Behavioral and genetic correlates of heterogeneity in learning performance in individual honeybees, Apis mellifera

Learning an olfactory discrimination task leads to heterogeneous results in honeybees with some bees performing very well and others at low rates. Here we investigated this behavioral heterogeneity and asked whether it was associated with particular gene expression patterns in the bee’s brain. Bees were individually conditioned using a sequential conditioning protocol involving several phases of olfactory learning and retention tests. A cumulative score was used to differentiate the tested bees into high and low performers. The rate of CS+ odor learning was found to correlate most strongly with a cumulative performance score extracted from all learning and retention tests. Microarray analysis of gene expression in the mushroom body area of the brains of these bees identified a number of differentially expressed genes between high and low performers. These genes are associated with diverse biological functions, such as neurotransmission, memory formation, cargo trafficking and development

Hinweise anhand Verhaltens- und physiologischen Experimenten

Honeybees have superior abilities to learn and discriminate between enormous number of odors with different carbon chain length and functional group. They learn odors outside the colony during foraging as well as inside the colony while communicating with the hive comrades. Bees can be trained to learn odors in the laboratory in simple and complex forms of learning assays using the popular conditioning paradigm namely, the olfactory conditioning of proboscis extension reflex (PER). I used the same olfactory PER conditioning assay and investigated the influences of different learning and memory related features on the overall performance of bees in complex form of olfactory learning. In addition, I recorded physiological responses from the olfactory neurons in honeybee brain to understand the olfactory coding in presence of the complex background odor used for adaptation. In the first chapter of this dissertation I investigated the role of olfaction in honeybees to detect the presence of pathogenic Varroa mite inside the brood cells. Results showed that bees with higher resistance against the Varroa mitewere able to distinguish between the odors of the healthy and infected brood better than the less resistant bees. This strongly indicated that resistant bees possibly detect the Varroa parasitized brood through recognizing their abnormal odors in the colony. This also indicated that honeybees can possibly learn the odors associated with the Varroa infection in presence of the adapting background odor of the honeybee colony. In the second chapter a cumulative form (complex form) of olfactory conditioning assay was used to train bees to identify and understand the behavioral characteristics of the different types of learning related performer classes present in the population of honeybee. I found that speed of odor learning and odor discriminability were the two most important features that strongly influenced the overall performances of all types of performer classes in honeybee. Furthermore, in the third chapter I used the popular neurophysiological technique of in vivo calcium imaging and investigated the effects of olfactory adaptation on the odor coding of the antennal lobe glomeruli. My results showed that adaptation with the background of complex odor stimuli changed the response strengths and representation patterns of odor in the glomeruli which together confirmed the change in odor coding scheme of the glomerular coding space. These results altogether contributed further to the understanding of neural coding and behavioral learning of odor information in honeybee.Honigbienen besitzen die Fähigkeit eine Vielzahl von Düften anhand von unterschiedlich langen Kohlenstoffketten und unterschiedlichen funktionalen Gruppen zu unterscheiden. Düfte sind für diese Tiere während der Futtersuche und im Stock zur Kommunikation von höchster Wichtigkeit. Bienen lernen Düfte im Labor in unterschiedlich komplexen Lernexperimenten. Hierfür bedient man sich der olfaktorischen Konditionierung des Proboscisstreckungsreflexes (PER). Mit Hilfe solcher Konditionierungsexperimente untersuchte ich die Einflüsse von verschiedenen Lern- und Gedächtniseigenschaften auf die Performance von Bienen in komplexen Formen olfaktorischen Lernens. Zusätzlich habe ich (opto-)physiologische Messungen an olfaktorischen Neuronen im Bienengehirn vorgenommen, um den olfaktorischen Code in Gegenwart von komplexen Hintergrunddüften zu untersuchen. Im ersten Kapitel dieser Dissertation untersuchte ich die Rolle von Olfaktion bei der Aufspürung der pathogenen Milbe Varroa in den Brutzellen von Honigbienen. Die Ergebnisse zeigen, dass Bienen mit einer höheren Resistenz gegen Varroa-Milben besser zwischen den Düften von gesunder und infizierter Brut unterscheiden konnten. Dies deutet stark darauf hin, dass resistente Bienen von Varroa parasitierte Brut durch olfaktorische Merkmale erkennen können. Im zweiten Kapitel wurden die Bienen mit Hilfe einer kumulativen (komplexen) Form der olfaktorischen Konditionierung trainiert um die Ergebnisse der verschiedenen Typen von lernbezogenen Performerklassen interpretieren zu können. Ich fand heraus, dass die Geschwindigkeit des Duftlernens und Duftunterscheidbarkeit die beiden Eigenschaften sind, die die Performance von allen Typen von Performerklassen am meisten beeinflussen. Im letzten Kapitel untersuchte ich unter Anwendung der opto-physiologischen Technik in vivo Calcium Imaging die Effekte von olfaktorischer Adaption auf den Duftcode im Antennallobus. Meine Ergebnisse zeigen, dass Adaption an einen komplexen Hintergrundduft die Antwortstärke erhöht und das glomerulare Aktivitätsmuster von zusätzlich präsentierten Einzeldüften verändert. Diese Ergebnisse tragen dazu bei, die Rolle von Hintergrunddüften in der Umgebung beim neuronalen Coding und das Lernverhalten von Duftinformation in der Honigbiene besser zu verstehen

Odor learning and odor discrimination of bees selected for enhanced hygienic behavior

International audienceAbstractOdor learning and odor discrimination were tested in a line of honeybees selected for increased hygienic behavior (HB) against the Varroa mite and compared with control bees (CB). Olfactory proboscis extension conditioning was used to quantify learning, discrimination, and generalization. Retention tests were performed after 1 h and after 1 day to probe the stability of memory. HB and CB did not differ in their learning, discriminating, generalizing, and remembering behavior when pairs of floral odors and pairs of sting pheromone and floral odor were tested. Colony odor used as a background odor during learning and discrimination reduced the performance in both groups, possibly due to an adaptation effect. This effect was found to be particularly strong in CB. In both groups of test bees, no learning was found if wax caps of Varroa-infected and Varroa-uninfected cells were used as test stimuli, possibly because of the common odors. Volatile odors from Varroa-infected and noninfected pupae, however, were learned and discriminated indicating that the volatile signals are strong enough to override the similar cues of pupae. HB performed somewhat better than CB when infected pupae were used as the rewarded stimulus, but the difference between the two groups of test bees was small. Taken together, we conclude that odor learning and discrimination do not differ between HB and CB as long as general odors are involved, but when specific odor profiles from infected pupae are used as the reinforced signal, then a slightly better performance is seen in HB