The agonistic behavior of lobsters

E. A. Kravitz

Department of Neurobiology, Harvard Medical School,
220 Longwood Avenue, Boston, MA 02115, USA
edward_kravitz@hms.harvard.edu

excerpted from: Serotonin and aggression: insights gained from a lobster model system and speculations on the role of amine neurons in a complex behavior. J Comp Physiol A (2000) 186: 221-238; originally published as a King Solomon Lecture in Neuroethology at the Hebrew University in Jerusalem

While observing fighting behavior among behaviorally naive juvenile lobsters, one cannot help but be struck by the elegance of the unfolding scene. When placed in a new environment, animals pause, then begin to explore the arena, generally keeping close to the walls, which they continually circle. Invariably they meet another animal, and just as invariably, display their principal weapons, the large claws. Mirroring moves, they remain motionless, claws up, standing high on the tips of their walking legs, or they bump, darting to and fro, fore and aft, maintaining the display. The dactyls, the movable fingers of the claws, open wide but do not close to grasp the opponent. Meetings are short, lasting about 30 s, during which, in addition to the display, animals direct streams of urine at each other from the nephropores at the base of their 2nd antennae; then they break off, only to begin exploring again. Few or many meetings may take place, during each of which the display is repeated. If a large size asymmetry exists, the fight ends usually with the smaller animal retreating then refusing to engage the larger in combat. A second component of display may be interposed with the posturing. Here is a ballet, a pas de deux on the ocean floor, in which one animal advances, antennae whipping and claws folded downward, while the other animal retreats, antennae straight up and claws up and open. Then on some unknown cue, the animals completely switch their directions of movement and the use of their appendages. If no decision is reached with either of the displays, one of the animals escalates to the next level of intensity, a move immediately paralleled by the opponent. The transition is stepwise, seamless and irreversible. Now the weapons, the claws, start to be used, but only to grasp the opponent. Like Greco-Roman wrestlers in a giant underwater arena, each combatant tries to overturn the other. If one succeeds, then here too, a decision is made by the retreat of the loser. If not, Fights move to the next, highest level of intensity, a move almost always leading to a decision. Moving with great speed now, animals advance on eachother with claws wide open. Their giant claws snap shut on whatever they can reach, then tail flips, contractions of the large abdominal flexor muscles, move animals back and upwards in attempts to tear their catch from the opponent. The danger of damage is high now, but we seldom see animals losing appendages. Those that do, however, usually will not survive the continued presence of the winner. Losers stop urinating, continually retreat, and tail flip to escape the advance of the winner. The "memory" of losing persists for many days, altering the willingness of animals to engage others in combat. In the wild, fights tend to be short in duration, with decisions made early. Mostly these are decided by the size difference that exists when two random animals meet. Under these circumstances, the making of decisions may not have significant impact on the subsequent willingness to fight, but this remains to be established (references for this paragraph: Scrivener 1971; Atema and Cobb 1980; Huber and Kravitz 1995; Karavanich and Atema 1998a, b; Breithaupt et al. 1999; Rutishauser et al. 1999).

E. A. Kravitz
Department of Neurobiology, Harvard Medical School,
220 Longwood Avenue, Boston, MA 02115, USA
e-mail: edward_kravitz@hms.harvard.edu