the worker honey bee, Apis mellifera L. (Hymenoptera : Apidae)

Abstract A model of the 3-dimensional structure of the antennal lobes in the brain of the worker honey bee, Apis mellifera L. (Hymenoptera : Apidae), has been constructed using retrograde cellular marking and computer reconstruction techniques. The model provides a pictorial representation of the spatial organization of structures within the antennal lobe neuropil. In addition, an atlas is provided to aid the identification of invariant morphological landmarks within the antennal lobe, some of which have been described previously. Readily identifiable invariant glomeruli are described in detail, and a hitherto unreported afferent tract of the antennal nerve, the tract “T2-2”, is also identified. Precise descriptions of the arborizations patterns of several deutocerebral interneurones stained intracellularly with cobalt serve to illustrate the advantages of using the atlas and 3-dimensional representations of the antennal lobe represented in this paper.

Changes in brain amine levels associated with the morphological and behavioural development of the worker honeybee

SummaryChanges in biogenic amine levels associated with the morphological and behavioural development of the worker honeybee are examined.A significant increase in amine levels in the head of the honeybee is associated with transition from the larval to pupal stage. Adult emergence is also accompanied by a significant increase in 5-HT levels in the brain, but no significant change in brain dopamine (DA) levels. NADA (N-acetyldopamine) levels increase during larval and pupal development, but in contrast to both DA and 5-HT, drop significantly during the transition from pupa to adult.Levels of DA in the brain of nectar and pollen forager bees, presumed to be among the oldest adults sampled, were found to be significantly higher than in nurses, undertakers or food storers. These results suggest that an age-dependent change in amine levels occurs in the brain of the worker bee. In the optic lobes, levels of DA and 5-HT were found to be significantly higher in pollen forager bees than in all other behavioural groups. Significant differences in amine levels in the optic lobes of nectar foragers and pollen foragers indicate that some differences in amine levels occur independent of worker age. The functional significance of differences in brain amine levels and whether or not biogenic amines play a direct role in the control of honeybee behaviour has yet to be established.

Queen pheromone modulates brain dopamine function in worker honey bees

Honey bee queens produce a sophisticated array of chemical signals (pheromones) that influence both the behavior and physiology of their nest mates. Most striking are the effects of queen mandibular pheromone (QMP), a chemical blend that induces young workers to feed and groom the queen and primes bees to perform colony-related tasks. But how does this pheromone operate at the cellular level? This study reveals that QMP has profound effects on dopamine pathways in the brain, pathways that play a central role in behavioral regulation and motor control. In young worker bees, dopamine levels, levels of dopamine receptor gene expression, and cellular responses to this amine are all affected by QMP. We identify homovanillyl alcohol as a key contributor to these effects and provide evidence linking QMP-induced changes in the brain to changes at a behavioral level. This study offers exciting insights into the mechanisms through which QMP operates and a deeper understanding of the queens ability to regulate the behavior of her offspring.

Morphology and response characteristics of neurones in the deutocerebrum of the brain in the honeybeeApis mellifera

SummaryNeurones restricted to the deutocerebrum of the brain of the honeybee are examined using intracellular recording and staining techniques and are classified according to their morphological characteristics. Three morphological categories of deutocerebral neurones were identified and their physiological properties are investigated.1.A non parametric approach is used to provide a general classification of the responses recorded in this study and to compare the response patterns of deutocerebral neurones belonging to different morphological categories. A more detailed analysis is used to investigate trends within and between populations of deutocerebral neurones grouped according to their morphological characteristics, or according to the type of stimulation applied to the animal.2.None of the cells recorded in this study responded to simple visual stimulation (a light flash). However, many cells responded to one or more of the three forms of antennal stimulation used (a puff of rose scent, a puff of air and a puff of the alarm pheromone isoamylacetate) and certain neurones responded differently to each of these three forms of antennal stimulation. The most common response to all antennal stimuli was an increase in the frequency of action potentials recorded at the onset of the stimulus. Some variation in the response patterns of neurones innervating different regions of the antennal lobe was revealed. However, it was not possible to predict the morphology of deutocerebral neurones based upon their background frequency of action potentials, their response characteristics, or the latency of their responses.

Structural plasticity of identified glomeruli in the antennal lobes of the adult worker honey bee

Adult worker honey bees alter their behaviour with age but retain a strong reliance on sensory information from the antennae. The antennae house a diverse array of receptors, including mechanoreceptors, hygroreceptors, olfactory receptors, and contact chemoreceptors, which relay information to the brain. Antennal sensory neurons that project to the antennal lobes of the brain converge onto second‐order interneurones to form discrete spheres of neuropil, called glomeruli. The spatial organisation of glomeruli in the antennal lobes of the honey bee is constant, but the central distribution of information from receptors tuned to different sensory modalities is unknown.

Analysis of two D1-like dopamine receptors from the honey bee Apis mellifera reveals agonist-independent activity

Dopamine is found in many invertebrate organisms, including insects, however, the mechanisms through which this amine operates remain unclear. We have expressed two dopamine receptors cloned from honey bee (AmDOP1 and AmDOP2) in insect cells (Spodoptera frugiperda), and compared their pharmacology directly using production of cAMP as a functional assay. In each assay, AmDOP1 receptors required lower concentrations of dopamine and 6,7-ADTN for maximal activation than AmDOP2 receptors. Conversely, butaclamol and cis(Z)-flupentixol were more potent at blocking the cAMP response mediated through AmDOP2 than AmDOP1 receptors. Expression of AmDOP1, but not AmDOP2, receptors significantly increased levels of cAMP even in the absence of ligand. This constitutive activity was blocked by cis(Z)-flupentixol. This work provides the first evidence of a constitutively activated dopamine receptor in invertebrates and suggests that although AmDOP1 and AmDOP2 share much less homology than their vertebrate counterparts, they display a number of functional parallels with the mammalian D1-like dopamine receptors.

