Marsupials evolved in Australia's isolated continent through natural selection, developing unique survival adaptations such as the red kangaroo's efficient hopping locomotion (storing energy in tendons like coiled springs), specialized water conservation mechanisms, and a sophisticated reproductive strategy where females can carry a pouch joey while simultaneously caring for an older joey and maintaining an embryo in suspended animation (diapause) until triggered by the older joey's growth.
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The Australian Outback, Land Of Extremes! | Ep 2 | Life Force S1追加:
Our miracle planet is ever changing.
Over vast time scales, continents travel and climates swing, forcing all creatures to find original ways to survive.
This is a journey to understand one force that shapes all life.
Evolution, the life force of our planet.
The land of heat, fire, and venom.
A dry, Mars-like continent with toxic soils.
Yet animals have mutated and evolved to flourish here.
Improbable monsters, dragons, dinosaurs, and devils.
Families of bizarre pouched mammals dominate every habitat on this ancient continent.
Where did they come from?
What forces shape them?
How do they survive in this land of mutants?
Ancient Australia, an isolated floating laboratory where the original inhabitants have been trapped for millions of years.
As they multiplied, [music] they mutated.
Each genetic variation shaped and tested by the extreme environment.
Only the mutations that offered advantage survived and were passed on until the continent became dominated by weird creatures found nowhere else on the planet.
Desert covers more than half of Australia.
In the height of summer, it's one of the hottest places on Earth.
Over 46° C.
Reptiles thrive here.
The thorny devil lizard, coated in camouflaging spines, is able to survive with minimal moisture.
And the giant perentie lizard, a ruthless predator and scavenger.
But what mammal could survive out here?
The red kangaroo.
The males are the color of the desert.
Up to 1.8 m tall and weighing up to 90 kg.
The females, at around 35 kg, are colored all shades of gray.
The hero of this story is an adult female, mother to a 10-month-old called a joey.
>> This is the family unit.
The male plays no part in rearing the young.
So, the female must ensure the survival of each generation.
She dedicates her life to her offspring.
Kangaroos belong to a major group of mammals known as marsupials, commonly defined by the females rearing their young in pouches.
In the desert, this marsupial mom still provides milk for her female Joey, despite not having drunk any water for 5 days, long enough to kill a human.
But, marsupials are mutant survivors.
Evolution has equipped all 156 of Australia's living marsupial species with a range of secret weapons, some shared, some unique, which enable them to exploit every habitat.
In Tasmanian mountain marsupial carnivore.
In a pouch underneath her stomach, this Tasmanian she-devil stows two babies, about 8 weeks old.
Even at this age, the little devils live up to their name.
A female devil can carry up to six babies in this pouch for 3 months.
Quite a cargo for a busy working mom.
But an ingenious way to transport vulnerable offspring.
Her powerful sense of smell leads this scavenger to a decaying wallaby carcass.
>> [screaming] >> With a chilling screams, determine dominance.
And the strongest jaws on the planet, relative to body size, carry out the devil's work.
>> [groaning and screaming] >> Five devils can strip clean a good-sized carcass in less than 1 hour.
In eucalyptus forests, live the tree-dwelling koala, which spends its life chomping eucalyptus leaves, which happen to be toxic.
The koala's digestive system is adapted to detoxify this abundant food source.
But it takes a lot of energy, as does rearing their offspring.
Brains burn a lot of energy.
>> [music] >> So, the koala's trade-off is a small brain, the size of a tomato.
Weirdly, this gives koalas an evolutionary advantage, freeing up more energy for climbing, rearing offspring, and eating more toxic leaves.
Their cousins, the wombats, dig deep burrows underground.
To protect them from predators, they've evolved a shield of impenetrable skin to guard against rear attack.
There's even a marsupial that can fly.
Like bats, sugar gliders have grown a membrane so they can glide from tree to tree.
But it's the desert dwellers that face the biggest challenge.
The water holes have dried up.
So the first of the red kangaroo's survival skills kicks in.
She's almost stopped urinating and her kidneys recycle urea, helping her stay alive and continue to produce milk.
The red kangaroo has a range of astonishing survival adaptations.
Like all her marsupial family, these evolutionary changes reach back through the geological history of the Australian continent.
A story which begins in the most unlikely place, well before Australia ever existed.
125 million years ago, northeastern China was joined to North America in a vast continental block named Laurasia.
A fossil skeleton from this time provides our only clue to the original ancestor of all marsupials.
Its name, Sinodelphys szalayi.
