Fluid dynamic design of lobster olfactory organs: High speed kinematic analysis of antennule flicking by Panulirus argus

Many organisms use olfactory appendages bearing arrays of microscopic hairs to pick up chemical signals from the surrounding water or air. We report a morphometric and high speed kinematic analysis of the olfactory organs (la teral flagella of the antennules, which bear chemosensory aesthetasc hairs) of the spiny lobster, Panulirus argus. Panulirus argus sample specific loc ations by executing a rapid series of antennule flicks at one position, mov ing the antennule to a different spot and then performing another series of flicks. Odorant delivery to an aesthetasc depends on the water motion near it, which depends on its Reynolds number (Re, proportional to both the dia meter and speed of the hair). High speed video enabled us to resolve that: during a series of flicks, an antennule moves down rapidly (aesthetasc Re = 2) and up more slowly (Re = 0.5), pausing briefly (similar to0.54 s) befor e the next downstroke. The antennules of P. argus operate in a range of Re values and interaesthetasc spacings in which penetration of fluid between t he hairs in an array is especially sensitive to changes in speed. Therefore , when antennules flick 'old' water is flushed out of the aesthetasc array during the leaky downstroke and is not picked up again during the less leak y upstroke, hence the antennules can take discrete samples. Thus, by operat ing in this critical Re range these antennules should be particularly effec tive at sniffing.