The platypus is a fascinating animal that has perplexed generations of scientists. Now researchers are studying the platypus on the molecular level, and it’s just as surprising.

Frank Grützner is a professor of genetics at the University of Adelaide. Frank studies the monotremes, a different lineage of mammals that includes the iconic egg-laying duck-billed platypus and short-beaked echidna. 

On this episode of The Show About Science, we talk about the genetic mysteries of the platypus and their potential for advancing medical science. It’s a captivating journey into nature, genetics, and medical breakthroughs you won’t want to miss.

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Transcript:

Nate: Okay, so would you like to introduce yourself?

Sammy: Sure, my name is Sammy and I like platypi.

Nate: Okay, so you are the whole reason we are doing this episode. Thank you. But, before we start, what is the plural?

Sammy: Um, I think that the plural, it sounds better platypi. It rolls off the tongue better. It does. I’m very guilty of just saying platypuses.

Nate: ‘Cause platypuses is actually the correct plural.

Sammy: But platypi just sounds better. Like cacti, like cacti is the real plural of cactus.

Nate: Wait a minute, I think it’s cactuses.

Sammy: Really?

Nate: Hang on, I need to Google that.

Sammy: Cause I thought it was cacti.

Nate: Both are acceptable.

Sammy: Both are acceptable? I was lied to.

Nate: And then there is mongoose.

Sammy: Explain.

Nate: Mongeese, mongooses.

Sammy: Neither of those sound right. It feels like when people are debating the plural of moose. Like none of it sounds right, so they just go with moose. Look at those moose.

Nate: Mooses?

Sammy: No, like look it up.

Nate: Oh yeah, it is.

Sammy: Yeah.

Nate: Hang on.

Sammy: I’ve outsmarted you.

Nate: Yeah, you might be right.

Sammy: I’ve outsmarted the science kid.

Nate: Yeah, it is moose.

Sammy: It is moose.

Nate: But anyway, platypuses.

Sammy: Platypi, yes.

Nate: So why does this episode need to happen?

Sammy: It needs to happen because, I remember hearing about it one time on like a different podcast, but it was like a slight mention of how weird it is as an animal, and I was immediately like just obsessed with it.

And I felt like the world needed to know more about the mysterious platypuses. And you have a podcast, so…

Nate: And how did this obsession develop from there?

Sammy: Well, I started like looking things up online about them. And I was just… I was like, how does this exist? Like, they’re just very confusing, but also very interesting. And they just behave interestingly

Nate: Explain.

Sammy: They move weird to me. I’m not sure if it’s just me, but they kind of look weird when they move. But also it’s just like their anatomy, I think it’s awesome. And…

Nate: ‘Cause I mean…

Sammy: Yeah. They’re mammals, but they lay eggs, which is very confusing. Like you can see where it evolved, but it’s a mess.

It’s like if you gave a three-year-old the power to create any animal. I feel like they would create a platypus.

Frank Grützner: Yeah, and I love that idea because scientists looking at the platypus, they were astounded at how a species like that could evolve.

Nate: This is Frank Grützner.

Frank Grützner: In fact, the first specimens that were sent to England, the leading zoologists were suspicious that this was actually real.

They thought the beak was stitched basically onto some other wood or rat or something. So they thought it was in fact a hoax. And apparently there’s still scratch marks on the beaks of some of the preserved specimens at the Natural History Museum in London, where they were trying to take the beaks off.

So people that had learned a lot about zoology, they were just very confused about this animal. And that’s been ongoing with a lot of the aspects of their biology. And I think the fascinating thing is now that we look at things on the molecular level, you know, look at their genetics and their physiology, it’s just as surprising.

Nate: Okay, all right. So, let’s back up for a second. So, could you introduce yourself to the listeners, please?

Frank Grützner: So my name is Frank Grützner. I’m a professor in genetics at the University of Adelaide. I’m sure your listeners have of course already recognized that I’m an Australian citizen, but I’ve come here from Germany over 20 years ago after I’d completed my PhD at the Max Plank Institute of Molecular Genetics in Berlin.

And as an evolutionary biologist, Australia is a really amazing place because of the different species and I’ve always been fascinated studying the genetics of diverse species and I’ve worked on primates, on fish, on birds. And since coming to Australia, I’ve really got fascinated with the egg-laying platypus and echidna.

Nate: And so I’m guessing that most of our listeners here at least have heard of a platypus before. But for those who don’t know what an echidna is, what is it and how did you first learn about the species?

Frank Grützner: Yeah, so maybe if we just sort of go back a little bit. So if you look at the mammals, We can basically distinguish three main lineages of mammals.

