Behavioral responses of sea lamprey (Petromyzon marinus) to a putative alarm cue derived from conspecific and heterospecific sources

The sea lamprey, Petromyzon marinus, exhibits a spectacular alarm response to the odor emitted from decayed conspecifics that may differ substantially in function from the well-characterized system in ostariophysan fishes. Here, we report a series of three laboratory experiments designed to characterize the behavioral responses of migratory-phase lampreys to a set of odors derived from conspecific and heterospecific tissues, determine whether sex or sexual maturation alters these responses, and ascertain if the putative alarm substance derives from a particular region of the body. A number of the findings were consistent with the prevailing predator-avoidance paradigm for fish alarm substances released from the skin after predator attack in that: (1) dilute odors derived from freshly ground skin were highly repellent; (2) the substance is contained in the organism early in life; (3) the odor derived from a close relative was avoided whereas those of a distant relative were not; and (4) upon sexual maturity female response to the alarm substance was attenuated. Two interesting patterns arose that differed substantially from the prevailing paradigm: (1) conspecific odors remained repellent after 96 h of aerobic decay; and (2) the cue was emitted from multiple areas of the body, not just the skin, and the repellency of the odor derived from any tissue increased in accordance with its mass. A persistent cue emitted from several sources suggests a broader ecological function than the detection and avoidance of a predator.