Lab and field estimates of active time of chemical alarm cues of a cyprinid fish and an amphipod crustacean

Summary Predation risk is detected by the presence of cues released passively during a predation event. Refinement of risk assessment could occur if prey have the ability to assess cue age. Here, we test for antipredator behavioural responses to chemical alarm cues of varying ages. Fathead minnows, Pimephales promelas, give an antipredator response to alarm cues derived from conspecifc skin extract that has been aged at 18 ◦ C for 0 (fresh) and 3 h, but not after 6 h. Alarm cues from crushed conspecific Gammarus lacustris (Crustacea: Amphipoda), showed a similar chemical longevity. A field test of minnow alarm cues produced broadly similar results for conspecific fathead minnows and heterospecific responses by northern redbelly dace, Phoxinus eos. Close agreement among all three data sets suggests either a common duration of predation risk or a common molecular basis of chemical cues across aquatic taxa. When we heated skin extract to denature and remove half of the constituent proteins, we inactivated biological activity of alarm cue suggesting that protein is required for skin extract to function as an alarm cue in minnows. Protein degradation may be a means of assessing age and, therefore, ecological relevance of chemical information in behavioural decision-making.