The timing of chemical signaling with urine in dominance fights of male lobsters (Homarus americanus)

Chemicals carried in the urine are a rich source of information about the identity, sex, aggressive motivation, and other attributes of an animal. In agonistic interactions, animals should be careful about disclosing such information, since it can be used by receivers to the disadvantage of the sender. By adjusting the timing of urine release, the signaler may still influence the behavior of the receiver to its own benefit. Here we investigate the urine signaling of American lobsters (Homarus americanus), necessary for the maintenance of dominance, using a catheter technique with high temporal resolution. We hypothesize that urine release in lobster fights is not continuous but restricted to moments that may elicit a reaction in the receiver beneficial to the sender. We found that eventual winners signaled more readily in the initial phase of the fight. Eventual losers did not show such initial urination. This suggests that a confident lobster may use urine signals to influence the behavior of its opponent into giving up the fight at an early stage. For both winners and losers, urine release is linked to offensive behavior and increases as the intensity of agonistic behavior increases. The coupling of urine release to offensive behaviors appears to improve both the reliability and efficacy of the chemical signal. Releasing urine under the increasing risk of inflicting injury during the fight provides a handicap that may ensure reliability of the threat signal. Furthermore, the immediate coupling of urine components to offensive behavior may help to consolidate the receiver's memory of the signaler's individual scent and thus facilitate future recognition of the dominant animal.