Evolution in Action
Air Date: Week of July 15, 2011
Biologists at American University are tracking evolutionary changes in the red-shouldered soapberry bug. In just 50 years, the bugs’ beaks have become shorter and they are making more babies. As Ari Daniel Shapiro reports, researchers are excited about these rapid adaptations and want to know just which genes make this bug diversity possible.
YOUNG: Evolution has slowly, slowly shaped life on our planet, with genetic adaptations arising over the millennia. But that’s not always the case. Sometimes you can actually watch something evolve in real time. Ari Daniel Shapiro has our story.
SHAPIRO: When you keep red-shouldered Soapberry bugs, that’s Jadera haematoloma – in the lab, it’s only a matter of time before one’s on the loose.
ANGELINI: Whoop. Great.
SHAPIRO: David Angelini moves vials and flasks to the side…
ANGELINI: Come here…
SHAPIRO: …as he corners a female Soapberry bug who’s scuttling away. Angelini’s a biologist at American University.
ANGELINI: Here we go.
SHAPIRO: At last he picks up the thumbnail-sized bug and places her on what looks like a mini air hockey rink. Low levels of carbon dioxide pour out of the little holes, gradually anesthetizing the bug.
[SOUND OF MICROSCOPE ADJUSTING]
SHAPIRO: Angelini adjusts the focus of his microscope and I peer down at her. She’s beautiful. Her wings are a glittery black.
ANGELINI: Yeah, looks like asphalt after a rainstorm. It’s very nice.
SHAPIRO: And right where her wings connect to her body are two flashes of bright red. Angelini’s eager to show me her other side.
ANGELINI: We can flip her over. She won’t object.
SHAPIRO: She’s that same bright red underneath. And she’s got a lineup of little black appendages.
ANGELINI: The antennae, the legs, the genitalia, the mouthparts.
SHAPIRO: These mouthparts are called the beak, and it looks like a long straw.
ANGELINI: It looks more like an elephant trunk, honestly.
SHAPIRO: Except that it doesn’t extend out in front. The beak tucks under a Soapberry bug, pointing backwards. It works like a tiny syringe that can pierce the dark, round seeds of a plant called the Balloon vine.
ANGELINI: That’s Cardiospermum, a native vine in Florida and the U.S. Southeast.
SHAPIRO: Before the Balloon vine releases its seeds though, they grow inside these leafy capsules or pods shaped like little balloons.
ANGELINI: The pod is full of air. It’s just the covering keeping bugs away from the seeds.
SHAPIRO: But the pods don’t keep a Soapberry bug away. It perches itself on the balloon, punctures the pod with its beak, and skewers the seeds inside. The beak’s the perfect size to do the job – about 70 percent of the bug’s total length. Or at least that’s how big it was before 1950.
[DOOR NOISE AND THE SOUNDS OF WALKING ACROSS CAMPUS]
SHAPIRO: Angelini and his graduate student Stacey Baker walk me across campus towards the chemistry building.
BAKER: So right outside of that building is where the Goldenrain tree is.
SHAPIRO: The Goldenrain tree, or Koelreuteria peniculata, is originally from Taiwan. But around 1950, this tree – among others – was shipped to Florida for landscaping purposes. And the Goldenrain tree – it’s related to the Balloon vine. It has the same kind of leafy pods, except a little smaller. It’s got the same sort of dark round seeds. And it wasn’t long before the Soapberry bugs of Florida started dining on them. In the last 60 years, Goldenrain trees have been planted throughout the US, as far west as California and as far north as Washington DC; in backyards, in gardens and on college campuses like American University where Angelini works.
ANGELINI: When I first started this, I had no idea how prevalent Goldenrain trees were. We started getting tips so we drove all over creation looking for them, and then we discovered this one right on our doorstep, so…
SHAPIRO: Sorry, was that one of them?
Baker: Yes, so this is a baby.
ANGELINI: The really large tree that’s behind these hollies, that’s a Goldenrain tree.
SHAPIRO: You know, it’s funny. They don’t look out of place. They blend right in.
ANGELINI: I know, a Taiwanese tree, but here in DC you’d never know that it was anything special.
SHAPIRO: And as the trees have traveled the U.S., so have the Soapberry bugs.
ANGELINI: So this sidewalk and down by the base of that tree is where we’ve actually collected most of the bugs that we used.
SHAPIRO: Used, that is, back in his lab.
[SOUNDS OF LAB DRAWER OPENING, GLASSWARE CLINKING]
SHAPIRO: You see, Angelini studies evolution. And something remarkable has happened to the population of Soapberry bugs feeding on Goldenrain tree seeds. They’ve adapted. Fast.
ANGELINI: It was discovered that their mouthparts were now about 30 percent shorter.
SHAPIRO: That’s because the seedpods were smaller. And that’s not all.
ANGELINI: They were making more babies, the babies lived at a higher rate, and their flight muscles were also smaller. Basically all this evolutionary change had happened in about a hundred generations, so in about 50 years. And in evolutionary terms that’s remarkably fast.
BAKER: Very fast cause if you think about evolution we think millions of years, thousands of years. We can see it in a lifetime.
SHAPIRO: Baker and Angelini want to know which of the Soapberry bug’s 15 thousand genes have made these evolutionary changes possible. But it’s not just about this bug.
ANGELINI: I mean, it’s easy to look around in the world and see biological diversity and that arises through evolution. And what we really want to do is we want to be able to understand at a fundamental, at a genetic level, what is producing this diversity that we see.
SHAPIRO: Darwin’s theory of evolution relied on observing species that had already diverged from one another. But the Soapberry bug is an example of evolution in action – in the wild. And inside the span of a single researcher’s career. Angelini wants to know all the genetic differences between the new population of bugs on the Goldenrain tree and those still living on the Balloon vine in Florida. That’s the big dream. But until then, he and Stacey Baker will go on corralling hundreds of Soapberry bugs.
BAKER: Got ’em.
BAKER: Oop, lost ’em.
SHAPIRO: For Living on Earth, I’m Ari Daniel Shapiro.
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