The puzzle of the platypus: could time be up for this iconic Aussie animal?

By Science and environment editor Karen McGhee | September 5, 2019

With bizarre physiology and an equally strange collection of genes, the platypus is like no other animal. But, after more than 120 million years of evolution, could time soon be up for this unique Australian.

THE MORE WE DISCOVER about the platypus (Ornithorhynchus anatinus) the weirder it seems.

A platypus waddling through snow.

The latest feature setting this Australian species apart, yet again, from any other living animal is a unique protein in its milk that’s been found to kill bacteria and other microbes.

Scientists at Deakin University, Victoria, believe it could be an answer to deadly antibiotic-resistant bacteria, which are infecting increasing numbers of people worldwide. But that’s not all.

The platypus is one of only a few mammal species that produce venom and last year University of Adelaide-led research began exploring a hormone in this complex chemical cocktail as a potential new diabetes treatment.

Who’d have thought answers to two of the biggest human health scourges of the 21st century could be paddling about in eastern Australia’s rivers?

Ironically, however, just as the platypus seems likely to become a modern miracle for medicine, signs are that its populations have been crashing Australia-wide.

Ecologists are now asking if the species is already on the path to extinction.

Read more: Prehistoric Platypuses with bite

Platypus genetics

The platypus had western scientists scratching their heads since 1798 when a pelt was sent from the young colony of New South Wales to the natural history section of the British Museum.

With a leathery bill shaped like a bird’s, a tail like a beaver’s, webbed front feet and the trademark fur of a mammal, it was thought to have been a hoax stitched together by a fraudster.

Long after science was finally convinced the creature was real, and most likely a mammal, fresh debate and bewilderment arose when it was discovered that platypuses lay eggs, like most reptiles, with leathery shells.

Even more peculiar was what hatches from these – tiny underdeveloped foetus-like babies. This unlikely mode of reproduction is a trait the platypus shares only with the echidnas; together they’re scientifically classified as monotremes.

Monotremes are one of three main groups of living mammals. The others are: placentals, which include cats, rats, dogs and us humans; and marsupials, of kangaroo and koala fame.

The lineage that led to all three mammal groups split more than 250 million years ago from the evolutionary path that gave rise to modern reptiles and birds.

Monotremes then split from the line leading to the other mammal groups about 166 million years ago.

It was this evolution and the fact that all three mammal groups survive naturally only in Australia that, in 2001, motivated
Dr Frank Grützner to leave Germany’s prestigious Max Planck Institute and relocate Down Under to the Australian National University.

In 2004 he led an Australia–UK team that revealed yet another strange, and still largely inexplicable, feature of the platypus: it has 10 pairs of sex chromosomes.

Most mammals have just one pair. Humans, for example, have X and Y sex chromosomes with females typically having two X chromosomes while males have an XY combination. Why does a platypus need 10?

“I have no idea, and it’s really frustrating because everyone wants to know!” Frank says.

“This dazzling complexity of sex chromosomes hasn’t had any negative effects because evolution would have caused it to be weaved out. So, maybe it’s had some positive effects and there is some selective advantage we don’t yet know about.”

Frank, now a genetics professor at the University of Adelaide, was, in 2008, one of the lead researchers that decoded the platypus genome.

That proved that the crazy mix of features the platypus shows externally is certainly written in its DNA, with a blend of mammal genes and some that look much like those of reptiles and birds.

The decoded platypus genome continues to provide fodder for scientists worldwide researching vertebrate evolution. And for Frank, it has spawned new research with a potentially useful human health application.

The platypus has no stomach, possibly because it doesn’t need one because it breaks up food so efficiently by grinding it between plate-like ‘teeth’ together with river gravel.

With no stomach, the platypus, not surprisingly, doesn’t have genes for one. But it does have genes for an insulin system, which is critical in all mammals.

Insulin lowers blood sugar levels after a meal and its release is triggered by a hormone called GLP-1. This, however, breaks down in only a few minutes, not long enough to regulate blood sugar in type 2 diabetes, the most common form of diabetes.

