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Hey Short Wavers producer Burleigh McCoy in the host chair today with a biology mystery that I learned about from Catherine Wu.
She's a staff writer for The Atlantic covering science.
And a couple years ago she was talking to a scientist as part of her recent kick reporting on frogs.
As one does, and she was talking to me about hybrids.
Hybrids the result of members of two different species mating, in this case, two different species of frogs.
It just struck me as so bizarre that there would be a situation in which one frog was seeking out a mate of another species.
It made zero sense.
It had made zero sense to the researcher at the time she discovered it.
I basically had to know more.
In her reporting, Katie learned that female plains spadefoot toads that live in the North American desert actively choose to mate with males outside of their species when the pools they're in are at higher risk of drying up.
They do this because, it turns out, the tadpoles from that unlikely union mature just a little bit faster, giving them a better opportunity to hop away as adults before the pools dry up, which would be a mushy death if you're a not-quite-ripe tadpole.
But there's a catch.
The offspring are less fertile, so the males are totally sterile and the females don't produce as many eggs.
Because the fitness of hybrid animals across nature is often subpar.
A disaster most of the time.
Think of the sterile hinnies and mules that come out of horse-donkey unions.
You think of kind of sad-looking ligers that come out of lion-tiger unions and zoos.
And this was really the predominant thinking for decades and decades and decades.
That is, until recently.
There are these estimates that are probably underestimates at this point that something like 10 of animal species and 25 of plant species do regularly mate outside of their own species.
And it's not a total disaster.
It can't be.
Otherwise, that wouldn't persist over time.
Scientists are finding that sometimes hybrids can form brand new traits.
Neither of its parents could form anything that even looked like a potato, and somehow their offspring did.
Today on the show, the ingenuity of hybrids.
We move from frogs to how scientists resolve the mysterious origins of a beloved staple crop, the potato, and how this and other hybrid stories are reshaping scientists' notions of them.
You're listening to Shortwave, the science podcast from NPR.
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Okay Katie, let's start with where potatoes come from, which is from two very old distinct species of plants.
Do you know what those two plants looked like?
So I could not responsibly describe for you what two roughly 9 million old plants looked like.
But you can sort of guess because both of their descendants are around today.
So one of them was a tomato plant.
We all can kind of picture a tomato plant like nice beautiful reddish kind of fruits on a leafy green plant.
And the other one.
If you've ever seen the top half of a potato plant above ground, it looked mostly like that.
Leafy, green, some nice flowers on top.
Okay.
So these are the two parents of what resulted in the potato.
And I didn't realize that this was like a lost love story that no one really knew the answer to.
But apparently it stumped scientists for a long time.
Yeah.
And, you know, a bunch of them put it to me this way, you know, just with all due respect to potatoes, their family tree is this total and complete mess.
I can relate, actually.
I think a lot of people can.
Potatoes are messy.
Lots of family drama.
But basically, they know that there's more than 100 potato species around today.
But when they try and trace those back in time and figure out where did all of them come from, what was sort of the inciting event that spawned this massive diversity of species, they end up getting stumped.
Potato genomes are really complicated, and so they can't just piece it together really easily like they can for some other plant groups.
But they had a couple ideas.
So potatoes are within this big group called the nightshades, which actually does include the tomato.
One of its parents we now know.
This makes sense as a gardener.
Yeah, but also eggplants and peppers.
This is a very delicious, very productive family.
But they couldn't figure out exactly where potatoes had come from.
The two main candidates were actually tomato and E tuberosum, which is the other parent in the story.
But scientists were basically always considering one or the other, tomato or E. tuberosum.
For the answer to now be both is a little bit mind-blowing, because you don't expect it to be this love story that yields a hybrid that becomes the potato.
You figure, oh, it's most closely related to the tomato.
No, it's mostly related to E. tuberosum.
It was a team tomato or team E. tuberosum story.
Team both was not on the table.
Okay.
And so is it that they thought that the potato part of the plant evolved either when it was in the lineage of, like the tomato plant, or this E tuberosum, and that at some point – the one with the potato crossed and that's how like, their genes intertwined.
But they never thought that it was this hybridization event this, this coming together of two separate species, that that actually was the thing that created the what would become the potato Right.
So what was so confusing and frustrating about piecing together this origin story was, if you looked at the potato genome, parts of it looked like the tomato genome and parts of it looked like the E tuberosum genome.
