Patterns of tail breakage in the ladder snake (Rhinechis scalaris) reflect differential predation pressure according to body size

Abstract

Predator-prey interactions are key factors in the evolution of defensive tactics. In snakes, shy organisms from which direct evidence of predator-prey interactions is difficult to obtain, injuries are potential indicators of both the nature and frequency of interactions. We studied the incidence of tail breakage and body scarring in the ladder snake, Rhinechis scalaris, an actively foraging Mediterranean snake, and tested several hypotheses that link body injuries and snake life-history traits, mainly under sexual and ontogenetic aspects. Evidence is presented supporting an ontogenetic shift in the frequency of tail breakage, with the incidence of tail loss increasing as a logistic function of snake size. We relate this finding to the adaptive significance of ontogenetic shifts in dorsal pattern and the reaction of snakes to approaching predators; small individuals are more likely to remain immobile than are medium to large individuals, the former aided by a concealing dorsal pattern with transverse lines, and the latter by a striped pattern. This species exhibited sex differences in body scarring but not in tail breakage, nor did we encounter evidence to suggest that snakes experience multiple tail breaks over time, thus failing to support the sexual difference and multiple tail breakage hypotheses. Moreover, we failed to find a lower frequency of body scarring than tail breakage; hence, our results do not afford evidence that frequency of tail breakage represents an inefficiency of predators in catching or dispatching ophidian prey.