SEXUAL DICHROMATISM IN SNAKES - SUPPORT FOR THE FLICKER-FUSION HYPOTHESIS

In a recent review of the distribution and evolution of sexual dichrom atism in the Old World viperid snakes of the genus Vipera, Shine and M adsen proposed that males in sexually dichromatic taxa had evolved bri ght contrasting colour patterns because these function to confuse visu ally guided predators by inducing a ''flicker-fusion'' illusion and th us enhance survival of males that move about rapidly in search of mate s. Here we provide support for the flicker-fusion hypothesis obtained from a capture-recapture study of a colour polymorphic population of t he adder, V. berus, that consists of a sexually dichromatic zigzag col our morph and a monochromatic melanistic colour morph. We used mark - recapture data to estimate and compare annual capture and survival pro babilities of melanistic and zigzag male and female individuals. Our r esults revealed that in any given year zigzag males survived significa ntly better than did melanistic males, whereas melanistic females surv ived better than zigzag females. This is consistent with the flicker-f usion hypothesis and suggests that selection from visually guided pred ators acts on the interaction between colour pattern and behaviour.