Behavioral Modes Arise From a Random Process in the Nudibranch Melibe.

Stochastic analysis was applied to observations of spontaneous behavior in the carnivorous mollusc Melibe leonina. Six behaviors were denned that could be easily recognized on inspection and it was found that transitions between each of these behaviors could be fully described by a first-order random process without memory of past behavioral choices. The behaviors are organized by frequency of transition into two modes, a feeding mode and a resting mode. Transitions within modes are more likely than transitions between modes, and the feeding and resting modes are linked by a preferred pair of behavioral transitions. The amount of time spent in the feeding mode is positively correlated with body size, but the average length of a feeding episode is independent of size. This suggests that body size regulates the probability of entry into feeding behavior but does not influence the basic pattern of feeding. In the presence of food the animals express nearly continuous feeding behavior, suggesting that food reduces the probability of exiting the feeding mode. This model of spontaneous behavior in Melibe is used to form hypotheses amenable to further exploration through neurophysiological experiments.