The Insane Biology of: The Platypus

when the platypus first came to the attention of european scientists in 1798 not everyone was convinced that the creature before them was even real some thought a prankster had mashed together separate parts of different animals to create a fake not an uncommon occurrence at this boom time of natural discovery but the platypus was a very real animal and one that confused anatomists for some time a creature with fur a bill and webbed feet that lays eggs and can secrete venom was this a mammal a duck some sort of furry reptile these european scientists were asking the same questions that the aboriginal people of australia had been asking for a long time before them there are several aboriginal stories about the origins of the platypus one of which tells of a union between a duck and a water rat in science terms we've ultimately classed the platypus as a mammal or more specifically a monotreme an egg-laying mammal of which there are only two kinds of animals in the world and this along with its other rather reptilian traits has made scientists scratch their heads for a long time where does the platypus fit exactly on the tree of life as continents divided and the branches of the tree of life diverged the platypus seems to have taken its own very special route but just like with all animal adaptations there has to be some purpose to all the platypus's strangeness but what evolutionary question was this the right answer to if you look back in any textbook the definition of a mammal is a warm-blooded vertebrate animal that has fur secretes milk and typically gives birth to live young typically being the key word there platypuses are one of only two mammals that lays eggs the other is the only other monotreme the echidna of which there are four species when it's time to lay the eggs female platypuses dig their burrows crawl in and seal themselves up here they lay their eggs curling them between body and tail until they hatch 10 days later from here the platypus acts like most other mammals nursing their young on milk for three to four months until they're capable of swimming solo to understand how and why this egg-laying ability exists in a mammal we need to wind back the clock a long long time around 340 million years ago the first amniotes appeared on earth in the form of small lizard-like creatures amniotes are four-legged vertebrates that are defined by the membrane or amnion that protects the embryo during development the amniotic egg was an evolutionary invention that first allowed reptiles to colonize dry land fish and amphibians must lay their eggs in water and therefore can't live far from water but thanks to the amniotic egg reptiles can lay their eggs nearly anywhere on dry land soon amniotes spread far and wide around earth's land and became the dominant land vertebrates and around 315 million years ago they split into the two major groups of four-legged vertebrates which still exist today one branch contains the modern reptiles and birds the other included the mammal-like reptiles from which modern mammals later evolved this branch of mammals eventually developed to have the amniotic egg grow inside the mother's womb giving rise to internal pregnancies but one branch of mammals did not follow suit the monotremes or egg-laying mammals split off from the mammalian lineage around 200 million years ago they never gained the ability to have an internal pregnancy and never lost their egg laying ability genome sequencing of platypus sex cells have shown there are a large number of shared genes between platypuses and birds in particular the platypus retains copies of the vitella ginnin gene which codes for egg protein that is a precursor to egg yolk which in turn helps sustain growing embryos platypuses have fewer copies of the gene than birds in reptiles but most mammals don't have the gene at all this means the platypus has the ability to lay eggs but that their young are perhaps less reliant on egg protein than birds and reptiles this makes sense when we remember that platypuses also feed their young via lactation after hatching their laying of eggs is a sort of hangover from their reptilian ancestors and for a while it served them well the monotremes were the dominant mammals on what is now the continent of australia for a long time that is until they got swept aside by the arrival of their marsupial cousins marsupials originated in what is now south america and migrated over to what is now australia via the supercontinent gondwana around 70 million years ago their bodies were more efficient at locomotion and their internal pregnancies meant they could better protect their young and thus they out-competed the monotremes on almost every front and slowly all but two the echidna and the platypus went extinct so the question is why did they survive when the rest did not one hypothesis as to how the platypus persisted in the face of intense competition from the marsupials is its ability to take to the water a domain where the marsupials could not follow the echidna's earlier ancestor too is thought to have been semi-aquatic even though it's not anymore marsupials could not colonize water environments because when they're born they have to live inside their mother's pouch for weeks to suckle milk the babies would drown if their mothers ever had to venture into the water but with their eggs secure in a nest the platypus can happily stay in the water avoiding predation from the marsupials and exploiting their very own environmental niche the platypus is an expert swimmer its ability to hunt below the water is down to a few key features of its physiology the platypus's webbed feet help power them through the water using their front feet for paddling their back feet for steering and a feature that helps the platypus stay submerged for up to two minutes at a time is its ability to become watertight when necessary it has folds of skin that cover its ears and it can close its nostrils too and despite its hunting prowess underwater it nearly completely closes its eyes when diving thanks to a sixth sense that almost no other mammal possesses it doesn't need to see to hunt one of the most distinct parts of the platypus is its bill its iconic shape is wide and flat but unlike a duck spill the platypus bill is described as flexible rubbery and a little fleshy its surface supposedly feels a bit like suede and the bill is the platypus's primary hunting tool it can hunt with its eyes completely closed because it's super sensitive in two key ways it's mechanoreceptive and electroreceptive mechanoreceptive means sensitive to external mechanical stimulus such as touch or pressure in the case of the platypus its bill contains mechanoreceptors called push rods these are columns of densely packed cells that move independently of surrounding skin when pressure or a vibration is applied to the push rod it triggers the nerve at the bottom of the column the pressure doesn't have to be large the slightest tremors can be felt through the water the bill is so sensitive it can detect