The effect of body armature on escape behaviour in cordylid lizards

The possession of armour may affect escape behaviour in two ways. On one hand, by decreasing vulnerability to predators, armour may permit individuals to use habitats and behaviours that are too risky for unarmoured individuals. Alternatively, the possession of armour may have negative trade-offs on other traits involved in antipredator behaviour, such as sprint speed, thus constraining antipredator options relative to those available to unarmoured individuals. To examine these contrasting predictions, we examined species in the lizard family Cordylidae, which contains remarkable morphological diversity, ranging from completely unarmoured to heavily defended species. Moreover, phylogenetic analysis indicates that armour has been an evolutionarily labile trait. We found support for the second prediction. Degree of body armature was inversely correlated with distance run from a predator: heavily armoured species always entered refuges after short distances, whereas many unarmoured lizards continued to flee and could not be induced to enter a refuge. Possession of armour was also negatively related to use of vertical surfaces during escape behavour. These results were unchanged when analysed in a phylogenetic context. Thus, we conclude that the morphological requirements for active flight and armoured defence are incompatible. Heavily armoured species are bulky, have short legs and run more slowly than less armoured species. Rather than constituting an alternative to behavioural antipredator tactics, we conclude that the possession of armour is part of an antipredator syndrome that includes habitat use and behaviour as well as morphology.