Longer-lasting compounds that mimic what human GLP-1 does are used to treat type 2 diabetes, but they have side effects. And that’s where platypus GLP-1 comes in: its differences to the human version seem to make it last longer and function slightly differently, giving it the potential to regulate blood sugar better in diabetes patients.

“We would really like to understand how the platypus hormone works because it may lead to a better treatment for type 2 diabetes and maybe fewer side effects than what’s currently available,” Frank explains.

Strangely, the platypus gene for GLP-1 is active not only in the gut but also the venom, which scientists already know is a complex substance.

“That’s really exciting because we think this dual function has shaped [platypus GLP-1] so it’s metabolically more effective,” Frank says.

What it does in platypus venom, however, and why it’s there remains unclear.

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The wonders of platypus milk

Platypus milk SEEMS as extraordinary as the animal itself.

In just a few months, it transforms the highly underdeveloped baby platypus – jelly bean sized, furless, limbless, blind and unable to regulate its own body temperature – into a furred, smaller version of the adult, able to fend, swim and forage for itself.

“There is evidence the mother changes the milk as the young grows, so in the early stages it has different fats and proteins than at the later stages and that’s completely in parallel with how the baby is growing,” explains Deakin University geneticist Dr Julie Sharp.

This also happens in placental mammals (such as us), she agrees, but not as dramatically as in platypus milk.

Julie began studying monotreme milk more than 10 years ago, thinking its components might help premature human babies.

“If we found factors that aided development, we thought we could use them to accelerate the developmental process in preterm babies and aid their survival,” Julie says.

That outcome was never quite achieved. But now the research is being revisited with a new focus after Julie identified a microbe-killing protein in platypus milk, the structure of which was determined last year by CSIRO.

“We found numerous proteins that were completely unknown, picked two of the most abundant and they turned out to be antimicrobials,” she says.

Other mammals’ milk have antimicrobials but well below the concentration in platypus milk.

Why does the platypus need to stack its milk with so much antimicrobial activity? The answer may be in the feeding physiology of platypus mothers.

Platypuses don’t have teats. Instead, milk is produced by modified sweat glands and oozes through the mother’s skin from around where you’d expect teats to be, for the babies to lap up.

“So these antimicrobials are there because it’s a very dirty environment for the young,” Julie says.

“We now think these proteins have been critical to the survival of the platypus lineage.”

They have, it seems, been the linchpin in the species enduring largely unchanged across millions of years.

The potential to turn platypus antimicrobials into treatments for humans is, Julie says, huge.

Mischievous and inquisitive

Despite their many ‘primitive’ traits and genetic connections with reptiles, it’s the typically mammalian features of platypuses that make them so endearing.

If you’re ever lucky enough to hold one you’ll feel that strongly through its body warmth – although at 32ºC the platypus is colder than
most mammals, which have a body temperature of about 37ºC.

You’ll also notice its inquisitiveness as it tries to make sense of you by running its bill probingly across your hands and any other part of you it can reach.

For the senior platypus keeper at Healesville Sanctuary, Victoria, Dr Jessica Thomas, it’s the species’ intelligence that’s most captivating.

Since she first laid eyes on a platypus 11 years ago, she has spent most days observing and caring for these enigmatic aquatic mammals at Healesville, a native animal zoo located about 60km north-east of Melbourne’s CBD  that has kept and displayed platypuses since it opened in 1934.

It presently has eight adults, including a female aged about 25 years, and is one of only two zoos worldwide to have successfully bred the species in captivity; the other is Taronga, in Sydney.

Jessica has been particularly struck by the platypus’s ability to problem-solve.

“They can quickly work out how to get around new areas and don’t make the same mistake twice,” she says. “And they can certainly tell different keepers apart – it’s quite remarkable.”

She thinks that has something to do with their ability to sense electric impulses, “because we’re all different in that capacity”.

Platypuses are so sensitive to different people that new staff to Healesville Sanctuary’s platypus enclosure are introduced gradually over months, until the animals become familiar with them.