It measured 15 cm long and weighed about 28 g, like a tiny mouse.
The first marsupial was a climber and most likely spent its days scampering across low branches of bushes, feeding on insects.
The next oldest marsupial fossil was found in what is now Utah in the United States.
Dated around 110 million years ago.
So, it appears that marsupials dispersed south from North America, most likely via a small arc of volcanic islands.
During this marathon journey, the tiny mouse-like Sinodelphys mutated into variations of the original marsupial.
And these species spread into what remained of the ancient continent, Gondwana.
Gondwana began breaking up 130 million years ago and finally, Australia ruptured from Antarctica and formed a new continent, trapping many of the new species of marsupials.
There may have been other types of mammals as well, but what happened to them remains a mystery.
What we do know is that the age of marsupials had begun.
Today's red kangaroo is millions of genetic mutations away from its Chinese ancestor.
But even these mutations may not fully prepare it for the merciless desert.
With the water holes dried up, the kangaroo family faces its greatest challenge.
What sort of evolutionary adaptations could possibly save them in this death zone?
In the desert, the locals abandon the dry water hole.
And the red female kangaroo knows she must move on.
>> [snorts] >> The desert grasses and salt bush she eats have grown scarce. And despite her tolerance to extreme dehydration, she must find water soon.
Especially for her vulnerable joey's sake.
The giant perentie lizard is just one threat to a youngster weakened from hunger.
And the most dangerous snake on the planet, the western taipan, patrols this arid landscape armed with enough venom to kill an animal 10 times the kangaroo's size.
But the biggest danger to all the desert dwellers is the habitat they live in.
Central Australia has officially been in drought for a decade.
Even desert kangaroos require water at least once every 10 days.
Without it, the Joey will die.
And then so will the adult.
They wait for the cooler air at dusk to begin their journey.
Now it's time for them to utilize one of their most spectacularly honed adaptations.
The hop.
Their lives depend on this unique form of locomotion.
Let me just see if I can get this girl.
Hang on.
Dr. Adam Munn is an internationally renowned kangaroo zoologist.
That's it. Yep. Yep.
Good day speed.
Passionate about kangaroos, he's investigated every aspect of their specialized survival kit in his field work.
I've been studying kangaroos for a few years. We're now out here trying to understand how these animals are surviving with the drought conditions.
Using a super slow motion camera, Oh, nice little hop.
Dr. Munn analyzes their most conspicuous survival skill.
One of the really important features of red kangaroos' ability to survive is their efficient form of locomotion, which is hopping.
All right, HOW FAST WE GOING NOW?
AN ADULT RED CAN AVERAGE around 24 km/h, and Adam has clocked them at nearly 50 km/h.
That's quick. That's a good pace.
When they hop, they hop with their their hind legs very close together and it's almost as if they hit the ground with with one foot.
They're much more efficient at traveling long distances and at higher speeds compared with a quadrupedal placental.
That was perfect.
All right, mate. Scientific analysis confirms that at cruising speed hopping is much more efficient than a horse cantering or a greyhound running because of how kangaroos store and reuse energy in each bound.
Look at that tail.
That's just fantastic.
Each hop begins off the toes.
The massive calf muscles tense.
And the long Achilles tendon stretches to capacity.
It's like hopping on a pair of coiled springs.
The tendons store the power of each hop and release it on the next.
The powerful tail also stores energy and acts as a balance.
This form of locomotion is unique to one group of marsupials known as macropods, meaning big foot.
And all branches of their family tree evolved from the ancient ancestor found in China, Sinodelphys, who didn't hop.
So, where and when did the hop begin?
Northern Queensland on the east coast of Australia, and in pockets of ancient tropical rainforest, lives a clue to solving this mystery.
The DNA of this little musky rat kangaroo dates back 45 million years.
And he's a living example of how kangaroos may have begun hopping.
His ancestors were the first macropods, and he has the big feet to prove it.
But instead of hopping, he is a quadrupedal bounder.
Despite the fact that musky rat kangaroos don't hop, Dr. Adam Munn believes they demonstrate how this evolutionary leap may have come about.
What you do see them do when they're feeding around on the forest floor, is they'll often sit up on their hind legs, and they'll look around, and they'll have a look to see where the next patch of food is. As these animals started to get bigger, you can really see in that process, in the anatomy and how the animal moves, it really probably was the the beginnings of the first hop that you see in the big kangaroos.
Hopping may have started in small forest-dwelling marsupials.
But Australia was about to enter a dramatic new phase that would drive the hop's evolution by leaps and bounds.