One group of mammals that we belong to, and mice and dogs and cows, are often referred to as placental mammals. Then there is a second major lineage, which are the marsupials. There is some marsupials in South America, but mostly they’re known to be in Australia, and that’s your koalas, wombats, and of course all the kangaroos.

So these are the marsupials. And a lot of people don’t realize that there’s a third major lineage of mammals, which are the monotremes. And that’s the so-called egg-laying mammals, which sounds like a contradiction in terms, because mammals from all three lineages share that they have fur and they produce milk, but monotremes also lay eggs.

And that unique group of mammals includes the platypus and the echidna.

Nate: So are there any other species of egg-laying mammals?

Frank Grützner: So the platypus and the echidna are the two main groups. And then there’s in the echidna lineage, there’s the long-beaked echidna and then there’s the short-beaked echidna. So the long-beaked echidna is only found in Papua New Guinea.

Historically it was also in Australia, but it’s extinct. And now the long-beaked echidna is critically endangered, but it still exists in Papua New Guinea. And the short beaked echidna is in Papua New Guinea, but also found all over Australia. And then there’s the platypus and there’s really, there’s only one species of platypus.

Historically, there has been other monotremes. So there’s a giant platypus and some other species. There’s less fossil data on the echidna, but basically the surviving species on lineages include the platypuses and the echidnas, nothing else.

Nate: So what is some of the research that you’ve done or some of the field work that you’ve done, like relating to platypuses?

Frank Grützner: Yeah. So initially, what we were really interested in is to, you know, look at the fascinating biology of the platypus on the molecular level. So really look at the DNA in their cells and look how they’re organized. Now, in the case of platypus, there was something that has puzzled geneticists, which was their sex chromosome system.

Nate: Okay, before we get to the platypus, first let’s break down how sex chromosomes work in humans. So, you know that our cells contain DNA.

Frank Grützner: And that DNA is really the instruction set to build the cells that ultimately build our bodies.

Nate: And that instruction set includes a pair of sex chromosomes in each cell, one from each parent.

In most cases, biological females only have two X chromosomes, one from each of their parents. This means that their egg cells can only contain an X chromosome.

Frank Grützner: And then males have sperm cells that have either an X or a Y chromosome. And then if the X sperm fertilizes an X egg, you got XX and you get female development.

If a Y sperm fertilizes an X egg, you got XY and you get male development.

Nate: This is how it works most of the time in mammals, but the platypus is different.

Frank Grützner: Now the platypus was always a bit mysterious here because they were unclear about what their sex chromosomes are. But there was a structure when cells divide that suggested that potentially they have an incredibly complex way of organizing their sex chromosomes.

But the techniques weren’t available to investigate that further. And I was fortunate that I had learned the techniques that could solve this mystery during my PhD studies. And that technique allowed me to identify the sex chromosomes in the platypus and we were absolutely blown away because instead of having one X and one Y chromosome and two X chromosomes in females, we found five X chromosomes and five Y chromosomes in males and then five pairs of X chromosomes in females.

So that’s an incredibly complex sex chromosome system that is really unprecedented in mammals. But the other thing that we found when we looked at the individual genes, there are little bits of DNA on these sex chromosomes, we again were extremely surprised to find that they’re not the same genetic code on the X chromosomes in the platypus that’s on the X chromosome in humans, for example.

But there was DNA that was corresponding to the chromosome in chickens. So finding similarity between platypus sex chromosomes and chicken sex chromosomes was totally new.

Nate: And this discovery, well, like most discoveries, led to a lot more questions.

Frank Grützner: Yeah, so that raised some serious questions about the evolution of sex chromosomes in mammals.

And then basically six, seven years down the track, we could conclusively show by studying the platypus that there’s been two separate evolutionary events leading to two separate sex chromosome systems. And one is represented now in monotremes and the other one in mammals. What that means for humans is that our sex chromosomes are a lot younger.

it was thought the mammalian sex chromosomes evolved around 320 million years ago. By work that we did in the platypus, we could show that in fact, human sex chromosomes may be 180 million years old, so they’re a lot younger. And that shows you how studying these very different species of mammals can totally change our understanding of mammals.

Nate: So for Frank, understanding the platypus’ sex chromosome system, well, it was really just the first molecular biology puzzle to solve.

Frank Grützner: Working with the monotremes has really changed my direction. They’re so fascinating in many aspects of their biology that we ventured into other areas as well.

Nate: For example, he started studying their digestive system.

And their stomach? Well, it is totally different.

Frank Grützner: It’s been reported that they almost lack a functional stomach. There’s no acid, there’s no glands in the stomach. And then there’s the venom. So we haven’t talked about this, so the platypus is actually venomous. So they got a spur on their hind legs, and males produce a venom during breeding season.

