BEHAVIORAL-RESPONSES OF MALLORCAN MIDWIFE TOAD TADPOLES TO NATURAL AND UNNATURAL SNAKE PREDATORS

The activity levels of Mallorcan midwife toad tadpoles, Alytes muleten sis, were compared in two natural torrent pools which differed in thei r use by predatory viperine snakes, Natrix maura. Activity levels were lower in a pool regularly used by snakes than they were in a snake-fr ee pool, but were reduced in both pools when snakes were experimentall y introduced in nylon bags. In the presence of snakes, however, activi ty was more suppressed in the pool that was usually snake-free. Corres ponding reductions in activity were also observed when tadpoles were t reated with chemical cues from Mallorcan N. maura in a gravitational f low-through system. However, tadpoles failed to respond to chemical cu es from other species of amphibian-eating snakes, or even to those fro m N. maura collected from a different population in mainland Spain. As none of the snakes used had previously eaten midwife toads, the respo nses cannot be related to previous diet, and seem to be specific to th ose N. maura from the island of Mallorca. As viperine snakes were prob ably introduced to Mallorca about 2000 years ago, the evolution of ant i-predator behaviour in midwife toad tadpoles must have occurred relat ively recently. (C) 1998 The Association for the Study of Animal Behav iour.