You startle me, you don’t

Yellow- and fire-bellied toads (genus Bombina) exhibit textbook examples of a peculiar behavior known as the “unken reflex”, a defense mechanism used to startle predators. When a predator’s attack is perceived as imminent and unavoidable, these dorsally camouflaged toads contract their dorsal muscles, suddenly arch their body, expose their vividly colored ventral side, and release toxins from their skin glands. Documented in many species of amphibians, this behavior is considered a stereotyped, rather invariant, response that serves as a tactic to evade predation.

While surveying populations of the endangered Apennine yellow-bellied toad (Bombina pachypus) in Aspromonte National Park (southern Italy), we found that, even under repeated stimulation (we did our best to mimic a persistent predatory bird) only about half of the local population of toads exhibited this behavior, and that individual toads were highly consistent in their response over multiple trials. In other words, the “unken reflex” seems to be a polymorphic and repeatable trait, rather than a fixed impulse. This unexpected intraspecific variation raises several intriguing questions for future research. What is the origin and adaptive value of this behavioral variation? Does frequency-dependent selection affect the efficacy of startling displays? Could the observed variation in these displays among toads reflect individual personalities?