SIZE-DEPENDENT AND SCALE-DEPENDENT CHEMICAL ATTRACTION CONTRIBUTE TO AN ONTOGENIC SHIFT IN SOCIALITY

Caribbean spiny lobsters, Panulirus argru, reside solitarily during th e first months postsettlement, but shift to gregarious shelter use in later juvenile stages, at sizes as small as 15 mm in carapace length. To determine whether receptivity to or production of a chemical attrac tant among spiny lobster conspecifics is dependent upon body size or s patial scale, we conducted a series of overnight Y-maze shelter choice experiments. We placed a test lobster in an experimental arena and al lowed it to choose between two shelters, which differed only in that w ater flowing by one shelter contained sea water that had passed throug h a header tank containing a conspecific. We varied the size of the lo bster in the arena, the size and number of lobsters in the header tank , and the size of the experimental arena. Lobsters of all sizes tested released odours that attracted conspecifics; however, a single small lobster could attract other conspecifics only in the small arena. Lobs ters greater than 15 mm in carapace length were attracted to shelters from which conspecific odours were emanating, while smaller lobsters w ere not. The results of this study suggest that: (1) the earliest bent hic stages (less than 15 mm in carapace length) are unresponsive to co nspecific odours, but lobsters greater than 15 mm in carapace length a re attracted by conspecific odours; and (2) large lobsters produce a s ufficient quantity of scent to attract conspecifics over distances of at least a few metres, whereas small lobsters (15-30 mm in carapace le ngth) cannot. Body size- and spatial scale-dependent attraction could contribute to the shift from solitary to gregarious shelter use among Caribbean spiny lobsters. (C) 1998 The Association for the Study of An imal Behaviour.