Identification of a disturbance signal in larval red-legged frogs, Rana aurora

Animals that are warned about the presence of a predator are more likely to avoid and/or survive an encounter with a predator. Chemical signals releas ed by disturbed or injured conspecifics may provide prey animals with an ea rly warning. In this study we conducted experiments to determine whether la rval red-legged frogs respond to chemical stimuli produced by disturbed con specifics and to examine the chemical compounds that may act as the alarm s ignal. In laboratory tests, groups of tadpoles responded with antipredator behaviours when exposed to chemical cues of disturbed conspecifics but not when exposed to chemical cues of control (undisturbed) conspecifics. In sub sequent tests, disturbed animals increased ammonium (the main metabolic was te of tadpoles) excretion relative to undisturbed individuals. When tadpole s were exposed to low-level ammonium concentrations (1 mg NH4+/litre), they responded by increasing antipredator behaviours. Our results suggest that red-legged frog tadpoles release a chemical that provides conspecifics with an early warning of predator presence, and that ammonium (NH4+) may be a c omponent of the disturbance signal. (C) 1999 The Association for the Study of Animal Behaviour.