platypus-swimming-closeup

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Backround

The Platypus is a semiaquatic, egg laying mammal native to eastern australia. Together with the four species of echidnas, it is one of the five members of the order monotremata. Echidna are also long-billed and short-billed. Monotremes are the only mammals that lay eggs, the reason being that they were the earliest offshoot of the mammalian family tree. Monotremes are thought to have split from other mammals approximately 166 million years ago. As adults males and females are relatively the same size, males being slightly larger than females. However males have a venomous spine located on their left hind ankle. This venom is used not to kill prey like most other animals, it is instead used during the mating season to establish dominance. This evidence is backed up by the fact that males produce more venom during the mating season than any other time of the year. Platypus are exclusively carnivores and use a combination of electroreception and vibration detection to find prey, as explained below.

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*This figure depicts the number of electroreceptors found in the bill of each species of monotreme.

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*This figure shows the platypus’s range of electroreception. Demonstrating the fractions of millivolts it can detect at certain distances.

Electrolocation and mechanical senses:

Monotremes are the only mammals that use electroreception to find prey.  This method of foraging is extremely effective because the platypus feeds exclusively on other animals. And since live prey produce electrical impulses stemming from the nervous system, it makes it very easy for the platypus to find food, even when it’s buried under the substrate. This method of locating food is highly developed, as the platypus closes its eyes and ears when underwater.

The electroreceptors are located in rostrocaudal rows in the skin of the bill and are made up of sensitive mucous glands, the platypus can determine the direction of an electrical source by comparing differences in signal strength across the sheet of electroreceptors, this explains why they move their head from side to side while foraging. [Groves pg. 1132].

The platypus also has another very sensitive method of detecting prey, mechanoreceptors. Mechanoreceptors are clusters of extremely sensitive epidermal cells, called push-rod mechanoreceptors. These clusters of epidermal cells are extremely sensitive to vibrations in the water, and are used alongside the electroreceptors to find prey. The mechanoreceptors are distributed uniformly across the bill, allowing the platypus to detect movement from all sides. Electroreceptors are linked to the trigeminal cranial nerve. Sir Everara Home was the first to discover the trigeminal nerves, which are the nerves that supply sensory stimuli to the brain from face, teeth, and the tongue. Platypus electroreception was first demonstrated in Australia and the detection strengths were measured 300 vper cm. Electroreception explains the accurate navigation through light-limited areas.

There are about 40,000 electroreceptors and 60,00 mechanoreceptors located in the bill. [Pettigrew pg. 1200]

Along with the use of electroreceptors to detect movement, the platypus uses the mechanoreceptors to also detect movement, but of a different kind. When a prey moves it emits electrical impulses as well as mechanical pressure changes, travelling back to the platypus. The platypus uses the difference in arrival times of the two signals to detect distance between itself and its prey. [Proske pg. 1189]

Fun fact: the platypus can detect electrical signals as low as 20mV per cm.

Bibliography

Groves, C.P. (2005). “Order Monotremata”. In Wilson, D.E.; Reeder, D.M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press

Proske, Uwe; Gregory, J. E.; Iggo, A. (1998). “Sensory receptors in monotremes”. Philosophical Transactions of the Royal Society of London pg. 1187-1198

Pettigrew, John D.; Manger, P.R.; Fine, S.L. (1998). “The sensory world of the platypus”. Philosophical Transactions of the Royal Society of London. 353 (1372): 1199–1210

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5 thoughts on “Electroreception In Platypus

  1. So interesting – I did’t know this about electrolocation. This pictures in the beginning are awesome – maybe some more towards the end? Great job!

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  2. I really enjoyed reading the electroreceptors found in the bill, and the picture showing the range of their electroreception. My only critique would be to maybe add some more in text citations to some of the paragraphs without them, and maybe distribute some more pictures to the end. I really enjoyed reading this though, and it wa so interesting. Good job!

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  3. I really like this post about the platypus. I never really looked into platypuses as well as their foraging behavior. So neat how different organisms across the planet use special senses to live and catch their prey. I like how you added photos in the beginning. Maybe more in-text citations since they seem so spread out as well as attributing the photos you have. The second playpus picture is a little blurry from my perspective. Overall I think this blog post is really interesting and informative!

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  4. I had no idea that platypuses had that type of sense, this was very interesting. I also liked that you included the picture explaining how it works with them. the picture helped the reader understand the sense better and overall I found this very interesting. Good Job!

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  5. You have some really great pictures and diagrams in this to help explain the electroreception sense the platypus has. I think you mean to say 60,000 in one of your last paragraphs. Is there any studies done by researchers involving the study or use of this sense. Good start.

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