Snakes Are Evolutionary Superstars

IRA FLATOW: Ever since those reported events in the Garden of Eden, snakes have been given a bad rap. Love them or hate them, turns out that snakes are some of the most evolutionarily elite creatures on the planet. And it’s not just me who’s saying this. A new study in the journal Science finds that snakes evolve faster than other groups of lizards. Yeah, and their ability to adapt to hyper-specific diets and circumstances make them winners among vertebrates. So what do you think about snakes now?

Well, joining me to share the science of serpents is its Senior Author Daniel Rabosky, Evolutionary Biologist and Curator at the Museum of Zoology, University of Michigan, based in Ann Arbor. Welcome to Science Friday.

DANIEL RABOSKY: Thanks so much for having me, Ira.

IRA FLATOW: I want to get right into this. Why are snakes such an evolutionary powerhouse?

DANIEL RABOSKY: That’s a really good question. Why are snakes such a powerhouse? I think that first, it’s not immediately obvious to maybe a lot of folks just how different snakes are within reptiles. But you look at a variety of traits, and you can see this really profound shift between other groups of lizards and snakes. And that’s one of the things that we document in our study that really carries through to numerous aspects of their ways of life and their structure.

So obviously, yes, this raises this big question of why. And in some ways, we set out to answer the question about this evolutionary shift and what drives these kinds of evolutionary differences in what different groups of lizards do. And part of our answer that we find is that snakes are simply doing things faster. Their evolutionary engine is running hotter.

IRA FLATOW: What do you mean by that? Give me an example. How do we know that?

DANIEL RABOSKY: That’s a great question. So we know this because one of the things that we are able to do in our study, for example, and within modern evolutionary biology more generally, is take some of these types of data that we can get from genomes, for example, and from ecological data, like what things eat, and we can use statistical methods to figure out how fast things are evolving with respect to those kinds of features, like the shape of their skull or the things that they eat.

So we can tell you that snakes, for example, are evolving new kinds of– a given lineage of snake is evolving essentially faster. It’s exploring this diet landscape of potential dietary items more rapidly than the average lizard, for example.

IRA FLATOW: Wow.

DANIEL RABOSKY: And so the sort of statistics of it– it gets a little technical, but that’s the basic idea.

IRA FLATOW: Did you say there are legless lizards that may look a lot like snakes to the untrained eye, but they’re totally different?

DANIEL RABOSKY: That is correct. So there are a number of fine anatomical differences that separate snakes out as a group within the lizards. But there are many groups of lizards that superficially are snake like. And so let’s say, I could pick many examples of lizards that have evolutionarily lost their legs where I could hand them to someone and say, is this a snake or a lizard? And people would be like, it’s a snake. But actually it’s a lizard, and it’s distinct from snakes.

Now, that’s one of the interesting things that we find in our study is that when these other groups of lizards evolve on this snake-like trajectory– so they essentially discard their limbs, you might say– well, there’s something about being a long, legless thing that sort of predisposes you to maybe evolving faster or specializing in the kinds of dietary things that snakes do.

And that’s really not what we see at all. For the most part, the lizard groups that lose their legs other than snakes have essentially stayed lizard like. And so it’s really remarkable that the things that have gone down this snake trajectory haven’t done what snakes have done, which raises other questions about why.

So the other ones that are essentially still specializing on the kinds of foods that typical lizards would specialize on, or they’re not doing the same, they’re not using as diverse of habitats. They’re living a burrowing type lifestyle, for example, more often than not.

IRA FLATOW: So where do snakes have, so to speak, a leg up on lizards?

DANIEL RABOSKY: In what sense do snakes have a leg up on lizards? Well, what do we mean by a leg up? So in one sense, snakes have been tremendously successful. Of course, lizards have been hanging around for a long time as well. Where snakes have really shined, though, is in terms of their ability to become ecologically diverse, especially over the past 65 million years or so.

There are a lot of species of lizards, of course. But I think snakes have managed to exploit a broader range of habitats on the surface of the Earth and a broader range of ecological ways of life and diverse dietary strategies, and so on. And so I think that one of the things that has set snakes up for, in the last 65 million years, is it’s an ability to take advantage of certain types of opportunities that have happened in Earth history.

And one of the things that we see as we see a signal of after, for example, probably in the wake of the mass extinction that wiped out the non-avian dinosaurs, is a flourishing of snake diversity that kicked off in the 10 million years or so after that. That’s a pretty strong signal that shows up in the snake record.

And I do think that it might have something to do with that underlying evolutionary speed or that evolutionary potential that snakes have that essentially has let them take advantage of new environmental or ecological opportunities, or if you want to think about them as empty ecological niches.

IRA FLATOW: Give us a couple of examples of snakes that develop specific niches in their diets.

