By: Ella Iwalewa U.
Electroreception is the ability of organisms to detect naturally occurring electric signals in their environment. It is observed in some vertebrates including electric fishes and monotremes (e.g Platypus). Electroreception was initially discovered by Hans W. Lissman after observing weak electric discharges from the tail of an African Freshwater fish, Gymnarchus niloticus (African Knifefish). He also observed that the fish was responding to the glass and metal rods at a distance of about 10cm without amplified visual and chemical signals. He termed the process ‘electrolocation,’ after the term ‘echolocation,’ which means to send sound signals to the environment in order to identify objects that respond to that sound. Echolocation is commonly exhibited by bats when on the lookout for prey.
As a result of high air resistance, electroreception is more common in aquatic/amphibious beings than terrestrial beings. Thus, humans do not have electroreceptors but can feel strong electric stimuli if in direct contact with electric currents (which can result in shock or electrocution, so please don’t try this!). As of now, only the Platypus, Echidna, and Guiana dolphins possess electroreceptors.
We may be familiar with the cartoon Phineas and Ferb, and the iconic character, Perry the Platypus, but are we familiar with how platypuses survive? The platypus, aka duck-bill, is a monotreme (has mammary glands and still lays eggs). It was first discovered in Sydney, Australia, centuries ago by the governor of the state. The platypus is a nocturnal animal, which means it performs most of its activities at night. A characteristic of the Platypus is its ability to detect electric currents discharged in deep waters without sight, hearing, or smell (electroreception). It is the only member of the Ornithorhynchidae, and it is one of three mammals that are able to detect electric signals underwater using electric impulses. (Calling a platypus a mammal has always been controversial as a result of its aquatic abilities, so it's more referred to as a semi-aquatic/amphibian animal.) Similarly, the terrestrial Echidna exhibits this unique trait, and together with the platypus, they form the order Monotremata.
The platypus’ eyes, nostrils, ear canals are all closed underwater, so it uses its electro-mechanoreceptors to detect food. There are 3 bill sensors: a push-rod mechanoreceptor, a serous electroreceptor, and a larger mucous receptor. The function of the mechanoreceptor is to detect mechanical stimuli in the environment like touch and pressure and relay it to the platypus’ central nervous system (CNS), while the electroreceptors enable the platypus to detect electric signals generated by objects (or prey) in its environment. The platypus’ duck-shaped bill has 40,000 electroreceptors on its stripes and 60,000 mechanoreceptors. So, while the information to the brain when the stimulus is detected is performed collectively, the platypus detects mechanical impulses and electric signals. This has enabled the platypus to navigate deep, dark waters without the aid of audio-visual senses and determine the location of prey and predators as well. What makes the platypus so unique is the fact that it can easily navigate the water while being a mammal and find food for itself through electrolocation. The platypus also has a large number of electro-mechanoreceptors that make it possible for it to detect signals over a large surface area. The mechanoreceptors help to estimate the distance the platypus is from the prey by determining the difference between the electric signal and pressure stimuli in the water. Experiments have been conducted to show that it reacts to even artificial electric signals placed on prey. Its food-finding is largely dependent on electroreception because all other senses are turned off.
Unfortunately, there has been a decline in the population (roughly two hundred to three thousand currently) of the platypus’ as a result of climate change, human interference, and loss of habitats. There is still much to discover about platypuses, their unique physical structure, how their electroreceptive evolution came to be, and ways by which their possible extinction can be stopped.
QUESTIONS
What is electroreception?
Electroreception is the ability of an organism to determine electrical impulses in the environment using electroreceptors on its body. It’s used for electrolocation and electrocommunication. It’s found mostly in aquatic, amphibious animals because water is a good conductor of electricity.
What is a unique feature of platypus?
Its duck-shaped bill and webbed feet, beaver-like tail, and otter-like body and fur.
Why do platypuses depend on electrolocation to find their prey? Well, when a platypus is submerged in water, all its senses are temporarily turned off, so it uses its electroreceptors and mechanoreceptors to determine the presence and location of prey. As a result of its large number of receptors, it moves directionally towards its prey. It has been observed that the side by side sway of a platypus head is caused when it senses prey.
Sources:
Citation: Langner G., Scheich H. (2009) Electric Senses in Monotremes: Electroreception and Electrolocation in the Platypus and the Echidna. In: Binder M.D., Hirokawa N., Windhorst U. (eds) Encyclopedia of Neuroscience. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-29678-2_2919” https://link.springer.com/referenceworkentry/10.1007/978-3-540-29678-2_2919
Reed Platypus Electroreception: https://www.reed.edu/biology/professors/srenn/pages/teaching/web_2007/myp_site/ontogeny.html
Platypus on Wikipedia: https://en.wikipedia.org/wiki/Platypus
Image Credit:
No changes were made, 2013-12-22-19-48-27-G11-IMG_1612 | Drew Stemen | Flickr, License: Creative Commons Legal Code