Electropharyngeograms of pharyngeal pumping activity in six species of free-living nematodes

Abstract

Analysis of the contraction and relaxation of pharyngeal musculature derives from measurements of electrical currents, termed electropharyngeograms (EPG). EPG were recorded from adults of six species of free-living nematodes, Anatonchus amiciae, Aporcelaimus superbus, Plectus parietinus, Mesorhabditis cranganorensis, Seleborca complexa and Panagrellus redivivus, during exposure to artificial pond water (APW) and to 0.1 mg ml^-1 of the neurotransmitter serotonin for 5, 10 and 15 min. A marked difference was observed in the pharyngeal muscle activity of species with grinders in a three-part pharynx compared with that in species with cylindroid or two-part pharynx without grinders. The EPG results from the non-grinder predator A. amiciae showed no electrical activity in response to either APW or serotonin. There was no electrical activity from the non-grinder predator Aporcelaimus superbus in APW and only occasional electrical activity when it was exposed to serotonin; no stylet activity was observed in this species in any treatment combination. The four grinder species, P. parietinus, M. cranganorensis, S. complexa and P.redivivus, gave consistent EPG results in APW, irrespective of the period of exposure. The time intervals between two consecutive pharyngeal pumps were between 1.0 and 1.5 s for M. cranganorensis, S. complexa and P. redivivus but pharyngeal activity of P. parietinus was much slower with intervals of 4.8-4.9 s between two pumps. The effect of serotonin on these four species was inconsistent. Only P.redivivus showed EPG responses that demonstrated an enhanced rate of pharyngeal pumping; the rate of pumping of this species also increased with increase in exposure period to serotonin.