And so it was like, well, okay, so which did it come from?
Was it that it evolved from a tomato plant that somewhere down the line just invented the potato?
And then maybe you mixed with E tuberosum and that's how E tuberosum stuff got in the potato genome.
Or was it the total inverse?
Those are really the two main possibilities that people were considering.
They didn't find that.
All the species they looked at had roughly the same mix of tomato and E. tuberosum as each other.
Like they all looked like the same medley, which means that there was probably just one event that brought the tomato and E2 erosome genomes together, which means hybridization.
That's kind of the only option when you see the data that they saw.
So there was one event the two genomes mixed and that spawned, you know, an early potato, and that early potato led to the hundred plus species we see today.
It wasn't that a tomato made a potato and then weird stuff happened later on.
It was that these two plants came together initially and the potato was born, and no one ever looked back.
And so this big surprise, this hybridization event led to what we know and love as the potato.
I suspect we also don't really know much about what that looked like, but I want to ask just for fun what do you think it looked like?
Like a tomato bit in the ground?
So I have no idea what the first potato plant looked like, but it probably was not a tomato growing underground.
Okay, okay.
Just like, given the way that plants produce different organs, like tomatoes come out of the flowering parts of the plant right.
And so that is above ground.
When we're talking about a potato, that is like by definition an underground storage organ.
It's a tuber, right?
It has to kind of come out of like the underground system where a bunch of nutrients are being stored.
I mean, a potato is basically a giant nutrient stored organ.
And so you're never going to get a potato.
You're never going to get a proper potato growing on the above ground portion of a plant.
And you're never going to get a proper tomato growing on the below ground portion of a plant.
Can uncovering this potato mystery help us with the spuds of today?
Like it seems like really interesting science, but can it inform how we're growing food now?
I think the answer for right now is maybe question mark, probably question mark.
There is not a set in stone plan to fix everything that is wrong with potatoes today.
But potatoes, you know, the potatoes we eat, they do have issues.
They are susceptible to disease and their genomes are kind of a pain to work with.
So cultivated potatoes, the potatoes we eat, they have four copies of every chromosome.
And that's a real pain for breeders.
Just trust me on this one.
It is a huge pain for breeders.
And so if they can figure out a way to just use this information to improve the potato genome and make it easier to work with, maybe that could be really interesting.
One sort of out-of-the-box idea that some of the scientists who worked on this project are playing with are using this information to help tomato plants make underground tubers, so making their own potatoes.
What?
They don't know if this is entirely possible, and it will probably be extremely difficult, if it is possible at all.
But you know, it could be the case that someday you're eating fries and ketchup and they came from essentially the same plant.
My gosh, that would be so amazing.
I will say scientists have kind of cheated their way to that solution before.
You know, the tomato and potato plants are still closely related enough that you can graft them onto each other.
So you can, you know, it's like a Franken plant, right?
You can mash them together and they stay alive and produce both things?
Yeah.
It's not quite the same as coaxing a tomato with genetic manipulation to make its own potatoes, but it's a little bit more like organ donation when you slice the two together.
Or human centipede, whichever metaphor you prefer.
One is a little grosser than the other.
Yes.
I need one of these plants now.
So this example of a hybrid and, like the frogs that we talked about earlier, what do they tell scientists about how useful hybrids are?
I think these examples, and a bunch of others that have emerged in recent decades, are really helping to rewrite the evolutionary story on hybrids.
It is still absolutely the case that most of the time when a species mates with another organism outside its own species, it's not going to work.
They probably won't have successful offspring to begin with.
But sometimes it does work.
Sometimes those offspring do come to be.
Sometimes those offspring can reproduce.
And sometimes those offspring are so different, in interesting and exciting ways, from their parents that they're able to do things that neither of their parents could.
And that can lead to really incredible events like making lots of new species striking out into new environments, even potentially human evolution.
It, So it can be a really powerful evolutionary force that can drive evolutionary innovation in a way that just mating within your own species can't.
Catherine Wu is a science journalist at The Atlantic.
See our show notes for both of her articles on the hybrids.
Thank you so much, Katie.
Always good to be here.
This episode was produced by me, Burleigh McCoy, and edited by our showrunner, Rebecca Ramirez.
Tyler Jones checked the facts and Robert Rodriguez was the audio engineer.
Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy.
I'm Burleigh McCoy.
Thanks for listening to Shortwave from NPR.
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