For Jessica’s recently completed PhD focused on platypus behaviour, she placed a camera into a nursery burrow to follow a mother and offspring from the egg stage to weaning – the longest period the process has been scientifically and visually documented like this.

Males have nothing to do with raising the young. These are animals that live in and around fresh water and both sexes shelter in dry resting burrows tunnelled into riverbanks above high water. But the female works alone to construct and maintain a nursery chamber, which she at first seals herself into after laying sometimes one, usually two, but occasionally three, eggs.

She incubates these by holding them close to her body using her tail. The extraordinarily underdeveloped babies hatch in about 10 days.

“They need to create a nursery burrow with all the right conditions to support those very young babies,” Jessica says.

“It needs to be humid, have nesting material and be between 18ºC and 20ºC.”

The mother seals her babies into the tunnel but knows how to get back in and seems to do a lot of maintenance work on it.

“I’d often track her leaving but it would be one or two hours before she’d come out at the surface.”

Even after a decade of watching platypuses closely, Jessica says it was “remarkable” to observe babies in the burrow, sleeping belly-up and forever climbing around over each other.

“Then as they got older, almost when they were about to emerge from the burrow and go into the water, they’d wander around, chew on bits of grass, and really investigate [the burrow] by pushing their bills around the edges and even up to the camera,” Jessica says.

Adult platypuses forage for up to 12 hours a day, staying under water with eyes, nostrils and ears closed for up to two and a half minutes at a time, before rising to breathe.

Mothers forgo much of this foraging time during the first weeks after their babies hatch, rarely leaving the burrow to feed, and relying on fat stored in their tails for energy.

After about four months, the young are ready to venture out of the nesting burrow. By about halfway through that period, however, they will have grown fur and their mothers will have started spending increasingly longer spans of time away looking for food to support their milk production.

“Towards the end, when the young are almost independent, it will only be every second day that she goes back and even then she’d only be in the nest for about half an hour while she feeds them and then leaves,” Jessica says.

To feed, the babies literally jump on their mother and their whole bodies appear to move as they work to force milk to ooze from her.

Milk production places an enormous burden on the mother’s body. Jessica’s research shows that by the end of the fourth month, a mother eats twice the amount of food as a non-lactating animal, which is normally up to 20 per cent of its body size anyway.

Most mammals would consume up to 10 per cent of their body weight per day but aquatic mammals need more to maintain their body temperature in water that’s usually colder than the ambient temperature.

Another feature Jessica finds remarkable about platypuses is their resilience and capacity for survival.

“They are just healthy animals that appear to have very good immune systems,” she says. “They don’t get diseases in the way a lot of other species, in particular birds, do.

“On the odd occasion they need to go to the vet it’s usually because they’ve been a little bit too mischievous, a little too inquisitive and have got into something they shouldn’t have.” Injuries, however, Jessica says, usually heal remarkably quickly.

Is this the end of an icon?

While platypuses seem to have been able to withstand whatever has been thrown at them for millions of years, research shows they’re now doing it tough.

A three-year University of NSW investigation that wrapped up last year examined records for the species for the past 200 years and compared them with extensive new field investigations on rivers in NSW and northern Victoria.

The results were alarming, prompting project leader Professor Richard Kingsford, director of the UNSW Centre for Ecosystem Science, to say, “We have great concerns about the future survival of this unique species.”

As the project began there’d only ever been two long-term studies investigating population levels, undoubtedly because surveying these animals in the wild is intensive and time consuming.

“So we really had no idea of what was going on with platypus numbers,” says one of the project’s key researchers, ecologist
Dr Gilad Bino.

As well as its intensive field surveys of platypus populations, the project collated many historic scientific and public records of platypuses occurring in numbers that would now astound most Australians, let alone scientists working on the species.

It uncovered records of people watching dozens of platypuses at a time, unlike anything reported in recent times, suggesting the species was once considerably more abundant than it is now.

