Integration of Electrosensory and Mechanosensory Information from the Platypus Bill.

Abstract

A multidisciplinary study of the role of electroreception in the platypus has revealed new details and principles that help us to understand the constraints that operate on feeding under natural conditions. Behavioural studies of a 40 msec reflex head movement to brief electrical stimuli reveal that the whole platypus is much more sensitive to electrical stimuli in the ambient water (50mV/cm threshold) than are individual electroreceptors (2 mV/cm threshold); and that the bill is directional, with an 'electrical axis' that points laterally and downwards, in keeping with the parasagittal alignment of the bands of mucous electroreceptors. Electrophysiological and neuroanatomical studies of the bill representation in S I cortex reveal an elaborate stripe-like organisation, resembling the primate visual cortex, with alternating 0.8 mm bands of combined mechanosensory/electrosensory and mechanosensory processing. As well as providing a map of electric field intensity that could help explain directionality of electroreception, this elaborate organisation could also enable the precise localisation of distant prey by analysing the relation between the activation of push-rod mechanoreceptors sensitive to pressure waves and the instantaneous electroreceptors. While helping to illuminate natural feeding behaviour, our observations are also relevant to conservation issues, such as the limited range of the platypus in the Western drainage that may be understood in terms of the need for higher electrical impedance of ambient water if distant mobile prey are to be successfully detected using electroreception.