A Description and Experimental Analysis of a Stereotyped Cheliped Flexion Behaviour in Hermit Crabs

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Abstract
Spontaneous cheliped flexion behaviour of hermit crabs was studied using a large aquarium with a gravel substrate. The effects of chemical, visual and tactile stimuli, as well as intervals between flexions were determined using a smaller tank, which facilitated experimentation. The behaviour consists of bringing the tip of the cheliped to the mouth by flexing the four most distal joints, opening the dactyl, wiping the claw with the third maxillipeds and re-extending. Single flexions are used in feeding to pick-up substrate particles covered with diatoms. The rate of activity increases in the presence of glycine (10-3M) or fish juice. Trains of flexions comprise a cleaning behaviour which is elicited by fouling of the claw with food or petroleum jelly, or by strong concentrations of chemicals (10-1M glycine or sea water of pH9.5). In addition, cleaning flexion behaviour was elicited by a variety of disturbance stimuli, including sudden shadow, reflections from a mirror, vibration, "simulated attack" by a plastic rod, handling, and fighting with conspecific hermit crabs. The implications of this response as a displacement behaviour are discussed. The mean interval between cleaning flexions does not change significantly as glycine concentration is increased from 10-4M to 10-2M, but the mean rate of flexion increases sevenfold and mean adaptation time increases threefold. The mean inter-flexion intervals for the chelipeds of individual animals are not significantly different, but the small cheliped undergoes an average of 1.61 times more flexions than the large one. Spontaneous cheliped flexion behaviour of hermit crabs was studied using a large aquarium with a gravel substrate. The effects of chemical, visual and tactile stimuli, as well as intervals between flexions were determined using a smaller tank, which facilitated experimentation. The behaviour consists of bringing the tip of the cheliped to the mouth by flexing the four most distal joints, opening the dactyl, wiping the claw with the third maxillipeds and re-extending. Single flexions are used in feeding to pick-up substrate particles covered with diatoms. The rate of activity increases in the presence of glycine (10-3M) or fish juice. Trains of flexions comprise a cleaning behaviour which is elicited by fouling of the claw with food or petroleum jelly, or by strong concentrations of chemicals (10-1M glycine or sea water of pH9.5). In addition, cleaning flexion behaviour was elicited by a variety of disturbance stimuli, including sudden shadow, reflections from a mirror, vibration, "simulated attack" by a plastic rod, handling, and fighting with conspecific hermit crabs. The implications of this response as a displacement behaviour are discussed. The mean interval between cleaning flexions does not change significantly as glycine concentration is increased from 10-4M to 10-2M, but the mean rate of flexion increases sevenfold and mean adaptation time increases threefold. The mean inter-flexion intervals for the chelipeds of individual animals are not significantly different, but the small cheliped undergoes an average of 1.61 times more flexions than the large one.