Frogs and tadpoles

Richard Wassersug


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Matt Smith:

Welcome to the La Trobe University Podcast. I'd be you host Matt Smith and this [Ribbit] is a frog. Now I know, I know what you're thinking. It's a La Trobe University Podcast, there's a frog, we've got The Blue Danube playing in the background, any minute now this little green sucker's going to be airborne. But not this time. Today we will be talking with Dr. Richard Wassersug of the Department of Anatomy and Neurobiology at Dalhousie University. He spent his career studying frogs and tadpoles so for now, we'll hold on to the little guy.

Dr. Richard Wassersug:

I've been in the science game for quite some time. When I was in high school, the Russians have launched sputnik and the Americans felt they're way, way, way behind in the space race. And they started funding high school students to do research or be associated with labs not just to do it on their own but actually get a chance to work in a real research lab. And I was a part of a program like that. I worked at Harvard University on a fossil toad, published my first paper on this fossil toad back in the 19 somewhere, back then.

It got me very much interested in the evolution of frogs. All through university and now into graduate school, I realized that there was a fascinating problem with the evolution of frogs. That if you were to lay out, just as a comparative example. Ah, insectivorous mammals, monkeys, higher primates, humans, you can get an actual progression that makes good sense. You can look at a frog, the first one you'll get in the fossil record it looks like a frog. And then you look at anything before it, it looks like salamander, there's nothing in between.

So we didn't know where the frogs came from and how they were built. I got into graduate school and I realized that any answer I came up with about the evolution of frogs would also have to explain the evolution tadpoles and nobody was really looking at tadpoles. So I started studying tadpoles. At first I studied their morphology and ones we had very funny, very complicated structures inside their mouths. Even though it looks so simple, round body with a tail inside their mouths there were all sorts of fancy, fancy particles separating papillae and ridges and so forth.

And that became the beginning of my career. Some of them, some of these strange structures also have strange behaviors. So I started studying their behavior. And then I realized that those that had that strange behavior, the amount of oxygen in the water changed their behaviors so I started studying their oxygen responses and their physiology and I spent most of my career studying, I think I've published about 150 or more papers, on the biology of tadpoles, trying to understand these animals. It's been great fun because I've had the freedom to study every aspect. Their behavior, their ecology, their morphology, physiology and so forth.

Matt Smith:

Are they as diverse as the frogs? And can you kind of get an indication if you look at the tadpole what sort of frog or tadpole you're going to get?

Dr. Richard Wassersug:

Sometimes you can and sometimes you can't. Most of the time it's pretty simple in externally. But if you open them up and look inside their mouths, it turns out they're very complicated. My colleagues and I have done things like use high-speed cameras to try to figure out how they can feed. Some tadpoles can extract from water virus sized particles. And this is a remarkable filter feeding capability. It was questions like that that really started my interest. And there are certain families of frogs which have very specific types of tadpoles so in that situation, if you found the tadpole you'd know what family of frogs it belong to and you could pretty well guess what that tadpole will turn into. Often into this day, in museums there's lots of collections of unidentified tadpoles. Where they found the tadpoles, they never found the frog or never raised the tadpoles long enough to find out what frog they'd turn into. So we still have a fair bit of work for those who are interested on a group of organisms that are still fairly unstudied to figure out what some of the tadpoles are and matching them to the adult frogs.

Matt Smith:

You were awarded an Ig Nobel Prize for Research Involving Tadpoles. Can you tell me a bit about that? It was 30 years after you published the paper wasn't it?

Dr. Richard Wassersug:

Ah yes it was.

Matt Smith:

So it must come as a bit of a surprise?

Dr. Richard Wassersug:

Yes it came a bit as a bit of a surprise because frankly I thought there were lots of better studies in those 30 years worthy of an Ig Nobel Prize.

So the Ig Nobel Prizes were ah, satirical and generally critically satirical awards given out every year. A guy who runs this program out of Harvard is a guy named Marc Abrahams. He also publishes the Annals of Improbable Research a science humor magazine. Early on, this is the way it's phrased, either research couldn't or shouldn't be duplicated. It was making fun of research that was pretty bad or perhaps even dangerous.

I have to say regrettably but I guess I should acknowledge this, my research is of the school and it shouldn't be duplicated but could be duplicated but shouldn't be, because in fact as I look back now I realized it was pretty dangerous what I did. But I was in the tropical biology class in the jungle in Costa Rica for a two-month course and at the end of the course we had three days sort of independent study program.

And in one of these I realized is that some of the tadpoles were really easy to see, find, and collect. Real easy. And if they're really easy for me to see, find, and collect, one might imagine it would be really easy for birds and other animals to see, find, and collect and I thought that if they're going to survive they probably would taste terrible.

And then there were other tadpoles that lived individually under rocks and fast flowing streams where you'd stand in the stream with a special net roll over a rock and you'd be lucky if you could catch one tadpole in an hour. And I thought well they can hide. They're cryptic, they're hard to find. Maybe they taste differently. The only catch for us is how do I find the predator that would eat tadpoles on the spur of the moment. So I went for the easiest conditioned organism I could find which were my fellow graduate students. And with a bribe of beer, an embarrassment there as well, I got them to join in a tadpole tasting project with me and then to eat the tadpoles that were easy to find tasted terrible.

