Quantifying visual acuity inHeliconiusbutterflies

Abstract

AbstractHeliconiusbutterflies are well-known for their colourful wing patterns, which advertise distastefulness to potential predators and are used during mate choice. However, the relative importance of different aspects of these signals will depend on the visual abilities ofHeliconiusand their predators. Previous studies have investigated colour sensitivity and neural anatomy, but visual acuity (the ability to perceive detail) has not been studied in these butterflies. Here, we provide the first estimate of visual acuity inHeliconius: from a behavioural optomotor assay, we found that mean visual acuity = 0.49 cycles-per-degree (cpd), with higher acuity in males than females. We also estimated visual acuity from eye morphology and reported slightly lower values (mean visual acuity = 0.38 cpd), but acuity was still higher in males. Finally, we estimated how visual acuity affectsHeliconiusvisual perception compared to a potential avian predator. Whereas the bird predator maintained high resolving power,Heliconiuslost the ability to resolve detail at greater distances, though colours may remain salient. These results will inform future studies ofHeliconiuswing pattern evolution, as well as other aspects in these highly visual butterflies, which have emerged as an important system in studies of adaptation and speciation.