Stomatopod sniffing: the scaling of chemosensory sensillae and flicking behavior with body size

Many crustaceans detect odors from distant sources (such as conspecifics or prey items) by using chemosensory sensillae (aesthetascs) on their antennu les. The morphology and arrangement of the aesthetascs on the antennule and the movement of the antennule through the surrounding fluid during olfacto ry sampling affect the flow of odorants around the sensillae and thus odora nt access to receptors inside the aesthetascs. We examined fluid flow aroun d the olfactory appendages of the stomatopod Gonodactylus mutatus, a crusta cean with excellent olfactory capabilities, a simple arrangement of aesthet ascs on their antennules, and a 10-fold range in post-metamorphic body size s. Using morphometric and kinematic measurements, we calculated several hyd rodynamic parameters including the aesthetasc Reynolds number (Re), the lea kiness of the setal array, and flow rate through aesthetascs and determined how these descriptors of fluid flow changed as the animals increased in si ze. We found that G. mutatus aesthetascs operate over a range of Re where t he leakiness of the aesthetasc array is very sensitive to changes in antenn ule speed and setal dimension. As a result, the rate of fluid flow through the array of aesthetascs varies by a factor of two during different odor-sa mpling motions of the antennule, anti changes over 200-fold as the animals increase in size. The increases in Re, leakiness, and flow rate as the stom atopods grow suggest that stomatopods alter their odor sampling paradigm as they mature, corresponding to changes in diet, preferred habitat and behav ior. (C) 1999 Elsevier Science B.V. All rights reserved.