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
selective pressures responsible for sex-specific differences in opsin
expression and visual perception remain unresolved. Female Heliconius
invest heavily in finding suitable hostplants for oviposition, a behaviour
heavily dependent on visual cues. Here, we tested the hypothesis that UV
vision is important for oviposition in H. erato and Heliconius himera
females by manipulating the availability of UV in behavioural experiments
under natural conditions. Our results indicate that UV does not influence
the number of oviposition attempts or eggs laid, and the hostplant,
Passiflora punctata, does not reflect UV wavelengths. 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.