Shock or jump: deimatic behaviour is repeatable and polymorphic in the Apennine yellow-bellied toad, Bombina pachypus

Inter-individual variation in antipredatory behaviour has long attracted curiosity among scientists. Deimatism is a complex, multi-component antipredatory strategy consisting of prey suddenly unleashing unexpected defences to startle predators and stop their attack. Deimatic species provide an appealing system to investigate the trade-offs between alternative behavioural phenotypes when faced with a threat. Yet, inter-individual variation in deimatic behaviour is almost unexplored. Here, we simulated a predator attack on 71 yellow-bellied toads, Bombina pachypus, to investigate the extent and pattern of inter-individual variation in the unken reflex behaviour, a deimatic display performed by some amphibians. Results show that deimatic displays consistently differ among B. pachypus individuals. Only about half of the individuals reacted to the simulated predation stimuli by exhibiting the display, which varied in responsiveness, duration and intensity. All the behavioural descriptors were highly repeatable. Finally, we found significant correlations between the measured parameters, defining two prevalent behavioural profiles: individuals quickly doing the unken reflex, with high intensity and long duration of the display, and individuals avoiding the unken reflex but instead escaping. This dichotomy resembles the proactive and reactive patterns in coping styles, and raises intriguing questions on the evolutionary processes shaping multiple adaptive responses to predation within populations.