Olfactory coding in the antennal lobe of the bumble bee Bombus terrestris

Marcel Mertes,Jean-Christophe Sandoz,Julie Carcaud

doi:10.1038/s41598-021-90400-6

Abstract

Sociality is classified as one of the major transitions in evolution, with the largest number of eusocial species found in the insect order Hymenoptera, including the Apini (honey bees) and the Bombini (bumble bees). Bumble bees and honey bees not only differ in their social organization and foraging strategies, but comparative analyses of their genomes demonstrated that bumble bees have a slightly less diverse family of olfactory receptors than honey bees, suggesting that their olfactory abilities have adapted to different social and/or ecological conditions. However, unfortunately, no precise comparison of olfactory coding has been performed so far between honey bees and bumble bees, and little is known about the rules underlying olfactory coding in the bumble bee brain. In this study, we used in vivo calcium imaging to study olfactory coding of a panel of floral odorants in the antennal lobe of the bumble bee Bombus terrestris. Our results show that odorants induce reproducible neuronal activity in the bumble bee antennal lobe. Each odorant evokes a different glomerular activity pattern revealing this molecule’s chemical structure, i.e. its carbon chain length and functional group. In addition, pairwise similarity among odor representations are conserved in bumble bees and honey bees. This study thus suggests that bumble bees, like honey bees, are equipped to respond to odorants according to their chemical features.

Highlights

Sociality is classified as one of the major transitions in evolution, with the largest number of eusocial species found in the insect order Hymenoptera, including the Apini and the Bombini
As previously r eported[33], we found a similar arrangement of sensory tracts in the bumble bee antennal lobe as in the honey bee
Single glomeruli from the confocal images were reconstructed (Fig. 1C) and we found 158 ± 4 glomeruli in the antennal lobe of bumble bees (n = 4 bumble bees), a slightly lower number compared to honey bees (~ 160–166 glomeruli)[15,45,46], which roughly corresponds to the number of olfactory receptors (ORs) genes found in bumble b ees[1]

Summary

Introduction

Sociality is classified as one of the major transitions in evolution, with the largest number of eusocial species found in the insect order Hymenoptera, including the Apini (honey bees) and the Bombini (bumble bees). Given the differences in social organization and foraging strategies existing between bumble bees and honey bees, we might expect important differences in how the two species process olfactory information. Bumble bees possess an expanded repertoire of gustatory receptors (GRs) compared to honey b ees[1], suggesting different priorities in the chemosensory systems of the two insects. Bees’ OR repertoires, with a limited number of ortholog genes These observations suggest that their olfactory abilities have adapted to different social and/or ecological conditions. No precise comparison of olfactory coding has been performed so far between honey bees and bumble bees

Methods

Results

Conclusion