Peripheral eye dimensions in Longwing (Heliconius) butterflies vary with body size and sex but not light environment nor mimicry ring

This study tests if tropical forest butterflies occupying similar light environments converge on eye morphology to meet shared demands of visual sensitivity'.Total corneal surface area and facet diameters were measured and adjusted to body size for four species of Heliconius (Lepidoptera: Nymphalidae) butterflies that belong to two mimicry' rings that frequent different light environments.Total corneal surface area and facet diameter differed among species, but not between mimicry rings and light environment.Heliconius cydno had the largest corneal surface areas, H. erato had the second largest, while H. sapho 2 i\ H. rnelpomened not differ from each other.Heliconius cydno and H. erato had larger facets than H. cydno and H. rnelpomene.Facet diameter was not linked to either mimicry ring or chide.Males had larger corneas relative to body size than females, but facet diameter did not differ by sex.As predicted, facet diameter differed by region of the eye.Lastly, we found that larger eyes had more facets.VMiile the eyes of Heliconius generally seem to be larger than those of similarly sized butterflies, tbe hy'pothesis that light environment affects eye morphology was not supported and the finding that neither mimicry' ring nor phylogeny explains facet diameter is perplexing, but suggests that adaptation to contrasting light environments might be instead found in the physiology of the visual system.