Welcome to the I Can't Sleep Podcast,
Where I help you drift off one fact at a time.
I'm your host,
Benjamin Boster,
And today's episode is about the capybara.
The capybara,
Or greater capybara,
Is the largest living rodent,
Native to all countries in South America,
Except Chile.
Together with the lesser capybara,
It constitutes the genus Hydracurus.
Its other close relatives include guinea pigs and rock cavies,
And it is more distantly related to the aguchi,
The chinchilla,
And the nutria.
The capybara inhabits savannas and dense forests and lives near bodies of water.
It is a highly social species and can be found in groups as large as 100 individuals,
But usually lives in groups of 10-20 individuals.
Its common name is derived from tupi,
Kaapiwara,
A complex agglutination of ka'a,
Leaf,
Plus p,
Slender,
Plus u,
Eat,
Plus ara,
A suffix for agent nouns,
Meaning one who eats slender leaves,
Or grass eater.
The genus name Hydracurus comes from Greek haidour,
Water,
And kairos,
Pig,
Hog,
And the species name Hydracurus comes from Greek haidour,
Water,
And kairo,
Feel happy,
Enjoy.
The capybara and the lesser capybara both belong to the subfamily Hydracurenae,
Along with the rock cavies.
The living capybaras and their extinct relatives were previously classified in their own family Hydracuridae.
Since 2002,
Molecular phylogenetic studies have recognized a close relationship between Hydracurus and Caridon,
The rock cavies,
Supporting placement of both genera in a subfamily of cavity.
The capybara has a heavy barrel-shaped body and short head,
With reddish-brown fur on the upper part of its body that turns yellowish-brown underneath.
Its sweat glands can be found in the surface of the hairy portions of its skin,
An unusual trait among rodents.
The animal lacks down hair,
And its guard hair differs little from over hair.
Adult capybaras grow to 106-134 cm in length,
Stand 50-62 cm tall at the withers,
And typically weigh 35-66 kg,
With an average in the Venezuelan llanos of 48.
9 kg.
Females are slightly heavier than males.
The top recorded weights are 91 kg for a wild female from Brazil,
And 73.
5 kg for a wild male from Uruguay.
Also an 81 kg individual was reported in Sao Paulo in 2001 or 2002.
Capybaras have slightly webbed feet and vestigial tails.
Their hind legs are slightly longer than their forelegs.
They have three toes on their rear feet,
And four toes on their front feet.
Their muzzles are blunt,
With nostrils,
And the eyes and ears are near the top of their heads.
Capybaras are semi-aquatic mammals,
Found throughout all countries of South America except Chile.
They live in densely forested areas near bodies of water,
Such as lakes,
Rivers,
Swamps,
Ponds,
And marshes,
As well as flooded savannah and along rivers in the tropical rainforest.
They are superb swimmers,
And can hold their breath underwater for up to five minutes at a time.
Capybara have flourished in cattle ranches.
They roam in high ranges,
Averaging 10 hectares,
In high-density populations.
Many escapees from cavity can also be found in similar watery habitats around the world.
Sightings are fairly common in Florida,
Although a breeding population has not yet been confirmed.
In 2011,
One specimen was spotted on the central coast of California.
These escaped populations occur in areas where prehistoric capybaras inhabited.
Capybaras are herbivores,
Grazing mainly on grasses and aquatic plants,
As well as fruit and tree bark.
They are very selective feeders,
And feed on the leaves of one species,
And disregard other species surrounding it.
They eat a greater variety of plants during the dry season,
As well as fruit and vegetables.
This is because fewer plants are available.
While they eat grass during the wet season,
They have to switch to more abundant reeds during the dry season.
Plants that capybaras eat during the summer lose their nutritional value in the winter,
So they are not consumed at that time.
The capybara's jaw hinge is not perpendicular,
So they chew food by grinding back and forth,
Rather than side to side.
Capybaras are autocoprophagous,
Meaning they eat their own feces as a source of bacterial gut flora to help digest the cellulose in grass that forms their normal diet.
And to extract the maximum protein and vitamins from their food.
They also regurgitate food to masticate again,
Similar to cud chewing by cattle.
Like other rodents,
A capybara's front teeth grow continually to compensate for the constant wearing from eating grasses.
Their cheek teeth also grow continuously.
Like its relative the guinea pig,
The capybara does not have the capacity to synthesize vitamin C.
And capybaras not supplemented with vitamin C in captivity have been reported to develop gum disease as a sign of scurvy.