Now venom is a very complex secretion. There’s hundreds of molecules in there, but they’re very powerful because venom usually has a really important role, either finding and killing or incapacitating your prey or defending yourself. In the platypus, the venom probably has a role during breeding season with males competing with each other.

Nate: And here’s where things start getting really cool. All of these discoveries could lead to new treatments for a disease that impacts over 37 million Americans.

Frank Grützner: Yeah, it’s an incredible story. I love to talk about it. It’s so weird and wonderful.

Nate: And that disease is diabetes.

Frank Grützner: Yeah, what happens in diabetes is generally if you have a meal, for example, I just had breakfast, I will secrete a hormone from my gut and that hormone will go into my bloodstream and it will tell certain cells in the pancreas to release insulin, which then will lower my blood sugar.

And that’s an absolutely fundamental mechanism in metabolic control, which we really use all the time without knowing about it. Now, this hormone that secreted from the gut after a meal gets broken down very quickly. So it’s maybe only active for about three minutes and then it’s gone. Now in diabetes, your body doesn’t respond to the insulin in the same way.

So that short stimulus isn’t enough to regulate your blood sugar and having high blood sugar is really bad for your health. So it’s absolutely essential for humans to operate normally to have that blood sugar regulation intact. So in diabetes, one of the main treatment options is to basically inject this hormone that’s been developed to be more stable.

So it doesn’t get inactivated that quickly. And it’s really interesting because one of the leading drugs was actually developed based on a discovery of a molecule in the Gila monster, which is a South American reptile. And it was discovered in its venom. So this hormone, which is very similar to the hormone that we use in humans, has a special function in the venom of this reptile, which is called the Gila monster.

And the fact that it’s evolved this stability has been utilized and it was discovered by John Eng in America. And then he recognized the importance and then was developed into a leading diabetes drug. So there’s a lot of interest in finding molecules, hormones that are more stable than the human hormone.

When we studied the platypus, we were interested in the stomach because we knew that they almost miss stomach. So we discussed this with colleagues and said, look, would be really interesting to look at the insulin system, you know, and this blood glucose regulation. So we looked at the genes that are responsible for, you know, these hormones and found that there’s been a single change, just basically a one letter change in the sequence of this hormone that would suggest that it’s in fact also more stable and doesn’t get degraded.

And then we were actually able to show that the platypus has in fact evolved a hormone that is more stable than the human version. And that was a very significant discovery. What’s really fascinating is that when we looked at the activity, so where is this DNA active? Where is the hormone produced? We found that it’s not only produced in the gut where you expect it, but also in the venom.

So we don’t know what the function of this hormone is in venom. Also in the Gila monster, a similar molecule is expressed or as active in the venom. So what we think happened is that this molecule that’s used normally for insulin and blood sugar regulation has evolved two functions in the platypus. One is in the gut and one is in the venom.

And its evolution in venom allowed it to establish changes that make it more stable. And there’s also some other small changes that we’re interested in. But that stability makes it interesting in the diabetes context. And we’ve received some funding to see whether it can inform treatment of metabolic diseases.

So that was a really unexpected discovery. And it’s really the start of a very long process. But I think it just illustrates that studying species that seem to be very distant, for example, from humans and peculiar in their biology, can be actually quite informative for human medicine.

Nate: Wow, that’s really amazing.

And that’s also why it’s important to remember that these animals are starting to go extinct. And we’re learning so much from platypuses and from the echidnas. And if they all disappear, what do we end up losing?

Frank Grützner: For me personally, it’s always, what are we doing to preserve these animals? I think we’re really privileged to have these animals in the Australian landscape.

And in a way, I feel like we’re the custodians of these last surviving egg-laying mammals. So really important responsibility. It’s very concerning. We’ve got pollution, we’ve got habitat destruction, and there’s actually still a lot of things that we don’t understand about these species. And so we’re constantly really trying to make sure that we do research, but also do the conservation work to make sure that we have these fascinating animals around for a long time to come.

Nate: Well, alright, thank you for being on the show.

Frank Grützner: I love it. You know, I think that’s fantastic that you’re doing this and bringing some of these fascinating species to your listeners. So thanks for your really insightful questions. It was great to talk to you.

Nate: Yeah, it was great to talk to you too. There you have it, folks.

The Show About Science is complete. Thank you so much to Sammy. This episode wouldn’t have been possible without your idea. And thank you to Frank too for being an amazing guest. Music on today’s episode was from Descript and Epidemic Sound. Our theme music, as always, was composed by Jeff Dan and Theresa Brooks.

Alright Dad, you can shut the recording off.