Abstract
Brain and behavioural lateralization at the population level has been recently hypothesized to have evolved under social selective pressures as a strategy to optimize coordination among asymmetrical individuals. Evidence for this hypothesis have been collected in Hymenoptera: eusocial honey bees showed olfactory lateralization at the population level, whereas solitary mason bees only showed individual-level olfactory lateralization. Here we investigated lateralization of odour detection and learning in the bumble bee, Bombus terrestris L., an annual eusocial species of Hymenoptera. By training bumble bees on the proboscis extension reflex paradigm with only one antenna in use, we provided the very first evidence of asymmetrical performance favouring the right antenna in responding to learned odours in this species. Electroantennographic responses did not reveal significant antennal asymmetries in odour detection, whereas morphological counting of olfactory sensilla showed a predominance in the number of olfactory sensilla trichodea type A in the right antenna. The occurrence of a population level asymmetry in olfactory learning of bumble bee provides new information on the relationship between social behaviour and the evolution of population-level asymmetries in animals.
Highlights
Research on anatomical and functional side-related specializations of the brain has mainly focused on vertebrates [1,2,3]
Bumble bees conditioned to extend their proboscis (PER) revealed better learning performance when trained with their right rather than their left antenna, with a magnitude comparable to that previously found in A. mellifera [11,14]
In honey bees lateralization of olfactory learning is associated with morphological and electrophysiological asymmetries: the number of olfactory sensilla and the electroantennographic responses have been shown to be higher in the right than in the left antenna [11,14,16]
Summary
Research on anatomical and functional side-related specializations of the brain has mainly focused on vertebrates [1,2,3]. Evidence for brain and behavioural lateralization among invertebrates has been reported [4,5,6,7,8,9,10]. When conditioned, using the proboscis extension reflex paradigm (PER) [12], with only one antenna in use, bees showed better learning with their right rather than their left antenna. Evidence for lateralization of olfactory learning in the honey bee has been subsequently confirmed and extended exploiting the same paradigm, using different scents and without any coating of the antennae, i.e. with lateral presentations of odour stimuli [13,14,15,16]. In a large number of teleost fishes the shoaling species appeared to be lateralized at the population level, while the majority of non-shoaling species were lateralized at the individual level [18]
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