The Gut-Brain-Microbiome Axis in Bumble Bees

Abstract

The brain-gut-microbiome axis is an emerging area of study, particularly in vertebrate systems. Existing evidence suggests that gut microbes can influence basic physiological functions and that perturbations to the gut microbiome can have deleterious effects on cognition and lead to neurodevelopmental disorders. While this relationship has been extensively studied in vertebrate systems, little is known about this relationship in insects. We hypothesized that because of its importance in bee health, the gut microbiota influences learning and memory in adult bumble bees. As an initial test of whether there is a brain-gut-microbiome axis in bumble bees, we reared microbe-inoculated and microbe-depleted bees from commercial Bombus impatiens colonies. We then conditioned experimental bees to associate a sucrose reward with a color and tested their ability to learn and remember the rewarding color. We found no difference between microbe-inoculated and microbe-depleted bumble bees in performance during the behavioral assay. While these results suggest that the brain-gut-microbiome axis is not evident in Bombus impatiens, future studies with different invertebrate systems are needed to further investigate this phenomenon.

Keywords: free moving proboscis extension response (FMPER) assays; germ free bees; insect cognition.

Figure 1

(A) The modified tubes used for the behavioral assay. (B) An adult bumble bee during the behavioral assay presented with both colors of paper.

Figure 2

Bumble bee participation in free-moving proboscis extension response (FMPER) assay. No significance between treatments as determined by binomial generalize linear mixed model (GLMM) with maximum likelihood: std. error = 0.4111, z = 0.911, p = 0.362. Error bars indicate 95% confidence intervals.

Figure 3

Bumble bee choice response to the trained color, the novel color, or neither color during the FMPER assay. No significance between treatments as determined by binomial GLMM with maximum likelihood: std. error = 0.4501, z = −0.015, p = 0.988). Error bars indicate 95% confidence intervals.

Figure 4

(A) Kaplan–Meier curve of bumble bee survival probability from experimental round 1 (Kaplan–Meier log-rank test, chi-squared = 4.3, df = 7, p = 0.7) and (B) experimental round 2 (Kaplan–Meier log-rank test, chi-squared = 42.3, df = 9, p < 0.0001) with 95% confidence intervals.