The maximum lifespan of the capybara is 8 to 10 years,
But in the wild capybaras usually do not live longer than 4 years because of predation from South American big cats,
Such as jaguars and cougars,
And from non-mammalian predators such as caimans and green anacondas.
Capybaras are gregarious.
While they sometimes live solitarily,
They are more commonly found in groups of around 10 to 20 individuals,
With 2 to 4 adult males,
4 to 7 adult females,
And the remainder juveniles.
Capybara groups can consist of as many as 50 or 100 individuals during the dry season when the animals gather around available water sources.
Males establish social bonds,
Dominance,
Or general group consensus.
They can make dog-like barks when threatened or when females are herding young.
Though quite agile on land,
Capybaras are equally at home in the water.
They are excellent swimmers and can remain completely submerged for up to 5 minutes,
An ability they use to evade predators.
Capybaras can sleep in water,
Keeping only their noses out.
As temperatures increase during the day,
They wallow in water and then graze during the late afternoon and early evening.
They also spend time wallowing in mud.
They rest around midnight and then continue to graze before dawn.
Capybaras communicate using barks,
Chirps,
Whistles,
Huffs,
And purrs.
Capybaras have adapted well to urbanization in South America.
They can be found in many areas,
In zoos and parks,
And may live for 12 years in captivity,
More than double their wild lifespan.
They are docile and usually allow humans to pet and hand-feed them,
But physical contact is normally discouraged,
As their ticks can be vectors for Rocky Mountain spotted fever.
The European Association of Zoos and Aquaria asked Droselus Park in Alfrestran,
Sussex,
England to keep the studbook for capybaras to monitor captive populations in Europe.
The studbook includes information about all births,
Deaths,
And movements of capybaras,
As well as how they are related.
In Japan,
Izu Shaboten Zoo and other zoos provide hot spring baths for capybaras.
Video clips of the bathing capybaras have millions of views.
These capybaras spawned a series of merchandise,
Such as plush toys,
And provided inspiration for the anime character Capybara-san.
Capybaras have become a figure in meme culture in the 2020s.
Common meme formats pair capybaras with the song After Party by Don Toliver.
In addition,
A song about capybaras was released and made popular on TikTok in 2022.
Capybaras have gained a reputation as a symbol of calm due to their perceived unflappability.
A fur is a soft,
Thick growth of hair that covers the skin of almost all mammals.
It consists of a combination of oily guard hair on top and thick underfur beneath.
The guard hair keeps moisture from reaching the skin.
The underfur acts as an insulating blanket that keeps the animal warm.
The fur of mammals has many purposes,
Protection,
Sensory,
Waterproofing,
And camouflaging,
With the primary purpose being thermoregulation.
The types of hair include Definitive,
Which may be shed after reaching a certain length.
Vibracy,
Which are sensory hairs and are most commonly whiskers.
Pellage,
Which consists of guard hairs,
Underfur,
And on-hair.
Spines,
Which are a type of stiff guard hair used for defense in,
For example,
Porcupines.
Bristles,
Which are long hairs usually used in visual signals,
Such as the mane of a lion.
Belly,
Often called down fur,
Which insulates newborn mammals.
And wool,
Which is long,
Soft,
And often curly.
Hair length is unimportant in thermoregulation,
As some tropical mammals,
Such as sloths,
Have the same fur length as some arctic mammals,
But with less insulation.
And conversely,
Other tropical mammals,
With short hair,
Have the same insulating value as arctic mammals.
The denseness of fur can increase an animal's insulation value,
And arctic mammals especially have dense fur.
For example,
The muskox has guard hairs measuring 30 centimeters,
As well as a dense underfur,
Which forms an airtight coat,
Allowing them to survive in temperatures of negative 40 degrees Celsius.
Some desert mammals,
Such as camels,
Use dense fur to prevent solar heat from reaching their skin.
Allowing the animal to stay cool.
A camel's fur may reach 70 degrees Celsius in the summer,
But the skin stays at 40 degrees.
Aquatic mammals,
Conversely,
Trap air in their fur to conserve heat by keeping the skin dry.
Mammalian coats are colored for a variety of reasons.
The majority's selective pressures include camouflage,
Sexual selection,
Communication,
And physiological processes,
Such as temperature regulation.
Camouflage is a powerful influence in many mammals,
As it helps to conceal individuals from predators or prey.
Aposematism,
Warning off possible predators,
Is the most likely explanation of the black and white pellage of many mammals,
Which are able to defend themselves,
Such as in the foul-smelling skunk,
And the powerful and aggressive honey badger.
