The Genetic Mystery Of The Invasive Crayfish Clones

9:06 minutes

a gray speckled crayfish with eggs beneath tail
A female marble crayfish with her young tucked under her tail. Credit: Shutterstock

Sometimes, when pet owners get tired of taking care of their carnival goldfish or their python becomes too much to handle, the pets are released back into the wild. Scientists have warned against this because these animals can lead to unforeseen consequences in their unnatural habitats.

The marbled crayfish is one such former pet. This all-female crayfish species originated from a hobbyist tank in Germany 25 years ago. In the wild, the crustacean developed a mutation that allowed it to pick up a third set of chromosomes and reproduce clonally. Since then, the cloning crayfish have proliferated—invading waters all around the world.

[Is the “rise of slime” upon us?]

A group of researchers sequenced the genome of the marbled crayfish to investigate how this mutation may have occurred and what effects it has had physiologically and genetically on the species. The results were published this week in a study in the journal Nature Ecology and Evolution. Neurophysiologist Wolfgang Stein, an author on that study, discusses the findings and what the neurons of this clonal creature might tell us about its ability to adapt to different environments.

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Segment Guests

Wolfgang Stein

Wolfgang Stein is an associate professor of Neurophysiology at Illinois State University in Normal, Illinois.

Segment Transcript

IRA FLATOW: You know the story of the Teenage Mutant Ninja Turtles, those little pet turtles who, after stepping into a mysterious radioactive goo, became New York City crime fighters? Well, there is a real life version of that, an army of mutant female marbled crayfish. I’m not making this up.

They are taking over the waters across the world. Now we can’t confirm if these crayfish are fighting crime or teenagers, but they did arise from a strange aquarium accident where they were released into the wild. Scientists are baffled by how this has all happened. I see a movie here.

A group of researchers sequenced the gene of the marbled crayfish to try to get a better understanding. And their findings were published this week in the journal Nature Ecology And Evolution. And my guest is one of the authors on that study, Wolfgang Stein, professor of neurophysiology, Illinois State University in Normal, and crayfish genome researcher. Welcome to Science Friday.

WOLFGANG STEIN: Hi. Thank you very much for having me. What a great show so far.

IRA FLATOW: Thank you. Well, you’re part of it. And you have a great story to tell. Give us a little background, the origin of how the species of crayfish came to be.

WOLFGANG STEIN: Yeah, it’s actually quite interesting. Like you said, we sequenced the genome of this puzzling the genetic species, the marbled crayfish. And they reproduce asexually, basically. We don’t really know exactly how it happened. But at the time, two slow crayfish– those are crayfish that lived in Georgia and Florida– a couple of them mated, and something went wrong.

And one of the daughters of these animals inherited an additional set of chromosomes. And that daughter then could no longer reproduce normally, but instead was able to generate live offspring without any males. And this is quite interesting because that happened like 25, 30 years ago. So it’s really only species where we can actually account for when the species started. So this is a new species that really has only been in existence for like 30 years or so.

IRA FLATOW: And in those 30 years, it has been multiplying around the world?

WOLFGANG STEIN: Yes, it’s crazy because we’ve been able to track those animals back to one animal. And so all the crayfish that we have in existence now of that species stem from that one accident, that one animal that inherited those additional sets of chromosomes. And so by now, they have spread all over the planet.

We find stable populations in Japan, in Europe, in many countries, in Madagascar. And you can buy them in the US as well in pet trade. There are no stable populations in the wild so far. But actually, I wouldn’t be surprised to find them.

IRA FLATOW: So they’re not living in the water? They’re living in people’s aquariums?

WOLFGANG STEIN: They are living in people’s aquariums, or wherever you put them. And that’s actually how they travel, with pet trade. And people, you get one of these animals, and they reproduce within, like, three months. You have 200 offsprings. And people get tired of them. And the worst thing that they can do is they put them in the lake next to their house. And a year later, you have thousands of these animals.

IRA FLATOW: In the lake?

WOLFGANG STEIN: In the lake. Yes.

IRA FLATOW: Did they start attacking things in the lake?

WOLFGANG STEIN: Not that we are aware of. But they are out-competing the local crayfish species. And so eventually, this will be a problem for conservation of the local species. And they spread really, really fast. And this was part of the study as well.

In Madagascar, we tracked essentially since 2007 how much they spread. And just to give you an idea, when they were first discovered in Madagascar in 2007, they occupied a space of, like, half the size of Rhode Island. And by 2017, that’s the size of Ohio now.

IRA FLATOW: Wow. I’m just trying to soak that in.

WOLFGANG STEIN: It’s about 100-fold increase in area that they live in 10 years.

IRA FLATOW: How do you know if you have one?