“For example, there’s an account from a person on the Gwydir [River] sitting in one spot and observing at least a hundred platypuses swimming downstream, “Gilad says.

“There is no doubt of a ‘shifting baseline’ in our collective memory of what was. The world we see around us today, in terms of biodiversity, is only a fraction of what it was only a hundred years ago. I hate to imagine what will happen over the course of the next 100 years if we don’t stop destroying the world in which we live.  Our research is trying to estimate declines and find ways to conserve this amazing creature.”

The study estimates there has so far been at least a 30 per cent decline in numbers across the species’ range since European colonisation.

When Europeans first arrived on Australia’s shores, platypuses occurred in streams and rivers right along the eastern seaboard from South Australia to Queensland, and throughout Tasmania.

The species is now missing completely from parts of that range. In SA, for example, it’s thought to be close to extinction.

Josh Griffiths, senior wildlife ecologist with private Victorian research organisation CESAR, which grew out of Melbourne University, has been investigating platypuses in the wild for more than a decade. He says CESAR’s figures certainly fit with what the UNSW research has shown.

As an example, Josh points to the Wimmera region in western Victoria where platypuses were widespread and common as recently as 20 or 30 years ago.

“Now the only population there is in one small waterway. They have otherwise disappeared from the entire catchment,” Josh says.

Rivers in the area are part of the catchment for the Murray-Darling basin. Decline in river flows due to drought and water being removed for irrigation is thought to be a primary cause for the loss of platypuses in the Wimmera.

There are other rivers in Victoria and NSW where the species once occurred but is now considered to be extinct. Because most platypus research has been focused on the southern states, the situation in Queensland is largely unknown.

So what should the conservation status of the platypus be?

“That’s one of the big queries,” Josh says. “I mean, up until a couple of years ago they were classified as a ‘species of least concern’. Clearly, anyone that works with platypus[es] knows that’s not the case, but there hasn’t been the body of work done to be able to have them upgraded [to a higher threat level].”

Conservation status is a standardised ecological listing tied to a species’ extinction risk and legal protection.

The worldwide classification system for conservation status is overseen by the International Union for Conservation of Nature (IUCN), which administers the Red List of Threatened Species.

In Australia, species conservation comes nationally under the Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and in each state and territory there is locally relevant legislation.

These laws help governments guide the allocation of funds for research and protection.

If an animal isn’t on any of these lists, it’s unlikely to attract much in the way of financing for conservation. And yet the catch 22 for the platypus is that research first needs to be undertaken to reveal its true population levels.

The platypus is currently listed as ‘Near Threatened’ by the IUCN and under the EPBC Act but researchers at UNSW are currently working with the Australian government to list the platypus as ‘Vulnerable’ to strengthen protection under the Commonwealth legislation.

It is hoped the results of the UNSW project, along with research from organisations such as CESAR and the not-for-profit Australian Platypus Conservancy, will correct public and legislative perceptions that the species is secure.

“If you talk to landowners and people who have lived on properties for 40 or 50 years the common thread you get is that we used to see platypus[es] quite regularly here and we very rarely do now,” Josh says, explaining that the main threat faced by the platypus is the reduction of river flows. That’s due in part to droughts but largely because of increasing levels of water being taken from rivers for domestic, agricultural and industrial use.

A reduction in water quality is also an issue. That’s not so much because it directly affects the health of the apparently resilient platypus, which Josh has even seen thriving in sewage ponds, but because it affects the food it eats – the tiny invertebrates that need clean water to survive and thrive.

Water quality can mean chemical pollution but also physical pollution, such as increasing sediment run-off caused by erosion.

While platypus researchers are clearly worried for the species’ future, they’re optimistic we’ve caught the decline in time to respond.

“The real concern is that platypus[es] are dependent on water, and water in the next few decades is going to be the most valuable resource on the planet, if it’s not already,” Josh says.

“It’s critical for our own survival, so not many species competing for that resource are going to win that battle against humans.”

This article was published in issue 150. You can purchase your copy here.