In arctic and subarctic mammals,
Such as the arctic fox,
Colored lemming,
Stoat,
And snowshoe hare,
Seasonal color change between brown in summer and white in winter is driven largely by camouflage.
Differences in female and male coat color may indicate nutrition and hormone levels,
Important in mate selection.
Some arboreal mammals,
Notably primates and marsupials,
Have shades of violet,
Green,
Or blue skin on parts of their bodies,
Indicating some distinct advantage in their largely arboreal habitat,
Due to convergent evolution.
The green coloration of sloths,
However,
Is a result of a symbiotic relationship with algae.
Coat color is sometimes sexually dimorphic,
As in many primate species.
Coat color may influence the ability to retain heat,
Depending on how much light is reflected.
Mammals with darker colored coats can absorb more heat from solar radiation and stay warmer.
Some smaller mammals,
Such as voles,
Have darker fur in the winter.
The white pigmentless fur of arctic mammals,
Such as the polar bear,
May reflect more solar radiation directly onto the skin.
The term pellage,
First known use in English circa 1828,
Is sometimes used to refer to an animal's complete coat.
The term fur is also used to refer to animal pelts that have been processed into leather with their hair still attached.
The words fur or furry are also used more casually to refer to hair-like growths or formations,
Particularly when the subject being referred to exhibits a dense coat of fine,
Soft hairs.
If layered rather than grown as a single coat,
It may consist of short down hairs,
Long guard hairs,
And in some cases medium on hairs.
Mammals with reduced amounts of fur are often called naked,
As with the naked mole rat,
Or hairless,
As with hairless dogs.
Fur may consist of three layers,
Each with a different type of hair.
Down hair,
Also known as underfur,
Undercoat,
Underhair,
Or ground hair,
Is the bottom or inner layer composed of wavy or curly hairs with no straight portions or sharp points.
Down hairs,
Which are also flat,
Tend to be the shortest and most numerous in the coat.
Thermoregulation is a principal function of the down hair,
Which insulates a layer of dry air next to the skin.
The on hair can be thought of as a hybrid,
Bridging the gap between the distinctly different characteristics of down and guard hairs.
On hairs begin their growth much like guard hairs,
But less than halfway to their full length on hairs start to grow thin and wavy like down hair.
The proximal part of the on hair assists in thermoregulation like the down hair,
Whereas the distal part can shed water like the guard hair.
Mammals with well-developed down and guard hairs also usually have large numbers of on hairs,
Which may even sometimes be the bulk of the visible coat.
Guard hair,
Or overhair,
Is the top or outer layer of the coat.
Guard hairs are longer,
Generally coarser,
And have nearly straight shafts that protrude through the layer of softer down hair.
The distal ends of the guard hair is the visible layer of most mammal coats.
This layer has the most marked pigmentation and gloss,
Manifesting as coat markings that are adapted for camouflage or display.
Guard hair repels water and blocks sunlight,
Protecting the undercoat and skin in wet or aquatic habitats,
And from the sun's ultraviolet radiation.
Guard hairs can also reduce the severity of cuts or scratches to the skin.
Many mammals,
Such as the domestic dog and cat,
Have a pylomotor reflex that raises their guard hairs as part of a threat display when agitated.
Hair is one of the defining characteristics of mammals.
However,
Several species or breeds have considerably reduced amounts of fur.
These are often called naked or hairless.
Some mammals naturally have reduced amounts of fur.
Some semi-aquatic or aquatic mammals,
Such as cetaceans,
Pinnipeds,
And hippopotamuses,
Have evolved hairlessness,
Presumably to reduce resistance through water.
The naked mole rat has evolved hairlessness perhaps as an adaptation to their subterranean lifestyle.
Two of the largest extant terrestrial mammals,
The elephant and the rhinoceros,
Are largely hairless.
The hairless bat is mostly hairless,
But does have short,
Bristly hairs around its neck,
On its front toes,
And around the throat sac,
Along with fine hairs on the head and tail membrane.
Most hairless animals cannot go in the sun for long periods of time or stay in the cold for too long.
Marsupials are born hairless and grow out fur later in development.
Humans are the only primate species that have undergone significant hair loss.
The hairlessness of humans compared to related species may be due to loss of functionality in the pseudogene KRTHAP1,
Which helps produce keratin.
Although the researchers dated the mutation to 240,
000 years ago,
Both the Altai Neanderthal and Denisovan peoples possess the loss-of-function mutation,
Indicating it is much older.
Mutations in the gene HR can lead to complete hair loss,
Though this is not typical in humans.
