Survival benefit to antipredator behavior in the amphipod Gammarus minus (Crustacea : Amphipoda) in response to injury-released chemical cues from conspecifics and heterospecifics

A wide range of aquatic taxa use environmental chemical cues for the assess ment of predation risk. We examined whether Gammarus minus (Crustacea: Amph ipoda) exhibit antipredator behavior in response to injury-released chemica ls from conspecifics or heterospecifics (Crustacea: Isopoda). We then exami ned whether behavioral responses to these cues conferred survival benefits to the amphipods. In the first part of this study, we tested the behavioral response of G. minus to the following treatments: I. water containing inju ry-released cues of conspecifics; 2. water containing injury-released cues of a sympatric isopod crustacean, Lirceus fontinalis; or 3. water containin g no cues (control). Relative to the control, Gammarus responded to the con specific cue by moving to the substratum and decreasing activity. In contra st, Gammarus responded to the heterospecific cue by moving up into the wate r column and increasing activity. In the second part of this study, we test ed if the behavioral response to these cues confers a survival benefit to G ammarus when exposed to a predator. A green sunfish (Lepomis cyanellus,) wa s retained behind a partition in the test tanks. Two minutes after the intr oduction of the chemical cues in the first test, the barrier was lifted and predation events recorded. Relative to the control, the time to the first attack increased for Gammarus exposed to conspecific cues and decreased for those exposed to heterospecific cues. These data indicate that Gammarus di stinguish between chemical cues from conspecific and heterospecific crustac eans, and that the antipredator response to conspecific cues confers a fitn ess benefit (i.e. increased survival due to increased time to the first att ack).