They are the worst tasting tadpoles in the world and this actually in the Australian hedges because they turned out to be Bufo Marinus, the cane toad, that's the invasive toad that has taken over the territory in Australia partially because the tadpoles of the adults taste so bad that nobody eats them. So I wrote this paper up and 30 years later I got myself an Ig Nobel Prize. I would like to say in my own defense, I didn't file human ethics, I mean nowadays I wouldn't have done this study, it is too risky. We didn't swallow them by the way. I had people spit them up but the toad tadpoles, the cane toad tadpoles were the most bitter thing I have ever tasted in my whole life, they are terrible.

Matt Smith:

Also in your defense, self experimentation isn't exactly new.

Dr. Richard Wassersug:

Many people have done in fact self experimentation and some Nobel Prizes have been one for people who had the courage to do this type of stuff. The person to do imaging of a catheterization of the heart, put a dye into the heart who actually ran the line up his own arm and stood in front of his own x-ray machine got, he got a Nobel Prize for that. I appreciate that mindset of self experimentation and I think I do respect that. But at the same time that was a dangerous experiment.

Now I might say if I can a little more about the Ig Nobel Prizes, they've changed their theme. Over the years they become much more interested in, research that is not stupid or evil or shouldn't be reproduced. But now the slogan is research should first makes you laugh and then makes you think. And I think that's ah, a much better slogan than I mean what's happened also over the years, it's been ten years since I won that award, the Ig Nobel Prize, I've become a fair bit more respectable particularly because of one gentleman who won one when I was there.

He won the Physics one. His name was Andre Geim and last year he, he won a Nobel Prize. It takes some creativity to both do wacko science and do useful wacko science. But you still have to have be a bit creative and I think the awards now are going to creativity. And I'm sort of proud that I pulled this off and actually got to publish it on paper with less than three days of work.

Matt Smith:

What sort of work are you doing with tadpoles now? Do they get much of a look in?

Dr. Richard Wassersug:

Yes I am still working with tadpoles. We have one paper in press and I published three or four last year. And they're all related to another and very serious problem affecting tadpoles. Unfortunately, these animals that I love and have studied for so long in so many places in the world are now dying off. And dying off not just in terms of a few or single species but species in general and whole communities. Multi-species communities are disappearing. There are a variety of reasons why. We don't know what the primary one is but one of them involves a fungal infection that affects the mouth parts of tadpoles.

Well I started my research on tadpoles way back when looking at the mouth parts. So we're interested in how and I've been publishing them, how these mouth parts actually work when they're affected by this fungus and whether the fungus attacking the mouth parts is really what's killing off the tadpoles because the fungus could also affecting internally the organs and therefore it's lethality maybe related to that.

One of the things we've shown is that in fact it is simply the damage they do to the mouth parts that is the most serious hit to the tadpoles. And now how you control this fungus and all that we don't know. What this led us to do is use high speed video imaging of the mouth parts and actually studied the details at 500 frames a second is its high speed. To look at how they use these very, very complicated little structures in order to scrape food off the surfaces and so forth. And they do it fast and they do it elegantly. As simple as they are and as mindless as they appear to be they turn out to have a very elaborate and elegant feeding structures and feeding behaviors.

And understanding that, may hopefully somehow help us understand ways of perhaps protecting them from disappearing or at least tell them what foods are best for them and so forth. So all my work with tadpoles right now tends to be focused on that. We've also won the odd study that I did, which was looking at the shape of the aquatic environment that tadpoles are raised in so we built aquaria which were truncated frusta they were a pyramid with the top cut off. And this way, we are changing the slope on the sides. We could keep the water depth the same or the water surface area the same or their volume the same and keep to the three variables the same while changing only one.

Then we can ask whether it mattered for instance if you raise tadpoles into groups of the same volume of water but different depths or the same volume of water, the same depth but different surface areas whether that made the difference. We found, there's an example. Tadpoles that live in large bodies of water suffer in shallow water because of the depth and not because of the volume. They have a problem reaching the surface and taking a bite of air when they're air breathers, which they can't do if the water is too shallow. And this has ecological implications because we're concerned about global climate change leading to ponds drying. What the study suggests is the pond's don't even have to dry up fully to put the tadpoles in jeopardy. And in fact they don't even have to get overheated or they don't have to have a decline in the oxygen just by lowering the depth of the water, the tadpoles will be in trouble. So this is really ecological implications and I'm concerned about that. I haven't given up working on tadpoles and hope to continue working a bit more with them in the future.

Matt Smith:

That's all the time we've got for the La Trobe University Podcast today. If you have any questions, comments or feedback, you can send us an email at Dr. Richard Wassersug thank you for your time.

Dr Richard Wassersug:

You're welcome, thank you very much.