Physical constraints of chemoreception in foraging copepods

The small-scale spatial and temporal dynamics of phycosphere-sized chemical signals entrained within the feeding current of copepods is quantified here by combining flow visualization techniques with electrochemical technology (IVEC-10). Using the 30-mm electrochemical probe sampling at 50 Hz and the velocity gradients created by two marine copepods, we evaluated how odor deformation improves the potential for remote chemoreception. Our data show that when shear is strong, as found in the feeding current of an omnivore, Pleuromamma xiphias,elongation of the chemical signal is greater than that found for an odor signal entrained in the low-shear feeding current of a carnivore, Euchaeta rimana. Furthermore, within the feeding current of a single species, E. rimana, certain areas provided greater potential for remote chemoreception. These results support the hypotheses that chemical signals are deformed by the feeding current and that the feeding current structure enhances signal detection. The deformation of the odor field within the laminar feeding current provides a leading edge that gives a chemosensitive copepod early warning of an approaching odor source. By sensing the leading edge, a copepod could have a few hundred milliseconds to reorient itself with respect to the odor source. Advance warning improves the probability of successful behavior in response to signal sources such as prey, predators, and mates.