Sexual dichromatism in snakes: support for the flicker-fusion hypothesis

Abstract

In a recent review of the distribution and evolution of sexual dichromatism in the Old World viperid snakes of the genus Vipera, Shine and Madsen proposed that males in sexually dichromatic taxa had evolved bright contrasting colour patterns because these function to confuse visually guided predators by inducing a "flicker-fusion" illusion and thus enhance survival of males that move about rapidly in search of mates. Here we provide support for the flicker-fusion hypothesis obtained from a capture – recapture study of a colour polymorphic population of the adder, V. berus, that consists of a sexually dichromatic zigzag colour morph and a monochromatic melanistic colour morph. We used mark – recapture data to estimate and compare annual capture and survival probabilities of melanistic and zigzag male and female individuals. Our results revealed that in any given year zigzag males survived significantly better than did melanistic males, whereas melanistic females survived better than zigzag females. This is consistent with the flicker-fusion hypothesis and suggests that selection from visually guided predators acts on the interaction between colour pattern and behaviour.