Long-term spatial memory across large spatial scales in Heliconius butterflies.

Locating food in heterogeneous environments is a core survival challenge. The distribution of resources shapes foraging strategies, imposing demands on perception, learning and memory, and associated brain structures. Indeed, selection for foraging efficiency is linked to brain expansion in diverse taxa, from primates to Hymenopterans. Among butterflies, Heliconius have a unique dietary adaptation, actively collecting and feeding on pollen, providing a source of essential amino acids as adults, negating reproductive senescence and facilitating an extended longevity. Several lines of evidence suggest that Heliconius learn the spatial location of pollen resources within an individual's home range, and spatial learning may be more pronounced at these large spatial scales. However, experimental evidence of spatial learning in Heliconius, or any other butterfly, is so far absent. We therefore tested the ability of Heliconius to learn the spatial location of food rewards at three ecologically-relevant spatial scales, representing multiple flowers on a single plant, multiple plants within a locality, and multiple localities. Heliconius were able to learn spatial information at all three scales, consistent with this ability being an important component of their natural foraging behaviour.