COVER-SEEKING BEHAVIOR IN JUVENILE AND ADULT CRAYFISH, ORCONECTES RUSTICUS - EFFECTS OF DARKNESS AND THIGMOTACTIC CUES

The cover-seeking behavior of juvenile and adult crayfish, Orconectes rusticus, was examined in relation to the relative importance of darkn ess and thigmotactic cues. Crayfish (N = 12 per experiment) were obser ved in individual aquaria 5 times per day, with at least 30 min betwee n observations, for a 3-day period. Their positions were recorded as e ither within or outside the provided covert(s). When presented with a choice between a clear thigmotactic cover or open area (Experiment Ia) , adult crayfish were observed in the cover significantly more often. Juvenile crayfish were observed in the open area significantly more of ten, but burrowed into the gravel to provide a measure of darkness (sh adow) and tactile sensation. Experiment Ib presented crayfish with a c hoice between a dark thigmotactic cover and an open area; both adults and juveniles were observed in the cover significantly more than in th e open area. In Experiment II, crayfish were given a simultaneous choi ce;among a clear thigmotactic cover, a dark thigmotactic cover, and op en area. Both age groups were observed in the dark cover more often th an the other 2 conditions and were never observed in the clear cover. Although a clear cover was acceptable to adult crayfish (Experiment Ia ), it was not acceptable to juveniles. Adults appeared to prefer dark cover to clear cover; juveniles altered their environment to provide s hadowed cover, rather than utilize a clear cover. Thus, juveniles also appear to prefer ''darkness'' and will alter their environment accord ingly. In Experiment III, crayfish were given a simultaneous choice am ong: a reduced-thigmotactic dark cover; a clear thigmotactic cover; an d open area. Adults chose the large dark cover significantly more than the open area, but not significantly more than the clear thigmotactic cover. Adults that used the clear thigmotactic cover pulled gravel in to their shelters, thus providing a measure of darkness. Juveniles cho se the large dark cover significantly more than either the clear thigm otactic cover or the open area. Darkness appears to be the controlling factor in cover-seeking of juveniles; adults will modify cover provid ing only thigmotactic cues when dark thigmotactic cover is absent. Dar kness plus thigmotactic cues, however, is the most preferred cover for both age groups.