The Insane Biology of: Sloths

this episode is brought to you by curiositystream and nebula where you can watch the next episode of our brand new series becoming human and a field notes companion video about the hilarious reality of studying sloths in the field the rainforest is a beautiful but deadly place it's an ecosystem with immensely High biodiversity and intense competition plants battle for sunlight insects battle for territory most animals face the constant risk of predation death by disease poisoning from plants or a venomous bite this ecosystem is suited to only the hardiest most formidable creatures stay alive here many prey animals rely on speed teamwork or sheer Ingenuity and yet throughout the rainforests of Central and South America lives this creature not quick not collaborative and presumably not very smart sloths were first described in Western science by unimpressed French naturalist George Buffon in 1749 he wrote slowness habitual pain and stupidity are the results of this strange and bungled Confirmation these sloths are the lowest form of existence one more defect would have made their lives impossible those sloths are indeed cute at first glance they do have several traits that made Buffon think so little of them sloths spend their days in the Treetops barely moving when they do decide to move they crawl at a Breakneck pace of 15 feet per minute some sloths even spend their entire life in the same tree they were born in never bothering to venture in any direction for any reason to some their ongoing survival seems like an actual mistake as if an evolutionary blunder has allowed them to slip through the cracks but to view sloths as useless is to see them from a narrow human lens we humans equate Speed and Agility with adaptive Fitness since for our bipedal species these traits have been beneficial to survival in Our Minds The Reason something is slow is because it sucks at being fast that slowness is the inferior opposite to speed but sloths Force us to re-examine this paradigm for a sloth slowness isn't a defect but a feature and their slow paced lifestyle is in fact the perfect way for them to survive in their dense and chaotic habitat and the adaptations surrounding the slowness of sloths are really really strange from their metabolism to their slow rate of digestion to their limb muscles bones and fur no other animal is even remotely similar to the sloth because as strange as a sloth might appear on the outside it only gets weirder the closer you look [Music] modern tree sloths are masters of stealth a far cry from house sloths originated on this planet their unrecognizable compared to their ground sloth ancestors like megatherium americanum one of the largest land mammals to have ever existed weighing up to four tons and measuring up to 6 meters or 20 feet in length from head to tail sadly these giant sloths went extinct and today there are only six species of sloths all of them tree sloths from two different families the two-toed and three-toed sloths they live in or near canopies of tropical rainforests of Central and South America their slow stealthy movement essential in keeping them hidden from their predators such as jungle cats and Harpy eagles these Predators hunt largely with their eyesight so moving slowly and making no sudden movements helps to conceal the sloths but moving around high in the trees is no easy feat for any animal getting around safely requires strength agility and balance and it's an evolutionary challenge that has led to many different adaptive strategies among arboreal mammals some species of arboreal animal incorporate their tails into their movement or into their suspensory behaviors porcupines silky anteaters spider monkeys and opossums use a prehensile tail to grasp branches for extra support and stability other animals use speed and momentum to get around in the trees by a type of locomotion called brachiation it's used mainly by monkeys and apes and allows them to propel themselves through the canopy by swinging from one hold to another by the arms it's both fast and energy efficient by swinging like a pendulum potential and kinetic energy is exchanged back and forth a brachiating primate can make use of this conservation of momentum and the metabolic recovery of energy as it goes but this locomotor behavior requires a good deal of strength if you've ever tried to brachiate or arm swing as an adult like swing across the monkey bars or if you've ever attempted one of those hang for 100 seconds Carnival scams you've probably been disappointed by your performance to move around by your arms or to hang like this is hard but even more challenging than arm swinging brachiation would be to try to do the monkey bars slowly and even harder than hanging for 100 seconds would be hanging for 10 minutes with one hand sloths which have no supporting prehensile tail and do not use pendular exchanges of energy to make things easier for themselves do all of this routinely seemingly with the greatest of ease a sloth can easily suspend its entire body weight from a single limb for over 10 minutes they can brace themselves between two branches in the crucifix position for even longer so just by a back of the envelope calculation I worked out that a sloth is about two times stronger than your average human and yet when you look at their limb their muscles are thin and ropey they do not look like they would be that strong to understand the baffling strength of sloths I talked to Dr Mike Butcher professor of zoology and biomechanics at Youngstown State University their total body skeletal muscle mass is only roughly 23.5 to 24 percent compare that to you you're 44 percent so they have significantly less muscle so per gram of muscle tissue they're getting a lot of force out of their muscles so how are they able to perform such Feats of Strength by dissecting mapping weighing and measuring each of the 50 two muscles found in the forelimb of three-toed sloths researchers started to get closer to an answer they started by examining the four limb where there are two major groupings of muscles flexors and extensors flexors do work to bend a joint for example when you flex your biceps your elbow flexors contract and pull on the forearm segment creating a bending or rotational movement of the elbow joint to move your hand upwards flexor muscles are used for pulling Motions like doing a pull-up extensors serve the opposite function extending and straightening joints these types of muscles are generally used for pressing motions when you and me are walking we're an upright mammal we expect that our extensor muscles are the ones that are most important for keeping us upright and supporting our body weight but in sloths this story is totally flipped when you're upside down those muscle activations must change accordingly it's as if the