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Vol. 12 (2005) No. 3 P 188-206




Most of behavioral patterns in animals can be interpreted as passive mechanical reactions to stimuli. This idea of Innate Release Mechanism dominated in ethology for a long time. However, if all types of behavior were caused by this mechanism only, animals would not survive in any novel situation where some new behaviors become necessary. Contrary to the traditional theory, we demonstrate that pill bugs (Armadillidium vulgare, Isopoda, Crustacean) can adapt to a new situation by spontaneously generating a new (special) behavior. In our experiments, each bug was placed to an annulus-shaped substrate surrounded by water (test conditions) or acrylic wall (control conditions). Small obstacles were introduced at regular intervals in the middle of the annulus. Normally, the bugs move in a well-known turn-alternation behavioral pattern, touching the obstacle repeatedly. However, as they are destined to die staying in water for more than about thirty minutes, moving along the water becomes dangerous but crucial for their survival activity, resulting in the emergence of the new type of behavior. Under such conditions, the bugs demonstrated mounting to the obstacles, i.e. the behavior rarely observed in the absence of water. Sometimes, this mounting behavior was observed recurrently after wandering around obstacles without touching the water. In the control experiment, when the annulus substrate was surrounded by acrylic wall, mounting behavior happened rarely. We further study the time series corresponding to the behavioral pattern of touching the obstacles by means of wavelet analysis, in order to reveal characteristic periods of each kind of behavior under different conditions. Several pronounced periods in the interval of 50-200 seconds have been detected in both the experimental and control groups. This result implies that pill bugs scan the environment with certain periods, and express mounting behavior occasionally. In the presence of water, mounting behavior apparently decreases the probability of direct contact with the water. Expression of this kind of adaptive multiple-choice behavior can be interpreted as an “intelligent” activity of pill bugs.

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