Spatial preferences influence associations between magnitude and space in honey bees

Many animals, including humans, nonhuman primates, birds and honey bees, show associations between space and quantity. This association can manifest as a left-to-right mental number line (MNL), which is the preference to spatially order smaller quantities on the left and larger quantities on the right. However, the nature and mechanisms underlying this association between space and quantity are inconsistent among species, and they remain poorly understood, particularly in invertebrates. In this study, the link between magnitude and space in honey bees, Apis mellifera, was investigated to improve our understanding of the evolution of space and quantity associations in diverse taxa. First, we tested whether free-flying honey bees have an innate left-to-right or right-to-left bias for associations between quantity and space similar to the MNL and whether bees showed any evidence of a vertical preference. Along the horizontal orientation, bees only showed a preference for larger quantities on the right, indicating a left-to-right magnitude bias interacting with a weak right spatial bias. No evidence of a vertical magnitude preference was observed as bees had an overall ventral preference. Whether honey bees could be conditioned to order quantities along the left-to-right or right-to-left dimensions of quantity and space was also determined. Although honey bees could learn either a left-to-right or right-to-left quantity and space association during conditioning trials, in subsequent unconditioned tests, they only demonstrated a significant preference for arranging larger quantities on the right when trained to a left-to-right quantity association. Results indicate that bees have an innate left-to-right quantity bias interacting with a right spatial bias. The results of this study improve our understanding of the evolution of quantity processing and the complexities that exist in spatial–magnitude associations.