Mechanisms for turn alternation in the tunnelling mud crab helice crassa

Abstract

Turn alternation, or the tendency to turn in the opposite direction to a preceding forced turn, was investigated experimentally in tunnelling mud crabs near their natural habitat. Although crabs alternated significantly following a forced turn of 45°,90°, or 135°, there were no significantdifferences between these conditions. When required to negotiate sequentially three 90° forced turns in one direction followed by a fourth in the opposite direction, the crabs subsequently alternated the last turn, thereby turning in the same direction as the earlier three. The results of the two experiments confirmed a suggestion that, unlike many other invertebrates, mud crabs alternate tactile rather than proprioceptive stimuli when in experiments faced with vertical surfaces. In such situations their thigmotactic behaviour appears to dominate any influence of response-generated proprioceptive cues. © 1990 Taylor & Francis Group, LLC.