Learning and Increased Effort Affect Lipid Gene Expression in the Mushroom Bodies of Bombus terrestris; A Possible Model for Flower Handling?

ObjectiveIn this study, we examine the effects of instrumental learning, and increased effort on the gene expression profile in the mushroom bodies of bumblebees (Bombus terrestris). MethodsIn a low-effort group (n=9), Bombus terrestris learned to press a lever to access sugar water solution (instrumental task) and responded with a constant effort for a period of four hours, whereas in a high-effort group (n=10), subjects were trained with the same task, but effort requirement was doubled in the last two hours of the experiment. The gene expression profiles of these two groups were compared with a control group (n=10) where subjects had access to the sucrose solution ad libitum, and no learning or effort manipulation took place. After running the experiment, total RNA from each bumblebees mushroom bodies was shipped to Novogene for high-throughput RNA sequencing (mRNAseq). Gene Ontology (GO) analyses were performed to evaluate the effects of the two training protocols on biochemical pathways. Regression analyses were used to examine the relationship between the top five mRNAs and bumblebee performance on high- and low-effort tasks. ResultsIn total, 150 and 112 genes were deregulated by the low- and high-effort procedures, respectively. Complete hierarchic clustering regarding low- and high-effort groups versus the control was observed. GO analyses of the low- and high effort groups versus control revealed that the deregulated genes were associated with pathways related to lipid metabolism. Analyses of the top five deregulated genes suggested a link between mRNA of LOC100646091 to performance following low effort protocol. ConclusionThe data from the present study showed that exposure to the low- and high-effort reinforcement procedures may be associated with the deregulation of many genes related to lipid metabolism in the bumblebees mushroom bodies. Additionally, data suggest a link between expression of mRNA of LOC100646091 and performance. The procedure used here--learning of an operant task and an increase in the effort required (number of lever presses)--is proposed as a model for bumblebee flower-handling.