Electroreception (Wayne's 6th Sense)

Hello everyone,
Wayne has beaten me at posting about electroreception, but since my group's chosen BIOL1040 eConference assignment topic was electroreception differences between the Guiana dolphin and the Atlantic stingray, I thought I could provide some interesting information.

Wayne correctly summarises the origin of electroreception in fish: the lateral line. While I'm not sure what the lateral line has diversified into in the mammalian vertebrate lineage, the electroreception of monotremes and the Guiana dolphin arises from mechanosensory organs (and, interestingly, a different set of nerves). These same mechanosensory organs (whiskers, to us mortals) are widely used in marine mammal architectures (e.g. seals). The paper on the Guiana dolphin even suggested that the mechanosensory organs of other mammals may have branched into electroreceptive roles in other mammals, too.

Electroreception is quite an interesting phenomenon in itself: as far as I can tell, electroreception in mammals occurs directly via potentials across the nerve cells of the electroreception organs, usually with the assistance of a gel-like substance. Platypodes even have structural mechanisms that are thought to reduce noise ('daisy chains'). Fishies have far more structurally complex organs, but I'm not sure exactly how their sense works: it appears to be caused by a cell membrane potential gradient (as in mammals) but there are still 'kinocillia' in some electrosensory organs—perhaps movement of a kinocillium assists in detection?

Another interesting point is the fact that humans don't have mechanosensory whiskers. Is this because the nerve-blood vessel assemblies do not exist in humans, or do our lips (and 'fake' whiskers) occupy the same region? I have often heard that the lips are very sensitive to both pressure and temperature gradients. Would it be possible to biologically engineer electrosenses in humans? This brings up yet another interesting genetic biology question: how did electroreceptors evolve from mechanoreceptors? Did the nerve endings just become more exposed, until they could detect electric fields readily? This suggests that other animals could very easily have (limited) electroreceptive abilities, at least in water. Perhaps our lips can detect large electric field gradients, also?

I shall have to provide the paper references later, when I have more time. A search for 'Guiana dolphin electroreception' should reveal the paper on the Guiana dolphin, and a search for 'Euryhaline stingray electroreception) should reveal the Atlantic stingray paper. The stingray paper also considered the mechanisms of sensing, particularly whether or not the rays detect absolute field strength or field gradients: their findings suggest field gradients.

Josh H
PS: I have now received everyone's assignments, they are now awaiting marking (like good little assignments). Thank you.