45 million years ago, the whole continent was green.
Large rivers flowed through lush vegetation.
The perfect environment for a dinosaur-like crocodile.
It may have hunted ancient macropods along the riverbanks of his kingdom.
Although they would have been mere snacks for him.
But green Australia wouldn't last.
The new continent was still drifting north after the great separation from Gondwana.
While in the south, cold ocean currents began flowing freely around the newly formed Antarctica, cooling it.
And slowly it froze, trapping moisture in the ice.
As Australia moved towards the equator, the continent began to dry out.
As the climate changed, Australia's tropical forests transformed into open grasslands.
And the marsupials had to adapt or perish.
The musky rat kangaroo stuck to the dwindling rainforest habitat.
>> [crying] >> But his cousins began branching out, evolving new abilities as they went.
It's likely this climate change drove the macropods transition from four-legged forest bounders to two-legged hoppers.
7 million years ago, small kangaroos called wallabies branched out in several directions.
Some species took to rocky bluffs where their feet modified, enabling them to grip rocks.
The bizarre tree kangaroo probably tried hopping on the new grasslands but returned to the forests and became a climber to reach vegetation high in the rainforest canopy.
They developed slip-proof pads on their feet and long claws.
And tree climbing required their back legs to work independently.
5 million years ago, the gray kangaroo family appeared and eventually became herd-like grazers on the grasslands like antelope on the African savanna.
They developed complex hierarchies which required behaviors to reinforce the chain of dominance.
As it grew hotter and drier the most recent macropod appeared.
Just 1 million years ago the red kangaroo claimed the desert.
Today, it's the largest marsupial on the planet.
A culmination of unique genetic mutations allowing it to survive in a death zone.
But even this mutant hero could fall victim to the extremes of a 10-year drought and the predators of the desert.
It's morning in the desert and 8 days since [music] the kangaroo and her Joey last drank water.
As the day heats up, they have to rest.
Despite her moisture [music] saving adaptations, the mother must find water in the next two days or she'll run out of milk to feed her youngster.
But for now, she still has some milk.
Over the last two months, the youngster has grown too big to fit in the pouch.
And her mother won't let her try because there's someone else sheltering in there.
The adult female has another baby, almost hairless, just 12 weeks old.
The breeding strategy of female red kangaroos is a masterpiece of mothering.
Eight weeks ago, the mother refused entry to her oldest Joey, the little female, from full-time residency in the pouch.
The adult female then began to lick the inside of her pouch.
And then, sat down on her tail, signaling the start of something special.
The birth of a new Joey.
All marsupials enter the world this way.
A tiny, underdeveloped, blind newborn.
[music] In still navigates unaided from its mother's birth canal to the safety of her pouch.
As the newborn male latches tightly to the teat to which he'll stay attached for the next few months, his mother produces a hormone that invites another large, powerful male to mate with her.
In her 12 to 15-year lifespan, a female red kangaroo can always carry a pouched youngster while also caring for an older Joey.
This super mom has evolved an ingenious way to feed both hungry mouths.
She has four teats in her pouch, two short, spare ones and two long in use.
This unique lactation system is the most sophisticated of any mammal, providing different milk to each Joey.
Her youngest baby requires high carbohydrate, low-fat milk, while the older Joey's teat provides low-carb, high-fat milk to supplement the grasses she is learning to eat.
This remarkable reproductive cycle ensures the best chance of survival for the desert-dwelling kangaroo.
But the ancient continent of Australia is a mosaic of challenging habitats for all its mutant survivors.
Since Australia separated from Gondwana, it had few earthquakes or volcanic eruptions.
So, it became the flattest of all continents.
Iconic Uluru in Central Australia is constructed of sediments from an ancient mountain range weathered over millions of years.
No geological activity means little new soil is created.
And erosion leaches nutrients from the soil that's here.
Southwest Australia and the soil is virtually sand.
But life here has adapted in exquisite and surprising ways.
Wildflowers seem to defy the barren soils they grow in.
But they need to be as flamboyant as possible to attract pollinators in this inhospitable home.
And who might those pollinators be?
Reproductive biologist Professor Marilyn Renfree specializes in marsupials.
That should be enough.
Over the last 30 years, she's dug hundreds of holes in this remote corner of southwestern Australia.
Yeah, that's perfect.
A somewhat bizarre activity for a biologist.
The morning will reveal all.
They're just the most beautiful little things.
The holes are pitfall traps. Come here, darling. So, Professor Renfree can study the bizarre reproductive strategies of these tiny marsupials.
