Effects of chemical cues from two piscine predators, natal predator regime, and time since cue introduction, on the movements of aquatic isopods (Caecidotea communis)

The ability to detect predators at a distance through chemical cues is often essential for prey, but spatial variation in predator presence and species may promote variability in the reactions of prey subpopulations. We collected isopods (Caecidotea communis) from three ponds: two with fish (sunfish in one, shiners in the other), and one without. We exposed individuals from these three subpopulations to kairomones and diet cues released by sunfish (Lepomis spp.) or golden shiners (Notemigonus crysoleucas). We used time-lapse photography to calculate the rate of movement and proportion of time isopods spent moving, both soon after cue introduction and twenty-five minutes later. Thus, we tested for reactions to cues, for rapid cue degradation or short-term habituation, and for effects of natal pond. The isopods from all subpopulations did not alter their rate of movement nor their percent of time moving when exposed to dechlorinated tap water or cues from sunfish. The isopods from the pond containing shiners significantly increased their proportion of time moving, and showed a not significant tendency to move more rapidly, when exposed to cues from shiners as opposed to dechlorinated tap water. Our results are the first to demonstrate that isopods may lack a behavioral response to chemicals indicating likely imminent danger from the same species of fish as occur in their natal pond.