On the Front Line: Quantitative Virus Dynamics in Honeybee (Apis mellifera L.) Colonies along a New Expansion Front of the Parasite Varroa destructor

Over the past fifty years, annual honeybee (Apis mellifera) colony losses have been steadily increasing worldwide. These losses have occurred in parallel with the global spread of the honeybee parasite Varroa destructor. Indeed, Varroa mite infestations are considered to be a key explanatory factor for the widespread increase in annual honeybee colony mortality. The host-parasite relationship between honeybees and Varroa is complicated by the mites close association with a range of honeybee viral pathogens. The 10-year history of the expanding front of Varroa infestation in New Zealand offered a rare opportunity to assess the dynamic quantitative and qualitative changes in honeybee viral landscapes in response to the arrival, spread and level of Varroa infestation. We studied the impact of de novo infestation of bee colonies by Varroa on the prevalence and titres of seven well-characterised honeybee viruses in both bees and mites, using a large-scale molecular ecology approach. We also examined the effect of the number of years since Varroa arrival on honeybee and mite viral titres. The dynamic shifts in the viral titres of black queen cell virus and Kashmir bee virus mirrored the patterns of change in Varroa infestation rates along the Varroa expansion front. The deformed wing virus (DWV) titres in bees continued to increase with Varroa infestation history, despite dropping infestation rates, which could be linked to increasing DWV titres in the mites. This suggests that the DWV titres in mites, perhaps boosted by virus replication, may be a major factor in maintaining the DWV epidemic after initial establishment. Both positive and negative associations were identified for several pairs of viruses, in response to the arrival of Varroa. These findings provide important new insights into the role of the parasitic mite Varroa destructor in influencing the viral landscape that affects honeybee colonies.

Cannabinoid Receptors Are Absent in Insects

The endocannabinoid system exerts an important neuromodulatory role in mammals. Knockout mice lacking cannabinoid (CB) receptors exhibit significant morbidity. The endocannabinoid system also appears to be phylogenetically ancient—it occurs in mammals, birds, amphibians, fish, sea urchins, leeches, mussels, and even the most primitive animal with a nerve network, the Hydra. The presence of CB receptors, however, has not been examined in terrestrial invertebrates (or any member of the Ecdysozoa). Surprisingly, we found no specific binding of the synthetic CB ligands [3H]CP55,940 and [3H]SR141716A in a panel of insects: Apis mellifera, Drosophila melanogaster, Gerris marginatus, Spodoptera frugiperda, and Zophobas atratus. A lack of functional CB receptors was confirmed by the inability of tetrahydrocannabinol (THC) and HU210 to activate G‐proteins in insect tissues, utilizing a guanosine‐5′‐O‐(3‐[35]thio)‐triphosphate (GTPγS) assay. No orthologs of human CB receptors were located in the Drosophila genome, nor did we find orthologs of fatty acid amide hydrolase. This loss of CB receptors appears to be unique in the field of comparative neurobiology. No other known mammalian neuroreceptor is understood to be missing in insects. We hypothesized that CB receptors were lost in insects because of a dearth of ligands; endogenous CB ligands are metabolites of arachidonic acid, and insects produce little or no arachidonic acid or endocannabinoid ligands, such as anandamide. J. Comp. Neurol. 436:423–429, 2001.

Scaffolding Critical Thinking in the Zone of Proximal Development.

This paper explores student experiences of learning to think critically. Twenty‐six zoology undergraduates took part in the study for three years of their degree at the University of Otago, New Zealand. Vygotsky’s developmental model of the Zone of Proximal Development (ZPD) provided a framework as we examined how critical thinking was developed. There was very little evidence of critical thinking at first year as students experienced a high‐level of material scaffold in the form of course documents, textbooks, problem solving‐exercises and discussions that were primarily aimed at the acquisition of factual knowledge. In large classes students were anonymous to lecturers and they relied on each other for support. In years 2 and 3, learning to do research became the main scaffold for critical thinking and students gradually changed their views about the nature of knowledge. Verbal scaffolding and conversation with lecturers and peers allowed students to extend their ZPD for critical thinking. They began to accept responsibility for their own and their peers’ learning as they practiced being a zoology researcher. These findings are discussed in relation to two approaches to scaffolding in the ZPD and it is suggested that research should be an integral part of the first year if critical thinking remains a key aim for higher education.

An investigation of the role of dopamine in the antennal lobes of the honeybee,Apis mellifera

SummaryThe effects of dopamine applied to the antennal lobes of the honeybee are investigated using the proboscis conditioning paradigm (Kuwabara 1957). The percentage of bees responding to a conditioned olfactory stimulus after a single conditioning trial is reduced significantly by the application of dopamine (10−6M) to the antennal lobes of the bee brain. Reduction in response levels is significantly smaller in bees conditioned to the olfactory stimulus in multiple conditioning trials prior to treatment with dopamine. The effects of dopamine on the percentage of bees responding to a conditioned olfactory stimulus are blocked by the butyrophenone, haloperidol (10−5M). The possible role of dopaminergic interneurones in the antennal lobes of the bee brain is discussed.