Contact with Squid Egg Capsules Increases Agonistic Behavior in Male Squid (Loligo pealei).

Agonistic (aggressive) behavior is costly (I). For this reason. males should tight only when it will increase their reproductive fitness. In some species, the last male to mate with a female before she oviposits sires most of the offspring (2). If Loligo pealei has a similar system of sperm precedence. a male should drive away nearby males when females are about to lay their eggs. In L. pealei. conspecific egg capsules induce other females to lay their eggs (3). Therefore, the presence of egg capsules could pro,· ide male squid with the information that females are about to begin ovipositing. To determine whether male squid might use this information. we tested the effect of squid egg capsules on male agonistic behavior. An earlier report suggested that squid egg capsules may increase male agonistic behavior (4). We also explored which stimuli connected with the egg capsules might influence male behavior. Agonistic behavior in L. pealei is similar to that observed in Lo/igo plei (5). First there is a variety of signaling through skin patterns; then the behavior escalates to Fin Beating. Chasing, (or Fleeing) and finally to Open Arm Charges. In the highly aggressive Open Arm Charge. one squid rushes toward the other squid with his arms in a tight cone. Once he is close to his opponent. he throws open his arms. Sometimes the charging squid contacts and wrestles with the conspecitic. but more often he stops short of the other squid. The effect of egg capsules on male agonistic behavior was tested as follows. Male squid were isolated for 14 to 21 h prior to a trial. Squid were randomly assigned as either the "resident" or "intruder.'' Resident squid were isolated in circular tanks (3 m in diameter. 0.5 m deep). Intruder squid were isolated in rectangular tanks ( 132 X 76 X 43 em). The mantle lengths of the resident and intruder ( 16-21 em) were size-matched to within I em. Water temperature in the tanks was maintained between 14.5°-22.5°C. and the tanks were exposed to an ambient light cycle (June-Aug.). Squid were fed Fundulus spp. on the evening before the trials, which were run early the next day. Each squid was used only once. During a trial, an intruder male was introduced into the circular tank containing the resident. Incidences of Fin Beating, Chases, Open Arm Charges, and other behaviors were recorded. After 20 min (n = 23) or 30 min (n = 10). squid egg mops (16-20 egg capsules attached to an airstone). were placed in the center of the tank for 20 min (n = 16) or 30 min (n = 5) and then removed. One min (median: I min, I st and 3rd quartiles: I min, n = 21) after the addition of an egg mop, squid swam towards it, blew water on it, and finally touched it with their arms. In one set of control trials, airstones were added without egg capsules (Table I). As Table I shows, the presence of egg mops induced a large increase in Open Arm Charges, while the airstone alone had no effect. The increase in Open Arm Charges never occurred prior to physical contact with the egg capsules (49/49 trials). In a further set of experiments, we placed an egg mop under a