WOLFGANG STEIN: Well, the easy way is actually you take it, you put it in a tank, and you wait a couple of months, and you’ll have offspring. If there’s no other animal in there, you can be sure that you have one. They have a certain, when you look at them, the coloring. That’s why it’s called marbled crayfish. So that said, they are not very easy to differentiate from other species out there.


Yeah, go ahead. Go.

IRA FLATOW: No, no. I’m just soaking this in. And I know there’s something called parthenogenesis, where animals reproduce asexually.


IRA FLATOW: Is this what’s going on here?

WOLFGANG STEIN: Yes. That’s exactly what’s going on. The parthenogenesis, like you said, is just an expression for asexual reproduction. And there are other species that do that. So the interesting thing about this particular species is that we can now track it as this happens. We know, 30 years ago, this species came about.

And now we can track how the genome of this animal actually changes, because for most of the species that reproduce asexually, we know they are genetically diverse. This hasn’t happened to these animals yet. So we are a bit baffled by this, actually.

IRA FLATOW: I can tell. I know you call your lab The Crab Lab.


IRA FLATOW: Where you study all sorts of crustaceans. But you’re a neurophysiologist. What are you trying to learn about this? Let me just let you answer this as I give the ID. This is Science Friday from PRI, Public Radio International.

WOLFGANG STEIN: So I’m a neuroscientist, as you say. And my interest is in how drugs and medications affect the brain. And so it’s well known that people respond quite differently to medication. But it’s really not clear why it is the case. And so the underlying assumption is always that this is differences in genetics.

And we now have the chance to test this, because the genetics in these animals is really the same. It’s identical. And so we can test how diverse the brain actually is if you are genetically identical.

IRA FLATOW: Now I know you have you might have marbled crayfish in your lab. Do you keep them under lock and key? I mean, how do you?

WOLFGANG STEIN: Yes, we indeed do. We make sure that they don’t get out. We don’t want to cause an infestation in the local lakes here. So yes, we have separate tanks that we pay well attention to. I guess.

IRA FLATOW: I am thinking of movies from the 1950s, now where somebody from Hollywood is going to call you any minute.

WOLFGANG STEIN: You know, they’re a good source of protein. So I guess one way of getting rid of them would be to eat them. So that would be a way.

IRA FLATOW: How do they taste? I know you must have tried them.

WOLFGANG STEIN: No, I have not tried them. I have tried to crabs that we worked with, but I have not tried the crayfish. But I suppose they would taste similar to other crayfish.

IRA FLATOW: Some people call them crawfish, in different parts.

WOLFGANG STEIN: Yes, Southern parts usually I guess.

IRA FLATOW: This is, to me– so what have you learned about their neurology? And their physiology, are they different from other crustaceans or crawfish?

WOLFGANG STEIN: They are, in terms of the neurons that they have, very similar to other crustaceans, in particular, the two crabs and other crayfish. What we’ve seen so far is that they’re really less diverse. So if you go from one animal to the next animal, it seems like they are more identical, which corresponds to the ideas that we have. And so theoretically, they should be more susceptible to interference. Like if I give them a certain drug or so, they should respond all the same.

IRA FLATOW: You know, I was an old aquarist myself, I used to have a lot of fish tanks. You know, the aquarist of me says I’m going to go out and get one of these, and put it in the tank.

WOLFGANG STEIN: Yeah. You know in some areas of the world they are banned now from pet trade. In most parts of Europe they are banned. In some states in the US they are banned. I think in Illinois you can still buy them I don’t know about New York.

IRA FLATOW: But you’re not encouraging anybody to do this.

WOLFGANG STEIN: No, I would not do that. If you do that, make sure that they are not getting out. Don’t flush them down your toilet. Don’t put them in the lake next door. It would really be a problem for conservation. But there’s another part to this that kind of fits also the theme of today’s show, which is our collaborators in Germany, at the German Cancer Research Center.

They are interested in tracking tumors in that population, because for the same reasons actually that we work with these animals. Because if they are all clones, we can understand. That opens a lot of doors to understanding how tumors come around in a population, and spread out across populations.

IRA FLATOW: What a great idea.

WOLFGANG STEIN: Yeah. It’s really a neat species to work with, and we’re all excited to have it.

IRA FLATOW: So nature did this accidentally, and now you can make use of it.

WOLFGANG STEIN: Yes, actually since you mentioned it nature did this. We are not sure whether it happened in a tank, in someone’s aquarium at home, or what had happened in the wild. We do know that the father and a mother were not closely related. So they might have come from different lakes or so.

IRA FLATOW: We don’t know if any radioactivity was involved.

WOLFGANG STEIN: I highly doubt it.

IRA FLATOW: All right, Dr. Stein. This is quite fascinating. Don’t go out and get the crayfish.


IRA FLATOW: Wolfgang Stein, professor of neurophysiology in Illinois State University. Thank you for a very informative discussion.

WOLFGANG STEIN: Thank you very much.

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