nervous system has to rewire or retool itself to now use flexor muscles as the main supporting muscles in sloths the flexors are more well developed than the extensors this this means that the muscles that sloths use to grip and pull are larger than those that extend the researchers also found that the type of individual fibers within the muscle helps give the sloth remarkable grip strength the muscle fibers in the digital flexor musculature become progressively more angled towards the forefoot when the fibers are aligned in this way that is less parallel to the length of the muscle belly they can produce more Force this phenomenon is known as penation but it's not just how the sloth's muscles are built that gives them Incredible strength it's how they use them the force velocity relationship is a fundamental principle of skeletal muscle physiology the data in this curve shows an inverse relationship between force and velocity meaning that an increase in force would cause a decrease in velocity and vice versa and the faster that a muscle contracts we call that contractile velocity the less force that a muscle is capable of producing so what do you think the strategy is that sloths have adopted they can track their muscles very slowly so if you contract your muscle more slowly you're enhancing the amount of force that you can get out of them and it has the cost benefit of not consuming a lot of energy to contract your muscles slowly and forcefully for these reasons three-toed sloths have a relative grip strength that approximates 100 of their body weight by comparison the average grip strength for a human is around 25 to 45 percent of their body weight which may explain why we don't do so well in those hang for 100 seconds Carnival gimmicks with all these amazing adaptations sloths can move about the canopy with a surprising acrobatic Grace and hang for basically indefinite periods of time but things don't always go smoothly for the sloths Dr Becky Cliff is the founder of the sloth conservation foundation and has studied sloths for many years one of her projects examines sloth movement and behavior using small radio transmitter backpacks and when the project began she kept getting startling signals what we'd get back from the backpack data race would have these nice sloth climbing signals and then would have whoosh and you're like what has happened um and it took us a really long time to figure out what these crazy signals were but it was the sloth falling out the tree and each individual does it on average once a week for its entire life and they're not falling from a short height they're falling from like 100 meters in the air um and they bounced a little bit when they hit the floor and then they get up and they climb the tree again and they're absolutely fine but the sloths don't fall because they lose their grip they just miscalculate a bit on which branches to climb they like to eat the leaves on the very tips of the branches and these branches are very flimsy and don't often take their weight so they do often fall just by branches breaking and things luckily their ribs are remarkably flexible allowing them to survive these Falls the two-toed sloth even has 46 of them more than any other mammal for reference we have 24 but if it weren't for the sloth's strange diet they might not take these risks at all sloths are profoundly particular creatures even though there are hundreds of types of vegetation in tropical rainforests three-toed sloths usually only eat the leaves of a few types of trees and of these leaves they prefer the youngest leaves growing on the crowns of the trees eating leaves and leaves only is a pretty difficult way to get nutrition the leaves have a high proportion of hard to digest cellulose and mature leaves don't have many calories so how does this strategy work for them the key to it all is their four-chambered stomach the first three stomachs are fermentation Chambers where leaves are broken down by symbiotic bacteria the resulting product of that is then broken down in the fourth stomach by acids and enzymes this is a lot like how cows digest their food but usually fullivores compensate for the low calorie content of leaves by eating a lot of them and digesting them quickly but sloths don't have that option it can take up to 50 days for them to fully digest a single leaf and this slow digestion means they also only need to poop around once per week which they dutifully climb all the way down out of their tree to do one of the only reasons they would ever leave the trees and once they're doing their business they make sure to do it with style the poop dances um something that all sloths do when they go to the bathroom which they only do once a week so they climb down from their favorite tree they do the poop dance on the floor which it looks like they're twerking kind of in slow motion what they're actually doing is trying to dig a little hole using their bum so they wiggle around and then they poop in the hole and then they do another poop dance to bury it and they climb back up the tree but it does look absolutely ridiculous the reason for this Herculean effort just to poop is thought to be to conceal their scent poop raining down from the Treetops would leave a pretty big scent Trail leading Predators right to the perpetrator of that smell and even though they only poop once a week their stomach is literally always full they can't eat more until what's in their stomach has already passed so like with everything else they have to ingest their food slowly three-toed sloths have been observed to eat on average only 17 grams of food per day which is like three leaves per day eating such little food would make any other similarly sized mammal starve to death but sloths have another trick up their sleeve they have the slowest metabolism of any mammal in the animal kingdom rivaled only by mammals deep in hibernation having such a slow metabolism means that they have tremendously low energy needs three-toed sloths burn as little as 130 calories per day two toad sloths around 300 calories per day and their metabolism is even weirder than it seems on first glance the first weird thing is that sloths don't need to maintain a stable internal temperature like most other mammals instead their internal temperature changes with the temperature outside and it can fluctuate as much as 10 degrees Celsius this is more like how the ectotherms work like lizards aka the cold-blooded animals by allowing their body temperature to fluctuate with the temperature outside sloths save a lot of energy up to about 32 degrees Celsius sloths would have you convinced that they are cold-blooded creatures but any hotter than this point things get even weirder again as sloths do something different than any other animal they begin to actively depress their metabolism