Photobehavior as an inducible defense in the marine copepod Calanopia americana

The photoresponses of Calanopia americana involved in diel vertical migration (DVM) were tested after exposure of copepods to the following predator kairomones: (1) crude body mucus from fish (Fundulus heteroclitus), (2) crude body mucus from ctenophores (Mnemiopsis leidyi), and (3),10-kDa F. heteroclitus odor. Crude mucus (10% v/v) from fish and ctenophores and,10-kDa fish odor at several concentrations (0.01–10 % v/v) either shifted or removed the ascent response of C. americana to relative rates of irradiance decrease that occur at sunset. The estimated concentrations of uronic acids and sulfated glycosaminoglycans in the test solutions are consistent with bioactive kairomone molecules being modified amino sugars. The phenotypic plasticity of photoresponses underlying DVM in this marine copepod species indicates that vertical migration in some marine crustacean zooplankton is likely an inducible defense, as reported for crustacean zooplankton from other habitats. An ‘‘inducible defense’ ’ is defined as a phenotypic change in an organism that is caused directly by a cue associated with a biotic agent, and this defense usually decreases the likelihood of future encounters, or the effects of future at-tacks, by this agent (Harvell and Tollrian 1999). This defen