The appearance of mimetic Heliconius butterflies to predators and conspecifics

Abstract

Adaptive coloration is under conflicting selection pressures: choosing potential mates and warning signalling against visually guided predators. Different elements of the colour signal may therefore be tuned by evolution for different functions. We investigated how mimicry in four pairs of Heliconius co-mimics is potentially seen both from the perspective of butterflies and birds. Visual sensitivities of eight candidate avian predators were predicted through genetic analysis of their opsin genes. Using digital image colour analysis, combined with bird and butterfly visual system models, we explored how predators and conspecifics may visualise mimetic patterns. Ultraviolet vision (UVS) birds are able to discriminate between the yellow and white colours of co-mimics better than violet vision (VS) birds. For Heliconius vision, males and females differ in their ability to discriminate co-mimics. Female vision and red filtering pigments have a significant effect on the perception of the yellow forewing band and the red ventral forewing pattern. A behavioural experiment showed that UV cues are used in mating behaviour; removal of such cues was associated with an increased tendency to approach co-mimics as compared to conspecifics. We have therefore shown that visual signals can act to both reduce the cost of confusion in courtship and maintain the advantages of mimicry.