without entering a state of estivation as far as we know this is completely unique in the animal kingdom entering into estivation or hibernation would mean shutting almost everything down reducing the heart rate drastically reducing body temperature and becoming unresponsive it's a long and serious process for an animal to do this but sloths manage to reduce their metabolism quickly while they're awake and able to move around they can also do it for very short periods and can reverse it as soon as temperatures cool down by depressing their metabolism they are simultaneously saving energy and also reducing the amount of metabolic heat being produced by their body therefore staying a little bit cooler so are sloths ectotherms or endotherms the answer is neither or maybe both sloths exist in a transitional State between cold-bloodedness and warm-bloodedness a state called heterothermy and while saving energy in the form of moving slowly digesting slowly pooping infrequently clearly have their adaptive benefit they also have some surprising side effects side effects that look like a curious Quirk but in fact provide another layer of protection for the sloth staying hidden is the only way a sloth can survive and sloths have become true masters of camouflage their slow movements allow them to blend in with the swaying of branches and so does their Mossy green fur a fur so unique that it's its own microcosm of Abundant Life both types of sloths have a diverse collection of microorganisms in their fur including arthropods fungi and algae including some species that only exist within the ecosystem aboard the sloth the cryptoses moths or certain species of green algae only live in sloth fur individual hairs of three-toed sloths have unique cracks which allow the hair shaft to become saturated with rain water and allow algae to grow hydroponically the algae lives its life being passed directly from mother sloth to baby sloth and has not been found and anywhere else Beyond sloth fur and intriguingly in a roundabout way that silly sloth poop dance may play a crucial role in the growth of this algae when sloths descend to the ground and poop female kryptosis moths lay their eggs in the fresh excrement the larvae then develop entirely within the poop and adult moths emerge and fly to the canopy in search of their sloth fur home and these moths are crucial for the algae and sloth fur the moths likely transport nitrogen up from the piles of dung allowing the algae to grow and it turns out this algae is very important to the sloths they were recently found to actually consume their algae Gardens in order to supplement their limited diet without the poop dance there would be no moths and without the moths there would be no nitrogen and thus no algae and for researchers sloth poop may be the key for future research endeavors so one of the projects I'm working on at the moment is to try and train a dog to detect sloth poop and then we can start actually walking transects and being like oh this many sloths live in this area based on the number of poop piles on the floor um and for the first time we can start monitoring populations over time and see how it's changing and then we can show for the first time sloths are in trouble they are actually decreasing um because the current conservation statuses don't reflect that and that's based on a lack of data sloths are currently listed under the least concerned category because of this lack of data and without the hard science it's hard to protect these incredible animals it's so hard to get funding for an animal when they say oh it's loose concern and so really nobody cares but actually that's not true and what we're seeing here is sloths literally being decimated areas where I knew there were sloths living three years ago in really high densities and I've completely void our sloths so we're literally seeing it every single day and there's nothing like documenting this to the to governments or to The Wider Community to funders and donors there's just nothing out there lots of data tons of papers and hard numbers are going to be needed to ensure the survival of these incredible animals and on paper hard numbers like these are presented in the format of clean white paper with neat Black Ink but the way these hard numbers are collected is never that tidy field work is the beautiful and messy reality behind so much of the science we all know today I studied biology in college with law of hours spent in the lab and lots of hours writing up papers this was all well and good but it wasn't until my first field research trip to Indonesia that my soul was ignited every single day was filled with Adventure both good and bad I learned firsthand that to collect valuable data on the populations of critically endangered frogs it meant trekking Through Rivers at night stepping in heaps of vicious fire ants getting caught in powerful thunderstorms stumbling upon magnificent and enormous pythons this was the science that thrilled me and the people who do it for a living are some of the most fascinating people I have ever met their stories are literally insane from flesh-eating bacteria to homicidal elephants to naming new species and seeing sites no one has ever seen fieldwork is the backdrop for some of the most incredible stories I have ever heard and our new nebula plus series field notes aims to capture these exact stories I often talk about the science of incredible animals on this channel and now we will get to hear from the experts behind that science the people spending months years or decades in the field the people who know these animals better than anyone else on the planet I recently returned from Costa Rica where I had the amazing opportunity to witness the work going on to study and conserve sloths there from tracking the sloths to analyzing their muscle contractions to learning about all of the enormous efforts in the works to protect them it was a trip that opened my eyes to the very tricky and very rewarding world that is sloth science the video you just watched explains the science of sloths in the field notes episode will show you the sometimes hilarious reality of trying to get that science and since we've been ramping up production like there's no tomorrow we also have the next episode of becoming human available on nebula right now this one about the first tools our ancestors ever made once our ancestors became upright hands became free to start altering the world around them but the fossil record tells us that the evolutionary leap into tool making isn't as straightforward as you might think we are cranking out these nebula videos if you've ever considered signing up now is the time to do it foreign [Music]

Channel: Real Science

Views: 1,185,836

Keywords:

Id: BTRUqdH8IqQ

Length: 23min 48sec (1428 seconds)

Published: Sat Nov 12 2022