Electric Fields Generated by Monotreme Prey Species.

Abstract

The electric sense of the platypus may be used for the detection of prey, as may the similar but less elaborate electrosensory system in the echidna. However, for neither animal has this been shown directly. In this study, further support for the feasibility of an electrosensory role in prey detection was sought by determining whether potential prey items of either animal generate electric fields with appropriate characteristics. Prey items were placed in tap water and recordings made with a pair of electrodes placed near the specimen. Movement-related electric fields of a few to a few hundred µVcm-1 in amplitude were generated by a number of items including shrimps, fish, earthworms, mealworms and cockchafer larvae. Some recorded potentials were at a frequency consistent with an electromyogenic origin, while others were at a lower frequency and seemed more related to the movements of the animal itself than to the underlying muscle activity. No electric fields could be recorded from several other small invertebrate species tested. It is concluded that the platypus would be able to detect some prey items at close range by sensing the electric fields they generate, but this has not been demonstrated for the echidna.