Solved: The Potato Origin Mystery

Usually, when two different species mate, it’s a disaster. At least, that’s what scientists had generally thought about hybrids, the offspring of these unions. But some researchers are starting to change their view as they learn of more beneficial hybrid events. The Atlantic science journalist Katie Wu https://www.theatlantic.com/author/katherine-j-wu/ details two of these hybridization examples: one in desert frogs and one in two ancient plants that <> led to the modern potato. Interested in more biology episodes? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:21Speaker 01

  Hey, Short Wavers. Producer Burnley 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 of years ago, she was talking to a scientist as part of her recent kick, reporting on frogs.

• 0:39Speaker 02

  As one does. And she was talking to me about hybrids.

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  Hybrids, the result of members of two different species mating. In this case, two different species of frogs.

• 0:51Speaker 02

  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.

• 1:08Speaker 01

  In her reporting, Katie learned that female plains spade-foot 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.

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  The offspring are less fertile, so the males are totally sterile and the females don't produce as many eggs.

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  Because the fitness of hybrid animals across nature is often subpar, like these froggy fertility issues or other health problems, biologists have long thought of interspecies mating as...

• 1:57Speaker 02

  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 in zoos. And this was really the predominant thinking for... Decades and decades and decades.

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  That is, until recently.

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  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.

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  Scientists are finding that sometimes hybrids can form brand-new traits.

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  Neither of its parents could form anything that even looked like a potato, and somehow their offspring did.

• 2:48Speaker 01

  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 Short Wave, the science podcast from NPR.

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• 4:39Speaker 01

  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?

• 4:50Speaker 02

  So I could not responsibly describe for you what two roughly nine million old plants looked like, but we 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.

• 5:19Speaker 01

  Okay, so these are the two parents of the 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's stumped scientists for a long time.

• 5:39Speaker 02

  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.

• 5:48Speaker 01

  I can relate, actually. I think a lot of people can.

• 5:51Speaker 02

  Yeah, potatoes are messy, lots of family drama. But basically, they know that there is 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, you know, potato genomes are really complicated. And they 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, you know, the tomato, one of its parents, we now know.

• 6:30Speaker 01

  This makes sense as a gardener.

• 6:32Speaker 02

  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-tuberism, which is the other parent in the story. But scientists were basically always considering one or the other, tomato or e-tuberism. 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-tuberism. It was a team tomato or team e-tuberism story. Team both was not on the table.

• 7:15Speaker 01

  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-tuberism? And 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?

• 7:44Speaker 02

  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-tuberism 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 know, some ancient potato mixed with e-tuberism and that's how e-tuberism stuff got in the potato genome? Or was it the total inverse? You know, descended from e-tuberism, then mixed with a tomato plant either on? 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

• 8:28Speaker 02

  of tomato and e-tuberism 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 e-tuberism 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 100-plus species we see today. It wasn't that, you know, 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.

• 9:10Speaker 01

  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?

• 9:29Speaker 02

  So I have no idea what the first potato plant looked like, but it probably was not a tomato growing underground.

• 9:34Speaker 01

  Okay, okay.

• 9:34Speaker 02

  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. 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 storage 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.

• 10:12Speaker 01

  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?

• 10:24Speaker 02

  I think the answer for right now is maybe, question mark, probably, question mark. There is not a set in stone plan to, you know, 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, make it easier to work with, maybe that could be really interesting.

• 11:06Speaker 02

  One sort of out of the box idea that some of the scientists who worked on this project are playing with are, you know, using this information to help tomato plants make underground tubers, so making their own potatoes.

• 11:17Speaker 01

  What?

• 11:18Speaker 02

  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.

• 11:32Speaker 01

  My gosh, that would be so amazing.

• 11:35Speaker 02

  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? That's not the same as make-

• 11:50Speaker 01

  You can mash them together and they stay alive and produce both things?

• 11:53Speaker 02

  Yeah. It's not quite the same as coaxing a tomato, like with genetic manipulation to make its own potatoes, but, you know, it's a little bit more like organ donation when you splice the two together. Or a human centipede, whichever metaphor you prefer here. One is a little grosser than the other.

• 12:13Speaker 01

  Yes, I need one of these plants now. So, 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?

• 12:25Speaker 02

  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,

• 13:09Speaker 02

  even potentially human evolution. It seems like there's hybridization in our own evolutionary history. 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.

• 13:29Speaker 01

  Catherine Wu is a science journalist at The Atlantic. See our show notes for both of her articles on hybrids. Thank you so much, Katie.

• 13:37Speaker 02

  Always good to be here.

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  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 Short Wave from NPR.

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