AILSA CHANG, HOST:
Toads have taken over the world - for real. This isn't some horror movie I'm talking about. This is actually happening, people. Don't freak out, but toads have found their way onto six out of the seven continents. I guess the climate of Antarctica isn't great for amphibians. Anyway, toads originated in South America, so how did they end up dominating so much of the rest of the world? Well, a new study out this month tells us how. Christopher Raxworthy is a herpetologist and a curator at the American Museum of Natural History in New York. He's also one of the study's coauthors. We spoke recently about how this slimy, chunky creature has made its way all around the world and why that is so important.
CHRISTOPHER RAXWORTHY: We don't know for certain, but there's two main hypotheses - two routes they could have done. The first is they could have gone through Antarctica, which is...
CHANG: (Gasping).
RAXWORTHY: ...You know, a wild idea.
CHANG: Yeah.
RAXWORTHY: That's the one continent where we don't have toads now.
CHANG: Yeah.
RAXWORTHY: But 30 million years ago, the climate was a lot warmer, so the distances between land masses then would have been quite a bit closer. So they could have gone into Antarctica and then from Antarctica into southern Africa.
CHANG: Cool.
RAXWORTHY: But perhaps a more likely route is actually them rafting across the Atlantic Ocean. And that...
CHANG: Rafting?
RAXWORTHY: ...Sounds - yeah, crazy, right? But...
CHANG: They built little rafts? No. Come on. Tell me how (laughter).
RAXWORTHY: No. But if you ever have been in the tropics in a major rainstorm, you will see, you know, rivers just with huge amounts of water coming down them, banks of rivers...
CHANG: Yes.
RAXWORTHY: ...Slipping and trees and mats of vegetation being washed out to the oceans. And toads often live in rotten logs and in cavities in mud banks. And so you could easily imagine, you know, rafts of vegetation getting washed out into the ocean. And toads are tough guys. They have...
CHANG: Wow.
RAXWORTHY: ...Thick skins. They're more resistant to dehydration. And so all you would need is ultimately one lucky group of toads on a mat of vegetation...
CHANG: (Laughter).
RAXWORTHY: ...To get washed up on a beach in Africa, and they're on their way. The other thing about toads, though, that gave them an edge was they're highly toxic now. They have these big parotid glands on their necks. That is actually an antipredator device. And what we also established in our study is that this time of toad invasion is associated with these glands evolving.
CHANG: Wow. OK, well, as we mentioned, Antarctica, right now, doesn't have toads. Could we one...
RAXWORTHY: Yeah.
CHANG: ...Day see toads living in one of the coldest places on Earth? - 'cause you're telling me they have really thick skins.
RAXWORTHY: Right.
CHANG: Maybe they're going to get thicker.
RAXWORTHY: Well, there's two interesting things about that. So first of all, we actually have - believe it or not - now found fossil amphibians from Antarctica which, you know, document that warmer period in their...
CHANG: Yeah.
RAXWORTHY: ...History. And toads are still spreading and getting into the final corners of the world that they haven't invaded. So they're getting a help now with humans. Australia had no toads until the 1930s, when they were introduced as a biological control. And in 2010, the Asian toad got into Madagascar, probably in a shipping container...
CHANG: (Laughter).
RAXWORTHY: ...In a shipment of rice. And so they are expanding their range still to get to these, you know, remote corners of the world.
CHANG: So maybe there are some people listening right now and thinking, why do I even care about these toads and why they ended up in my backyard? Come on. Why are these findings of this study so significant, Christopher?
RAXWORTHY: Right. Well, I think toads in themselves are beautiful animals and worthy of study.
CHANG: (Laughter).
RAXWORTHY: If you look into an eye of a toad, it's like, oh, it's fantastic. But...
CHANG: Really? Oh, you connect...
RAXWORTHY: ...If you are not convinced by...
CHANG: ...With the toads' eyes (laughter).
RAXWORTHY: Yeah. If you're not convinced by that, then if you talk to gardeners, they'll always refer to toads as the gardener's friend. They eat slugs and pests. But I think also, fundamentally, understanding about the relationships between different species, for example, predators and prey, and also understanding about what traits of species actually mean that they're successful, that they produce more species - even understanding in the process of speciation - we can learn all of these different processes from toads.
CHANG: Well, Christopher, you have inspired me to look straight into a toad's eyes the next time I see a toad.
RAXWORTHY: They're wonderful.
CHANG: (Laughter) Christopher Raxworthy, curator of herpetology at the American Museum of Natural History in New York City. Thank you so much. This was so fun.
RAXWORTHY: Thank you. Transcript provided by NPR, Copyright NPR.
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