TED日本語 - ジャープ・デ＝ローデ: 自ら治療する蝶

So infectious diseases, right? Infectious diseases are still the main cause of human suffering and death around the world. Every year, millions of people die of diseases such as T.B., malaria, HIV, around the world and even in the United States. Every year, thousands of Americans die of seasonal flu.

Now of course, humans, we are creative. Right? We have come up with ways to protect ourselves against these diseases. We have drugs and vaccines. And we're conscious -- we learn from our experiences and come up with creative solutions. We used to think we're alone in this, but now we know we're not. We're not the only medical doctors. Now we know that there's a lot of animals out there that can do it too. Most famous, perhaps, chimpanzees. Not so much different from us, they can use plants to treat their intestinal parasites. But the last few decades have shown us that other animals can do it too: elephants, porcupines, sheep, goats, you name it. And even more interesting than that is that recent discoveries are telling us that insects and other little animals with smaller brains can use medication too.

The problem with infectious diseases, as we all know, is that pathogens continue to evolve, and a lot of the drugs that we have developed are losing their efficacy. And therefore, there is this great need to find new ways to discover drugs that we can use against our diseases.

Now, I think that we should look at these animals, and we can learn from them how to treat our own diseases. As a biologist, I have been studying monarch butterflies for the last 10 years. Now, monarchs are extremely famous for their spectacular migrations from the U.S. and Canada down to Mexico every year, where millions of them come together, but it's not why I started studying them. I study monarchs because they get sick. They get sick like you. They get sick like me. And I think what they do can tell us a lot about drugs that we can develop for humans.

Now, the parasites that monarchs get infected with are called ophryocystis elektroscirrha -- a mouthful. What they do is they produce spores, millions of spores on the outside of the butterfly that are shown as little specks in between the scales of the butterfly. And this is really detrimental to the monarch. It shortens their lifespan, it reduces their ability to fly, it can even kill them before they're even adults. Very detrimental parasite.

As part of my job, I spend a lot of time in the greenhouse growing plants, and the reason for this is that monarchs are extremely picky eaters. They only eat milkweed as larvae. Luckily, there are several species of milkweed that they can use, and all these milkweeds have cardenolides in them. These are chemicals that are toxic. They're toxic to most animals, but not to monarchs. In fact, monarchs can take up the chemicals, put it in their own bodies, and it makes them toxic against their predators, such as birds. And what they do, then, is advertise this toxicity through their beautiful warning colorations with this orange, black and white.

So what I did during my job is grow plants in the greenhouse, different ones, different milkweeds. Some were toxic, including the tropical milkweed, with very high concentrations of these cardenolides. And some were not toxic. And then I fed them to monarchs. Some of the monarchs were healthy. They had no disease. But some of the monarchs were sick, and what I found is that some of these milkweeds are medicinal, meaning they reduce the disease symptoms in the monarch butterflies, meaning these monarchs can live longer when they are infected when feeding on these medicinal plants.

And when I found this, I had this idea, and a lot of people said it was a crazy idea, but I thought, what if monarchs can use this? What if they can use these plants as their own form of medicine? What if they can act as medical doctors?

So my team and I started doing experiments. In the first types of experiments, we had caterpillars, and gave them a choice: medicinal milkweed versus non-medicinal milkweed. And then we measured how much they ate of each species over their lifetime. And the result, as so often in science, was boring: Fifty percent of their food was medicinal. Fifty percent was not. These caterpillars didn't do anything for their own welfare.

So then we moved on to adult butterflies, and we started asking the question whether it's the mothers that can medicate their offspring. Can the mothers lay their eggs on medicinal milkweed that will make their future offspring less sick? We have done these experiments now over several years, and always get the same results. What we do is we put a monarch in a big cage, a medicinal plant on one side, a non-medicinal plant on the other side, and then we measure the number of eggs that the monarchs lay on each plant. And what we find when we do that is always the same. What we find is that the monarchs strongly prefer the medicinal milkweed. In other words, what these females are doing is they're laying 68 percent of their eggs in the medicinal milkweed. Intriguingly, what they do is they actually transmit the parasites when they're laying the eggs. They can not prevent this. They can also not medicate themselves. But what these experiments tell us is that these monarchs, these mothers, can lay their eggs on medicinal milkweed that will make their future offspring less sick.

Now, this is a really important discovery, I think, not just because it tells us something cool about nature, but also because it may tell us something more about how we should find drugs. Now, these are animals that are very small and we tend to think of them as very simple. They have tiny little brains, yet they can do this very sophisticated medication. Now, we know that even today, most of our drugs derive from natural products, including plants, and in indigenous cultures, traditional healers often look at animals to find new drugs. In this way, elephants have told us how to treat stomach upset, and porcupines have told people how to treat bloody diarrhea. What I think is important, though, is to move beyond these large-brained mammals and give these guys more credit, these simple animals, these insects that we tend to think of as very, very simple with tiny little brains. The discovery that these animals can also use medication opens up completely new avenues, and I think that maybe one day, we will be treating human diseases with drugs that were first discovered by butterflies, and I think that is an amazing opportunity worth pursuing.

Thank you so much.

(Applause)