Background choice and immobility as context dependent tadpole responses to perceived predation risk.

The association of immobility and camouflage is widespread as a defensive mechanism in prey from varied taxa. However, many experiments assessing the reaction of prey to predator cues are conducted under artificial laboratory conditions. In a previous experiment we observed the tadpoles of Ololygon machadoi (Hylidae) to respond to predator visual and/or chemical cues by choosing backgrounds that improve their disruptive properties, but detected no associated reduction of movement. Here we experimentally demonstrate this response in the species' natural habitat, on backgrounds where the tadpoles are likely to achieve their best camouflage. We also tested whether previous experiences could influence both background choice and immobility in O. machadoi tadpoles. These novel experimental results suggest that a defensive behavior-i.e., reduction of movement-in these tadpoles is more strongly expressed under the natural conditions where they evolved, compared to laboratory conditions where prey and predator were brought into closer contact. Besides, previous experiences are likely to play an important role in expressed defensive responses.