fresh water shrimp from a distance of 15 to 20 centimeters away simply by sensing movements in the water the other sensing ability of the bill is its electro-reception all animals emit electric signals from their muscles when moving and the platypus bill can sense these electric fields originating from their prey the bill contains around 70 000 glands that assist in the electroreceptive function of the bill the mechanism of electroreception in the bill is much like that of the elasmobranks like the hammerhead shark the electrical currents from the stimulus travel through the water and then through secretions from the glands in the bill which surround nerve endings beneath the bill's surface the one hundred thousand electro and mechanoreceptors on the platypus bill are arranged in a beautiful striped pattern with bands of electro and mechanoreceptors alternating electroreception is common in fish but has only been found in three mammals to date the platypus the echidna and the guyana dolphin platypus bills have up to 70 000 electro receptors and those of long build and short build echidnas have only 2 and 400 respectively you can see evolution in progress here since moving back onto land the electro receptors of the echidnas are being selected against because such sensing ability is only useful in semi-aquatic environments but this electroreception is not a remnant from an early fishier ancestor it evolved completely independently of electric fish and is the answer two different lineages came up with to a similar evolutionary pressure electroreception isn't the only feature of the platypus that's rarely seen in mammals next time you pick up a platypus you'd be wise to keep its back legs pointing out of reach male platypuses have spurs on the back of their hind feet that connect to venom glands in their abdomen and that while not deadly to humans can have some pretty nasty side effects nausea cold sweats lymph nodes swelling and immediate excruciating pain that can't be relieved through normal painkillers venomous mammals are now pretty rare there are only a handful that we know of such as the slow loris the only known venomous primate which uses venom to protect itself against predators or the american short-tailed shrew which uses its venom to immobilize its insect prey it's thought that with the development of teeth and claws most mammals developed much faster ways of killing prey than venom which needs time to take effect and so venomous capabilities became evolutionarily redundant of the mammals that kept their venom the very different methods of delivery suggest the ability evolved independently take the slow lorises mentioned earlier they can look pretty cute when they raise their arms in the air as if they're asking for a hug but don't be fooled this is actually how they access their venom it's produced by glands in their armpits which they lick the venom mixes with their saliva and settles into grooves in their teeth ready to harm anything that the slow loris bites the short-tailed shrew also has grooves in its teeth but its venom comes ready made in the shrew's saliva both of which differ to the platypus which delivers its venom through its spurs but interestingly for the platypus a recent study found that many of the proteins present in its venom are the same as those found in reptile venom even though the reptiles split from mammals some 315 million years ago does this mean the venom is an evolutionary leftover from the platypus's reptilian ancestor or is it an example of independent convergent evolution of the venom by sequencing the platypus genome scientists found that the platypus's ability to deliver venom is down to a duplication in a set of reptilian genes the same reptilian genes that underwent the same duplication independently in snakes after reptiles and mammals split in the evolutionary tree this suggests then that platypus venom is an unlikely example of convergent evolution in this case reptiles and the platypus developed similar venoms despite not having a common ancestor for hundreds of millions of years scientists still don't know exactly why platypuses have venom spurs but it's thought that they use them in mating practices and to defend territory inmates from other platypuses despite its weirdness we now understand that the platypus is not just a funny-looking animal it's a highly adapted creature perfectly suited to its environment some of its bizarre features are remnants from an ancient time and others are more recent evolutionary inventions that happen to be similar to ones in the fish the birds and the reptiles it's a wild and unlikely mashup of traits that allows the platypus to sit on its very own branch of the evolutionary tree but we also know there's a lot more of the puzzle to put together scientists are constantly stumbling across new unusual findings about this amazing animal just last year researchers accidentally discovered that platypus skin glows under uv light why we still don't know there are likely many more secrets hiding within the platypus that we will continue to discover for years to come australia's unique landscape and geography made the platypus what it is today australia is literally teeming with biodiversity its patchwork of different climates from tropical forests to hostile deserts to tropical reefs along with its isolated nature has given rise to some of the world's strangest and most iconic creatures eighty percent of the plants and animals in australia are unique to australia found nowhere else on earth having grown up in america australia's animals seem downright alien to me and i love learning about their evolution and their sometimes wacky behavior to immerse yourself in 50 minutes of the beautiful weird and wonderful australian continent you should watch hidden australia on curiosity stream believe me i have spent my life watching nature documentaries and this one still showed me animals i never knew existed like what even is this guy this is such a fun film and will make you daydream about getting to visit such an incredible and diverse place curiosity stream is a streaming platform with thousands of high quality documentaries like this one and now curiosity stream has partnered with us to offer an incredible deal by signing up to curiositystream you now also get a subscription to nebula nebula is a streaming platform made by me and several other educational youtube content creators it's a place where we can upload our videos and podcasts ad free and a place where we can experiment with new original content by signing up to the bundle deal you'll get access to both curiosity stream and nebula where you can access originals like joe scott's original series called mysteries of the human body with episodes like real human oddities from history or the strangest epidemics of all time or you can watch 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Channel: Real Science

Views: 1,930,300

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Id: Wh2du5SOjmY

Length: 16min 7sec (967 seconds)

Published: Sat Jun 26 2021