Alterations in habituation of the tail flip response in epigean and troglobitic crayfish

We demonstrate that the probability of the crayfish, P. clarkii, to tail fl ip in response to a touch on the dorsal tail fan is dependent on both the s ize and the behavioral state of the animal. Alterations in the animal's int ernal physical state, such as when the animal autotomizes its chelipeds, wi ll cause larger-sized animals to tail flip:; if they were not autotomized, then no tail flip response would occur. Altering the external environment b y removal of water causes small crayfish, which normally habituate slowly t o rapidly habituate. Observation of large adult crayfish in a species, O. a ustralis packardi, one that evolved to live in total cave darkness, reveale d that they are more likely to tail flip than are tile sighted, adult P. cl arkii. Results indicate that the behavioral state of the crayfish can resul t in rapid and long-term alterations in the tail flip response and in habit uation rates to repetitive stimuli. This ability to show plasticity in gain setting may be regulated by neuromodulators and can occur in large adults of the sighted crayfish. Differences between the two species indicate that size may not be the sole contributing factor to account for tail flip behav iors. (C) 2001 Wiley-Liss, Inc.