Spatial preferences influence associations between magnitude and space in honeybees

Many animals, including humans, non-human primates, birds, and honeybees, show associations between space and quantity. This 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 of associations between space and quantity are not consistent among species and remain poorly understood, particularly in invertebrates. In the current study, we examine the link between magnitude and space in honeybees to increase our understanding of the evolution of space and quantity associations in diverse taxa. We first tested if free-flying honeybees have an innate left-to-right, or right-to-left bias for associations between quantity and space similar to the mental number line, and/or if they showed any evidence of a vertical preference. Along the horizontal orientation, bees only showed a preference for larger quantities presented on the right, suggesting a left-to-right magnitude bias interacting with a weak right spatial bias. There was no evidence of a vertical magnitude preference due to an overall ventral preference in bees. We next tested if honeybees could be specifically conditioned to order quantities along left-to-right or right-to-left dimensions of quantity and space. Whilst honeybees could learn either a left-to right or right-to-left quantity and space association during conditioning trails, in subsequent unconditioned tests, bees again only demonstrated a significant preference for arranging the
larger quantities on the right when trained to a left-to-right quantity association. Our results
suggest that bees have an interacting innate left-to-right quantity bias and right spatial bias. Our study permits a better understanding of the evolution of quantity processing and the complexities that exist in spatial-magnitude associations.