Predator cognition and the evolution of deimatic displays

Abstract

Deimatic displays are a unique form of prey defence where prey perform a complex display including any combination of movements, postures and visual, auditory, vibratory and/or olfactory stimuli. There is some evidence supporting the idea that displays deter predators, however, it is unclear why. The evolutionary route via which these complex displays evolve is not well understood. Using a novel experimental paradigm, naïve domestic chicks (Gallus gallus domesticus) were presented with computer-generated moth-like deimatic prey to investigate how deimatic displays may have evolved, factors influencing their success, and when prey should produce them. Prey that flicked their forewings to reveal cryptic hindwings deterred predators (when forewing movement was fast), but predators were deterred even more when the hindwings revealed were conspicuously coloured. These results demonstrate that deimatism could evolve if fast movement evolved first, followed by the evolution of conspicuous colouration. Since deimatic displays are widely considered to startle predators, I tested whether factors known to influence the magnitude of startle responses also influence the efficacy of deimatic displays (specifically, hunger, background noise, and affective state). I did not find any effect of hunger on the responses of predators to deimatic displays. Background noise was found to influence the distance at which predators were positioned during the time interval when they decided to attack prey. Although unaltered by an anxious-like state, predators in a depressive-like state were found to attack deimatic prey much faster than conspecifics in a neutral affective state. Finally, I investigated whether temperature influenced the likelihood that live Peacock butterflies (Aglais io) would perform deimatic displays. They displayed more often and for longer durations at cooler temperatures. Thus, in this thesis I provide the first evidence of a viable evolutionary route to deimatism, and establish the factors likely to influence the efficacy and production of deimatic displays. In doing so, I have increased the understanding of the conditions under which deimatism is likely to evolve.