And she's got babies.
The young are just getting fur.
This is a honey possum.
The sole survivor of a long-extinct group of marsupials.
How did they out survive other members of their family?
Every aspect [music] of these unique marsupials' lives holds a clue to how they did it.
First, their diet. Well, they're one of the few totally nectarivorous animals in the world. They feed on the nectar and pollen of these banksia flowers.
Honey possums coexist with the prevalent plant in their environment.
In exchange for food, some banksias rely on them for pollination as they scamper from bush to bush.
Their size is the next clue.
Honey possums are amongst the smallest of all marsupials.
The females [music] give birth to the smallest mammal at birth of any mammal in the world, less than 5 mg.
Can you imagine the whole of mammalian organization in less than 5 mg? It's incredible.
A 5-mg mammal is about [music] the size of a pinhead.
Being small is the best size for a nectar eater.
But, it doesn't mean they don't eat much.
When she's providing milk for her young, this little female can consume 10% of her body weight in one night, gorging herself on pollen and nectar.
With these specialized mouth parts, long, thin, rod-like jaws with virtually no teeth, but a specialized tongue with a brush-like tip and combs guaranteed to collect as much pollen as possible.
But it's the male honey possum that provides the most bizarre clues to the species' success in this arid environment.
They have the biggest testicles relative to body size of any male on the planet.
It's like a man walking around with two very large watermelons. Need a wheelbarrow to move around if you were a human with testes the same size as a honey possum.
And what's inside them is even more impressive. The sperm are the largest in the mammal kingdom at 360 microns, almost three times bigger than a human sperm, and way bigger than the sperm of a blue whale.
In the evolutionary sperm race, size really matters.
They are a multi-male mating society, [music] so if a female is in estrus, many males will mate with her.
And the larger the sperm, the hypothesis is the better that that male will be able to compete with the other males, and if his sperm is bigger and faster and better, it'll reach the egg first.
Over millions of years, those males with the biggest sperm and testicles fathered the most offspring, passing on this advantage in every generation.
But in the competition for bizarre breeding strategies, one of the honey possum's cousins comes a close second.
Unlike the honey eater, the tiny antechinus is a carnivore.
And his extraordinary life cycle enables him to populate every habitat around Australia.
For the first 10 months of his 11-month lifespan, all this male does is eat and grow.
He needs all the energy he can store because in his last month, he has a job to do that will kill him.
Every spring, and the kiness males become obsessed with mating.
They don't eat.
They don't sleep.
They just seek out females and mate 24/7.
After 2 weeks of this testosterone-fueled rampage, all the males die in a blaze of glory.
It seems and the kiness males are disposable.
A strategy that may have evolved to prevent males from competing with their many offspring for food.
In the genetic lottery, the and the kiness and honey possums bizarre breeding specializations help them stay alive while other marsupials went extinct.
This is survival of the fittest.
But in the deserts, the red female kangaroo's special adaptations may no longer be enough to save her and her offspring from the relentless heat.
11 days with no water, and the kangaroo family finds itself in dire straits.
The female can no longer produce enough milk [music] to feed both her offspring.
The older Joey is especially at risk and soon sacrifices may have to be made.
Meanwhile, both kangaroos have another strategy to help them cool down.
They lick their forearms.
Under the skin on their forearms lies a dense network of blood vessels.
Her wet saliva helps to cool the blood, which is then pumped around the rest of her overheated body.
A potential predator announces its presence.
It's enough to drive the exhausted kangaroos from their resting place.
Back into the relentless heat.
It's Australia's wild dog, the dingo.
She calculates whether she'd have a chance.
In broad daylight in this extreme heat, a successful hunt is unlikely.
But this moment is symbolic.
Each represents one of the major branches of evolution.
Both mammals, but with very different reproductive strategies.
The dingo has a litter of pups about the same age as the kangaroo's infant Joey.
But the profound difference is that she hasn't given birth to them yet.
They are still in her womb.
The dingo female nurtures her pups through an umbilicus connected to a placenta, which supplies nutrients from the mother and filters out waste.
At first, the kangaroo fetus, like all marsupials, also draws nutrients from a placenta.
But then the similarity ends.
The marsupial is born early, before it's fully developed, and makes its instinctive journey to the pouch.
There it trades the umbilicus for the teat and continues to grow.
While the dingo pups develop within their mother's womb for around 9 weeks, until they are born fully formed.
Two completely different strategies, both successful.
An ancient mutation may have caused the division, providing an advantage [music] that's been passed down.