DANIEL RABOSKY: There are– I mean, the catalog is vast. Here, I will list a few. I’ll give you a few of my favorite examples. I think that one of the things about snakes that really separates them from lizards and something that we show, I think well, in our study is that snakes are much more dietarily specialized than the average lizard.

And so one of the things that you see within snakes are these incredibly interesting dietary strategies. For example, there are species of snakes that specialize on feeding on essentially these soft-bodied mollusks, like snails and slugs that live in trees. And they’re defended by these heavy mucous secretions.

And these snakes have a number of specialized adaptations to feed on these things. And that, for the most part, will be the primary diet of those species. Or there are species of snakes that are sea snakes that have these long paddle-shaped tails. And they can dive down into coral reefs. And they are specialists on things like fish eggs. So they just probe through crevices in coral reefs and look for fish eggs and essentially scrape them off that coral structure down there.

There are many species of snakes that are specialized predators of other snakes. So they are specialist hunters of other species of snakes. So the list goes on and on. There are species of snakes that specialize only on feeding on larval termites. There are some groups, some species, that tend to feed quite a bit on tree frog eggs.

And there’s some interesting issues there with tree frog eggs essentially evolving the ability to sense when a snake is eating them. And they will hatch when they sense a snake starting to eat their little clutch of eggs. It’s kind of remarkable behavior that happens in tropical rainforest frogs.

IRA FLATOW: You just blew my mind on that one. Wow. How were you able to investigate these interesting dietary habits of snakes? I mean, did you just hang around and watch them?

DANIEL RABOSKY: That is a good question. So how do we get all this dietary information on snakes and lizards? So it turns out that for the vast majority of species of snakes and lizards, there are virtually no or very few observations of these animals doing their thing feeding in nature. They’re very cryptic. They’re very camouflaged. They live in parts of the world that are hard to get to.

And so as a result, we’re very information poor about what these animals do in nature. And so what we exploited in our study is this spectacular resource in the form of natural history specimens, or specimens in our natural history museums, where there might be thousands of preserved snake or lizard specimens that come from a variety of sources.

And you might imagine that these things have within their stomachs a sort of record of what they’ve been eating. So we were able to go to this vast storehouse of natural history specimens and look inside their guts, essentially, and figure out what these things were eating. And I would add that that’s really the only way that we have about what a lot of animals are doing ecologically in terms of diet in nature.

So it’s a really important source of insight into what animals do in the wild that frankly is very difficult to get in the wild through what you might think of as just going out and observing nature.

IRA FLATOW: Is it possible to watch today snake evolution as it happens quickly? And I’m thinking specifically as we have our climate crisis and things are warming up, getting wetter, getting drier. Can we watch snakes evolve in our lifespan?

DANIEL RABOSKY: I would give two parts of an answer to that. First, I would say absolutely that we can see snakes evolving. In fact, we can see lots of things evolving in real time. Pretty much everywhere we look, when we take the time to do a careful study of it, we see evolution unfolding in real time within populations.

However, I would caution that it’s really difficult to go beyond that to make any kind of projections about whether snakes could adapt to the pace of change in the world around us today. I would say that you’re looking at very different time scales in terms of rate of evolution. We’re measuring things that are happening in our study over things that are happening over millions of years.

And right here, we’re changing things in the space of decades. So it’s just not the same sort of time scale. And I would be very cautious about making any projections. I think that I would not read into that as saying that snakes are going to be able to manage some of these types of environmental changes.

IRA FLATOW: Has your admiration for snakes increased as you study them?

DANIEL RABOSKY: Well, I don’t know. My admiration was pretty high going into this. So I think I have a newfound appreciation for some dimensions of snake biology that I would not have maybe been aware of prior to starting this. I would add to that, we have tremendous areas of the snake or the snake and lizard tree of life that are very data deficient, where we have very little information about the basic biology of these animals in nature.

And so while it seems like we have a lot of data in our paper, and in fact we do, at the same time, it’s really clear when you look at where those data are across the surface of the Earth that we have diet data for, like, 15% of species. Gaining that data was a lifetime of work for many, many researchers.

And we’re in a world where we’re changing climate very quickly, and we don’t have the most basic information about many species of lizards and snakes and many other things, too. And I do think that in 10 years, 20 years, 50 years down the road, we are really going to regret that we did not go all out at collecting some of this information because a lot of these populations and many of these species unfortunately are not even going to be with us. We’re going to have little understanding of what roles they’re playing within their systems.

IRA FLATOW: Well Daniel, I’ve learned so much about snakes today. I want to thank you for taking time to be with us.

DANIEL RABOSKY: Thanks so much for having me on the show.

IRA FLATOW: Great stuff. Daniel Rabosky, Evolutionary Biologist and Curator at the Museum of Zoology, that’s at the University of Michigan in famous Ann Arbor.

Copyright © 2023 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/