Decision-Making and Turn Alternation in Pill Bugs ()

Twelve pill bugs (Armadillidium vulgare, Isopoda, Cmstacean) were examined in 200 successive T-mazes. When obstacles are present, A. vulgare tend to move by means of turn alternation, which is generally considered an innate adaptive behavior. With a decrease in air moisture, the bugs have a tendency to increase their turn alternation rate. However, in such long successive T-mazes as in this study, continued turn alternation should actually accelerate the bugs' desiccation. This fact implies that turn alternation cannot always work adaptively. In this trade-off situation, while three individuals kept turn alternation at a high rate (1) and four at a low rate, (2), the other five spontaneously increased the rate of turn alternation and then decreased it (3). This instability of turn alternation in group (3) is interpreted as resulting not from stochastic factors but rather from the bugs' own decision-making, and seems to be anescape behavior used to get out of the experimental apparatus. In order to verify thedecision-making hypothesis, all animals were subsequently tested in another successive T-maze apparatus, where the ends of the chosen alleys were shut, i.e., with 50 successive blind alleys. In this situation, while individuals of groups (1) and (2) continued to wander inside the apparatus, those of group (3) found a vertical roughwall, climbed it, and escaped from the apparatus in the middle of the experiment. Mostof the unexercised individuals in the control experiment did not show climbingbehavior