Predator mimicry, not conspicuousness, explains the efficacy of butterfly eyespots

Abstract

Large conspicuous eyespots on butterfly wings have been shown to deter predators. This has been traditionally explained by mimicry of vertebrate eyes, but recently the classic eye-mimicry hypothesis has been challenged. It is proposed that the conspicuousness of the eyespot, not mimicry, is what causes aversion due to sensory biases, neophobia or sensory overloads. We conducted an experiment to directly test whether the eye-mimicry or the conspicuousness hypothesis better explain eyespot efficacy. We used great tits (Parus major) as model predator, and tested their reaction towards animated images on a computer display. Birds were tested against images of butterflies without eyespots, with natural-looking eyespots, and manipulated spots with the same contrast but reduced resemblance to an eye, as well as images of predators (owls) with and without eyes. We found that mimetic eyespots were as effective as true eyes of owls and more efficient in eliciting an aversive response than modified, less mimetic but equally contrasting eyespots. We conclude that the eye-mimicry hypothesis explains our results better than the conspicuousness hypothesis and is thus likely to be an important mechanism behind the evolution of butterfly eyespots.

The appearance of mimetic Heliconius butterflies to predators and conspecifics

“…; De Bona et al. ). Also, blue Morpho butterflies show intense iridescent blue coloration on the dorsal side that is involved in males flight patrolling, whereas on the ventral side cryptic colors and big eyespots may have been selected against visual predators (DeVries et al.…”

Colour pattern variation affects predation in chrysomeline larvae

“…For example, experiments involving artificially manipulated prey with variable 'eyespots' suggest that the conspicuousness of the pattern is important in promoting avoidance behaviour in predators (Stevens, Hardman, & Stubbins, 2008). However, other studies (De Bona, Valkonen, L opez-Sepulcre, & Mappes, 2015;Merilaita et al, 2011) support the antipredator function of eyespots regardless of conspicuousness, and the background may influence the deterring function of eyespots .…”

Seasonal plasticity in anti-predatory strategies: Matching of color and color preference for effective crypsis

“…; De Bona et al. ). While defensive mechanisms are often constitutive properties of prey species (e.g., the spines of the hedgehog), they can also be induced by specific environmental conditions predictive of predation risk.…”

“…For example, spidermimicking moths both look and act like their predators to improve their chances of deceiving them (Wang et al 2017). Butterflies bearing large eyespots generally only expose these when threatened to increase their chances of startling predators (Olofsson et al 2012;De Bona et al 2015). While defensive mechanisms are often constitutive properties of prey species (e.g., the spines of the hedgehog), they can also be induced by specific environmental conditions predictive of predation risk.…”