At times when a hairless domesticated animal is discovered,
Usually owing to a naturally occurring genetic mutation,
Humans may intentionally inbreed those hairless individuals and,
After multiple generations,
Artificially create hairless breeds.
There are several breeds of hairless cats,
Perhaps the most commonly known being the Sphinx cat.
Similarly,
There are some breeds of hairless dogs.
Other examples of artificially selected hairless animals include the hairless guinea pig,
Nude mouse,
And the hairless rat.
The webbed foot is a specialized limb with interdigital membranes,
Webbings,
That aids in aquatic locomotion,
Present in a variety of tetrapod vertebrates.
This adaptation is primarily found in semi-aquatic species and has convergently evolved many times across vertebrate taxa.
It likely arose from mutations in developmental genes that normally cause tissues between the digits to apoptosis.
These mutations were beneficial to many semi-aquatic animals because the increased surface area from the webbing allowed for more swimming propulsion and swimming efficiency,
Especially in surface swimmers.
The webbed foot also has enabled other novel behaviors like escape responses and mating behaviors.
A webbed foot may also be called a paddle to contrast it from a more hydrofoil-like flipper.
A webbed foot has connecting tissue between the toes of the foot.
Several distinct conditions can give rise to webbed feet including interdigital webbing and syndactyly.
The webbing can consist of membrane,
Skin,
Or other connective tissue and varies widely in different taxa.
This modification significantly increases the surface area of the feet.
One of the consequences of this modification in some species,
Especially birds,
Is that the feet are a major location for heat loss.
In birds,
The legs utilize counter-current heat exchange so that blood reaching the feet is already cooled by blood returning to the heart to minimize this effect.
Webbed feet take on a variety of different shapes.
In birds,
The webbing can even be discontinuous as seen in low bait-footed birds like reebs.
However,
One of the most common is the delta or triangular shape seen in most waterfowl and frogs.
This delta wing shape is a solution that has convergently evolved in many taxa and is also used in aircraft to allow for high lift forces at high attack angles.
This shape allows for the production of large forces during swimming through both drag-based and lift-based propulsion.
Webbed feet are a compromise between aquatic and terrestrial locomotion.
Aquatic control surfaces of non-piscine vertebrates may be paddles or hydrofoils.
Paddles generate less lift than hydrofoils and paddling is associated with drag-based control surfaces.
The roughly triangular design of webbed feet with a broad distal end is specialized to increase propulsive efficiency by affecting a larger mass of water over generating increased lift.
This is in contrast to a more hydrofoil-like flipper of many permanently aquatic animals.
Webbed feet are the result of mutations in genes that normally cause interdigital tissue between the toes to apoptosis.
Apoptosis,
Or programmed cell death,
In development,
Is mediated by a variety of pathways and normally causes the creation of digits by death of tissue separating the digits.
Different vertebrate species with webbed feet have different mutations that disrupt this process indicating that the structure arose independently in these lineages.
In humans,
Syndactyly can arise from as many as nine unique subtypes with their own clinical,
Morphological,
And genetic fingerprints.
In addition,
The same genetic mutations can underlie different phenotypic expressions of syndactyly.
While these conditions are disorders in humans,
The variability in genetic cause of webbed digits informs our understanding of how this morphological change arose in species where webbed feet were selectively advantageous.
These conditions also demonstrate a variety of genetic targets for mutation resulting in webbed feet,
Which may explain how this homologous structure could have arisen many times over the course of evolutionary history.
One pathway implicated in interdigital necrosis is the bone morphogenetic protein BMP signaling pathway.
BMP signaling molecules are expressed in the tissue regions between digits during development.
In experiments with chickens,
Mutations to a BMP receptor disrupted the apoptosis of interdigital tissue and caused webbed feet similar to ducks to develop.
In ducks,
BMPs are not expressed at all.
These results indicate that in avian lineages,
The disruption of BMP signaling in interdigital tissue caused webbed feet to arise.
The magnitude of attenuation in this pathway is correlated with the amount of interdigital tissue preserved.
Other genetic changes implicated in webbed feet development in avians include reduction of TGF-beta-induced chondrogenesis and reduction of MSX-1 and MSX-2 gene expression.
Webbed feet could also arise due to being linked to other morphological changes without a selective advantage.
In salamanders,
Webbed feet have arisen in multiple lineages but in most do not contribute to increased function.
However,
In the cave salamander species,
Bigfoot,
Splayfoot salamander,
Their webbed feet are morphologically unique from other salamanders and may serve a functional purpose.
This demonstrates that webbed feet arise from developmental changes but do not necessarily correlate with a selective advantage functionality.
