A description and analysis of agonistic behavior patterns in an opisthobranch mollusc, Hermissenda crassicornis.

Abstract

Observation of the encounters which occurred among pairs of Hermissenda crassicornis demonstrated the following: 1. Twenty percent of the encounters are agonistic, involving lunging or biting or both. 2. Agonistic behavior more often follows when the animals meet anterior-to-anterior than when they meet in any other configuration. 3. Initiators of encounters are more likely to win than non-initiators. They are larger than non-initiators and enter encounters head-first more frequently. Knowledge of either the position of the animals or the initiator allows relatively accurate predictions of the eventual winner. Additional knowledge of the size difference does not contribute to improved predictability. 4. The behavior patterns were recorded using I.5 second sampling periods. The sequence of behavior patterns is consistent with a first order Markovian model; this is primarily due to the strong tendency to repeat a pattern just displayed. One can predict the following behavior pattern with an accuracy of 1/3 to 1/4. 5. After removal of the repeated behavior patterns, the transitions between patterns are still consistent with a first order Markovian model. One can now predict the following behavior pattern with an accuracy of 1/5 to 1/6. There exists a greater possibility than before that higher orders of dependency might contribute to the sequence of behavior patterns. 6. The sequence of behavior patterns of agonistic encounters are more rigidly organized than the sequence of non-agonistic encounters. 7. It appears that winners and losers of encounters react in a similar manner to a given behavior pattern of the other.