Characterization of an alarm pheromone secreted by amphibian tadpoles that induces behavioral inhibition and suppression of the neuroendocrine stress axis

• Published in: Hormones and behavior Vol. 55; no. 4; pp. 520 - 529
• Main Authors: Fraker, Michael E., Hu, Fang, Cuddapah, Vindhya, McCollum, S. Andy, Relyea, Rick A., Hempel, John, Denver, Robert J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-04-2009; Elsevier; Elsevier BV
• Subjects: Amphibian; Animal behavior; Animal Communication; Animals; Anti-predator behavior; Behavioral psychophysiology; Biochemistry; Biological and medical sciences; Cellular biology; Corticosterone; Corticosterone - metabolism; Cues; Freshwater; Fundamental and applied biological sciences. Psychology; Hormones; Hormones and behavior; Hypothalamo-Hypophyseal System - metabolism; Inhibition (Psychology); Larva - metabolism; Peptides - metabolism; Pheromones - metabolism; Pituitary-Adrenal System - metabolism; Predation; Predation risk assessment; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Ranidae - metabolism; Reptiles & amphibians; Skin - metabolism; Skin secretion; Stress; Tadpole; Time Factors; Anti-predator behavior; Skin secretion; Corticosterone; Predation risk assessment; Tadpole; Amphibian; Stress; Evaluation; Steroid hormone; Secretion; Pheromone; Glucocorticoid; Characterization; Adrenal hormone; Skin; Behavior; Inhibition; Predation risk
• ISSN: 0018-506X; 1095-6867
• DOI: 10.1016/j.yhbeh.2009.01.007

Many species assess predation risk through chemical cues, but the tissue source, chemical nature, and mechanisms of production or action of these cues are often unknown. Amphibian tadpoles show rapid and sustained behavioral inhibition when exposed to chemical cues of predation. Here we show that an alarm pheromone is produced by ranid tadpole skin cells, is released into the medium via an active secretory process upon predator attack, and signals predator presence to conspecifics. The pheromone is composed of two components with distinct biophysical properties that must be combined to elicit the behavioral response. In addition to the behavioral response, exposure to the alarm pheromone caused rapid and strong suppression of the hypothalamo–pituitary–adrenal (HPA) axis, as evidenced by a time and dose-dependent decrease in whole body corticosterone content. Reversing the decline in endogenous corticosterone caused by exposure to the alarm pheromone through addition of corticosterone to the aquarium water (50 nM) partially blocked the anti-predator behavior, suggesting that the suppression of the HPA axis promotes the expression and maintenance of a behaviorally quiescent state. To our knowledge this is the first evidence for aquatic vertebrate prey actively secreting an alarm pheromone in response to predator attack. We also provide a neuroendocrine mechanism by which the behavioral inhibition caused by exposure to the alarm pheromone is maintained until the threat subsides.