But which came first is one of the great unsolved biological mysteries.
The kangaroo family arrives at yet another dried-up water hole alongside others desperate for water.
Some struggle to muster the energy to leave while others gave up.
The female can no longer feed her older Joey.
The exhausted youngster struggles to get some sustenance from the dried vegetation.
But without water or milk from her mother, she has little time left.
Her mother knows what she has to do.
Too weak to follow, the Joey is completely vulnerable in this merciless landscape.
The giant perentie lizard can taste imminent death on its forked tongue.
So begins to track the scent.
Desert reptiles have evolved their own strategies for survival during drought.
The thorny devil lizard always finds plenty to eat as he snaps up over a thousand ants in a day.
Rodents stay cool underground in the desert, but they share this haven with their predators, venomous snakes.
The Australian taipan has a super toxin powerful enough to kill any animal instantly.
The taipan's super venom may have evolved to enable it to kill on the spot and avoid wasting energy wrestling its prey.
Useful in the desert.
After 11 days with no water, the little female Joey has succumbed to the drought.
Her death will sustain the giant perentie lizard for weeks.
Despite kangaroo's sophisticated survival adaptations, 80% of Joeys don't make it past 2 years.
The adult female's burden is lightened at heartbreaking cost.
But she still has her infant Joey safely in her pouch.
Though dangerously stressed, she has one more evolutionary trick that will ensure the survival of her species.
The red kangaroo travels in the cool of night as her kind of evolved to do since the continent began heating up so many million years ago.
In the 21st century, Australia continues [music] to heat up.
Always unpredictable, rain is becoming less and less frequent.
Each drought lasting longer than the one before.
And the catalyst is a cycle of events triggered far from the arid center of Australia.
A thermal image shows how approximately every 5 years the water temperature of the Pacific Ocean rises.
This phenomenon is known as El Niño and has always been blamed for Australia's droughts.
But a recent discovery shows that Australia's droughts coincide with two cycles of water temperature changes in the Indian Ocean.
One extreme generates winds that pick up moisture and carry rain across the continent.
The other weakens the winds, significantly reducing rain.
It seems the cycle has remained in the weakening phase since 1992.
The worst drought since records began.
This is the reality Australia's marsupials must face.
And they have evolved strategies to survive extreme heat and the fire that drought brings.
But even 1 million years of mutations aren't enough to allow this red kangaroo to survive endless days without water.
Just as he reaches the limit of his reserves, a freak cloud of moist air from the coast gets pushed by [music] wind into central Australia, where it meets the desert heat, culminating in a thunderstorm.
It's a long time since this earth has felt moisture.
Rain finally falls on Australia's iconic [music] red center, an extremely rare event.
The violent desert thunderstorm fleetingly embraces Uluru with cascades and rivulets.
By morning, the desert is transformed.
Numerous water holes create a network of oases.
>> [music] >> The birds arrive first.
Huge flocks of corellas.
The wedge-tailed eagle.
Zebra finches.
Galahs.
The thorny devil stands in a puddle, his capillaries drawing moisture up his scaly body towards his mouth.
He's using his body as a drinking straw.
Finally, the dehydrated female kangaroo reaches life-saving water.
Alongside other desert nomads, she can finally relax.
But is it too late for her infant Joey?
Somehow, this extraordinary mother has continued producing milk and protected him from harm.
The storm was no drought breaker, but it delivered enough rain to restore the kangaroo family's strength.
3 months later finds the young male robust and playful.
But another miracle has been hidden inside his mother during her long journey.
Remember that last mating, the day her tiny baby was born, just before she set off to find water?
All along, through the trials of her journey, the female red kangaroo carried another embryo in her womb.
In a state of suspended animation called diapause, it wasn't growing, but it was alive, waiting for a signal.
Amazingly, the puppet master controlling its development is not the mother.
It's the sibling in the pouch.
While he continues to suck regularly on his teat, the unborn brother or sister remains in suspended animation.
When he ceases suckling and outgrows the pouch, this triggers the fertilized cells to grow into an embryo.
Just 30 days after conception, the newborn will make the journey to the pouch.
And the cycle will begin all over again.
In a masterpiece of mothering, female red kangaroos can support offspring at three different stages.
This extraordinary reproductive strategy, enabled by her pouch, transported by her hop, is as good as it gets at this place in time.
But evolution never ends.
With Australia's droughts growing more frequent and extreme, this remarkable survivor must keep evolving so she can continue journey on this our mutant's planet.
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