Control of information flow through the influence of mechanical and chemical signals during agonistic encounters by the crayfish, Orconectes rusticus

Animals use sensory information when making decisions regarding social status. In particular, crayfish use chemical and possibly mechanical signals to communicate past social history and status. These signals originate in the urine that is actively released during agonistic encounters. We examined the transfer of social information via chemical and mechanical signals by using (1) neutrally buoyant particles, along with a projected light sheet to visualize flow generation, (2) a fluorescent dye to observe urine release and (3) a unique combination of the two techniques to quantify the roles of urine and current generation during agonistic bouts. Both dominant and subordinate crayfish generated currents and appeared to use them to send and sample signals, but dominant crayfish generated more frequent currents than subordinates. Alterations in currents and behaviours suggest that currents are used to transfer social information. Dominant animals released urine during an encounter more frequently than subordinates, and usually did so while engaged with an opponent. In addition, when urine was released, it was transported within these self-generated currents. However, urine was not released every time a current was generated, making urine release relatively rare compared to current generation. A correlation of urine releases with current generation and agonistic behaviours appears to be an indicator for eventual dominant-subordinate relationships. Dominant crayfish showed agonistic behaviours more often when releasing urine. Consequently, chemical signalling influenced a fight opponent's behaviour. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.