FOLLOWING THE INVISIBLE TRAIL - KINEMATIC ANALYSIS OF MATE-TRACKING IN THE COPEPOD TEMORA-LONGICORNIS

We have analysed the fine-scale kinematics of movement of male and fem ale copepods, Temora longicornis, to resolve how these small animals f ind their mates. Location of the trail initially involves rapid random turning and high rates of directional change. Males subsequently incr ease their rate of movement as they follow the trail, and execute a re gular pattern of counter turns in both x,z and y,z planes to stay near or within the central axis of the odour field. Pursuit behaviour of m ales is strongly associated with female swimming behaviour, suggesting that quantifiable variations in the structure of the odour signal rel eased by females affects male tracking. The behavioural components of mate tracking in Temora are very similar to those of other animals tha t employ chemically mediated orientation in their search for mates and food, and we conclude that male Temora find their mates using chemope rception. The kinematic analysis indicates both sequential and simulta neous taxis mechanisms are used by Temora to follow the odour signal. This, in turn, indicates that rather than responding to a diffuse plum e, males are following a signal more accurately characterized as a che mical trail, and copepods appear to use mechanisms that are similar to those employed by trail-following terrestrial insects such as ants. W hile Temora expresses similar behaviours to those of a variety of chem osensory organisms, the ability to track a three-dimensional odour tra il appears unique, and possibly depends on the persistence of fluid-bo rne odour signals created in low Reynolds number hydrodynamic regimes.