SciShow is supported by Squarespace. Whether you need a domain, website, or online
store, make it with Squarespace [ā©INTRO ] Itās pretty well known that Australia is
home to some strange animals ā everything from giant spiders to birds that can mimic
chainsaws. And most of them follow familiar patterns
in biologyā¦ except a tiny order called Monotremata, with only two subgroups: the echidnas and
the platypus. Monotremes are mammals, so they have mammary
glands and milk, theyāre covered in hair, and they can heat up their bodies. But monotremes also lay eggs. In fact, they have a bunch of weird adaptations,
and many scientists think that they branched off from other mammals, a long long time ago,
like 200 million years ago. So by taking a closer look at echidnas, we
can see how these unusual traits work and why they may have stuck around. Echidnas, like all monotremes, are missing
something most animals rely on to digest food. They donāt have stomachs. The digestive system is basically a series
of flesh bags with different secretions, enzymes, and bacteria. It breaks down food, absorbs the nutrients,
and gets rid of the waste. At least 450 million years ago, scientists
think that vertebrates were having trouble getting nutrients out of larger proteins in
their diets. So to cope with these big molecules, they
evolved a sack of super corrosive acid and other digestive enzymes ā a stomach. But, over millions of years, there were some
vertebrates that apparently didnāt need the extra help, like monotremes. Researchers have found that genes that code
for stomach acid and enzymes seem to have mutated to the point of being lost from their
genome. Echidnas mostly eat ants and termites, using
long sticky tongues to catch their prey, and a bony plate in their mouth to grind them
up. And even without stomachs, echidnas seem to
be surviving just fine. Maybe even better than fine, because they
live a ridiculously long time. There are reports of echidnas living up to
50 years in captivity, and over 40 in the wild. The platypus, for comparison, maxes out at
around 17 years in captivity. Scientists think this lifespan may be related
to how their bodies manage energy. Even though they can generate heat, monotremes
have some of the lowest body temperatures of any mammal. Humans sit at a comfortable 37 degrees Celsius,
but the echidna only gets up to 32 degrees and down to 10 while hibernating. Now, temperature is one variable that fits
into the metabolic theory of ecology, a mathematical model that describes how an organismās metabolic
rate relates to things like body mass and lifespan. Scientists have found that echidnas have a
relatively low basal metabolic rate, even compared to platypuses. That means they typically use energy more
slowly. Because echidnas are also relatively small
and stay cooler, the metabolic theory of ecology predicts a longer lifespan. The thing is though, by some calculations,
echidnas live almost 4 times longer than these predictions say they should. So researchers think there must be something
else going on. And itās probably related to how their cells
defend against damage. In a study from 2010, echidna skeletal muscle
and liver cells were shown to be resistant to something called lipid peroxidation. Peroxidation is a chemical process that happens
naturally to molecules in cell membranes, specifically fat molecules with double-bonded
carbons. These lipids are attacked by chemically reactive
compounds and break down in a sort of chain reaction. And we think this is one of the key parts
of aging. Now, echidnas have a lot of monounsaturated
fats in their cell membranes. And these molecules are less likely to be
broken down because they only have one double bond. This sort of resistance to aging is unusual
but not completely unique. Animals like naked mole rats and humans have
similar cell membranes and live longer lives. So the weirdest thing about echidnas is probably
comes down to their reproduction. Males flock to females, often in āmating
trainsā of 6 or more echidnas hoping to sow their wild oats. They build the females a trench and then fight,
trying to push each other out. And eventually, one pair mates. Every female actually has two reproductive
tracts branching off a single opening. And every male has a four-pronged penis. And, it turns out, only two of the penis heads
are active during one mating session. Which I guess that makes sense ā one sperm-cannon
per reproductive tract. One paper suggested that this is because of
competition. Basically, the first male who mates with a
female wants to beat out other sperm that might be deposited later. But we arenāt exactly sure why the four
prongs exist, if they only use two at a time. It might also be competition-related. They could use two different pools of sperm,
or cut down on the refractory time between mating sessions, because the other half of
their penis is ready to go. Researchers have even compared this kind of
half-activation to the the two hemipenes of lizards and snakes, which are used one at
a time. After an egg is fertilized, it grows inside
the female until itās about 2 centimeters across. Then, the soft-shelled egg gets laid into
a pouch, which is kind of similar to both modern reptiles and marsupials. After about 10 days the baby, called a puggle,
hatches. It latches on to a mammary gland on the echidnaās
belly to feed, because echidnas donāt have nipples. After about three months, it crawls out into
the world. So weāre not entirely sure how monotremes
fit into the evolutionary transitions between laying eggs and giving birth to live young. And since echidnas also have a long life and
weird digestive systems, it seems like they just sort of pulled from a grab-bag of adaptations. The journey of evolution keeps finding ways
to surprise us. Here at SciShow, we would like to take you
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than than a few weeks, we are just going to spread out showing of it to you. Squarespace is known for being user-friendly,
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of a website or domain. [ā©OUTRO ]
Echidnas are just like tortoises. Both evolved quite recently from animals that were semi-aquatic for many millions of years. Also coincidentally both live much longer than their predecessors and other similarly-sized animals and form mating trains. Echidna parental care is between that of a marsupial and an absentee-care placental parent like a rabbit.