READING THE COPEPOD PERSONAL ADS - INCREASING ENCOUNTER PROBABILITY WITH HYDROMECHANICAL SIGNALS

Females of the calanoid copepod Temora longicornis react to chemical e xudates of male conspecifics with little hops, quite distinct from the ir normal smooth uniform swimming motion. These hops possibly serve to create a hydrodynamical signal in the surrounding water, to increase encounter probability with potential mates. Laser sheet particle image velocimetry was used to investigate the flow fields associated with t hese hops and to compare them to the flow of the feeding current of an adult female. During, and immediately after a hop, the flow field aro und the copepod showed a marked difference from that of a foraging ani mal. During foraging, the highest velocity gradients were located arou nd the feeding appendages of the copepod. During a hop, high velocity gradients are located behind the animal. About 0.5 seconds after the s tart of swimming leg movement, effects of the hop had virtually dissip ated and the flow field resembled that around a foraging animal. The e stimated volume of influence (i.e. the volume around the copepod where the animal has a significant influence on the water) increased about 12-fold during the hop compared with the situation around a foraging a nimal. Furthermore, the rate of viscous energy dissipation within the copepods' volume of influence increased nearly 80-fold. Hops may serve to increase encounter probability, but due to the short duration of t he effect and the high energetic costs they would only be adaptive whe n other cues have indicated that suitable sexual partners are in the v icinity.