Temporal shift in the presence of a chemical cue contributes to a diel shift in sociality

Spatial and temporal variation in animal aggregations may be due to variati on in the presence of cues for aggregation (or disaggregation) or to variat ion in the receptivity of the animal to a particular cue or suite of cues. Spiny lobsters, Panulirus argus, forage solitarily but are often found aggr egated in their diurnal shelters. An important proximate cause of aggregati on among spiny lobsters is a scent they produce that influences shelter cho ice by conspecifics. We examined how variability in the presence of, or res ponse to, such a chemical cue may contribute to diel shifts in sociality am ong spiny lobsters. We conducted a series of Y-maze shelter choice experime nts using lobsters that were either maintained under altered dark:light sch edules in the experimental arena or under natural lighting in the head tank s. Lobsters that were maintained on a light schedule 8 h later than normal chose shelters at their dawn (corresponding to the middle of the night for lobsters in the head tanks); however, their choices of shelter were not inf luenced by scents of conspecifics. Lobsters that were maintained on a sched ule 8 h earlier than normal chose shelters in the middle of their night (co rresponding to dawn for the lobsters in the head tanks). Their choices of s helter were significantly influenced by conspecific scents. These results s uggest that the chemical cues for aggregation, released by spiny lobsters, are present discontinuously, that spiny lobsters are influenced by conspeci fic odours continuously, and that aggregation is controlled by temporal var iation in the presence of a chemical cue. (C) 2000 The Association for the Study of Animal Behaviour.