Study

Electroreception in monotremes

Pettigrew, John D.

Journal of Experimental Biology, 1999

Peer-reviewednarrative reviewmixed

What they did

Reviews the anatomy, physiology and behaviour of electroreception in the platypus and the echidna, including receptor distribution across the bill, the organisation of the trigeminal projection, and the proposal that prey are localised by comparing the arrival times of an electrical and a mechanical signal from the same event.

Studied in: Ornithorhynchus anatinus, Tachyglossus aculeatus
Sample size: synthesis of monotreme electroreception research

What they found

The platypus bill carries tens of thousands of receptors in stripes, mixing electroreceptors with mechanoreceptors, and the two modalities project to interleaved regions of cortex. Echidnas have far fewer receptors and a correspondingly reduced capacity.

What it means

The authors' reading, and ours. Where they differ, that difference is the point.

How the authors put it

Monotreme electroreception is a bill-based sense integrated with touch, and the timing difference between electrical and mechanical arrival could in principle give range.

How NatureHQ reads it

The source of the most striking idea in the whole subject, and one that should be labelled as a proposal rather than a finding. A shrimp flicking its tail produces an electrical signal that travels almost instantly and a pressure wave that travels at the speed of sound in water; the gap between them grows with distance, so an animal that can time both has a rangefinder. It is elegant, it is consistent with the anatomy, and it has not been demonstrated behaviourally.

Limitations

A review; the electrical–mechanical timing proposal is a hypothesis supported by anatomy rather than by a behavioural test.
Echidna electroreception is characterised far less thoroughly than the platypus.
Receptor counts vary between sources and between individuals.