Oviposition behaviour is not affected by ultraviolet light in a butterfly with sexually-dimorphic expression of a UV-sensitive opsin

Animal vision is important for mediating multiple complex behaviours. In Heliconius butterflies, vision guides fundamental behaviours such as oviposition, foraging and mate choice. Colour vision in Heliconius involves ultraviolet (UV), blue and long-wavelength sensitive photoreceptors (opsins). Additionally, Heliconius possess a duplicated UV opsin, and its expression varies widely within the genus. In Heliconius erato, opsin expression is sexually dimorphic; only females express both UV-sensitive opsins, enabling UV wavelength discrimination. However, the ecological pressures that have driven these sex-specific differences in visual perception remain unresolved. Heliconius females invest heavily in finding hostplants to lay their eggs, a behaviour heavily reliant on visual cues. We tested whether UV vision is used for oviposition in H. erato and Heliconius himera females by manipulating the availability of UV in behavioural experiments under naturalistic conditions. We found that UV did not influence the number of oviposition attempts or the number of eggs laid. In addition, their hostplant, Passiflora punctata, does not reflect UV wavelengths, and models of H. erato female vision suggest only minimal stimulation of the UV opsins. Overall, these findings suggest that UV wavelengths do not directly affect the ability of Heliconius females to find suitable oviposition sites. Alternatively, UV discrimination could be used in the context of foraging or mate choice, but this remains to be tested.