SPEAKER: This is a production of Cornell University Library.
MARY OCHS: Thanks for coming, everybody, today. I guess we'll get started. I'm Mary Ochs. I'm the director of Mann Library. And welcome to our Chats in the Stacks talk today. Just a few words of introduction.
It's a busy month here at Mann Library. We have a new exhibit in the lobby that focuses on the early 18th century botanist Mark Catesby, which just opened, and you'll see it on your way out. We have a book talk about Mr. Catesby scheduled for April 26.
And then also, there's some information on the back table. We're having an Earth Day Film Festival here in this room on April 21st, so another event to watch for. You can also sign up for alerts from us if you want to make sure you hear about our programs. So there's a sign-up sheet on the back table.
I'd like to take a minute also to remember a good friend of Mann Library. Some of you may have known Professor Mary Morrison. She was a great friend of Mann Library and a wonderful professor here at Cornell. And she endowed the Mary Morrison Public Education Fund, which helps us support these programs. And Mary died a couple months ago over the winter, so we're missing her a lot and wanted to just let those of you who knew Mary know that she's one of the big supporters of this program.
And last but not least, our friends from Buffalo Street Books are in the back of the room. So if, at the end of the talk or during the talk, you're inspired to go buy a book, you can find them in the back.
So it's now my pleasure to introduce our speaker today, Professor of Ecology and Evolutionary Biology, Anurag Agrawal. A native of Pennsylvania, Dr. Agrawal received his BA and MA degrees from the University of Pennsylvania and his PhD in population biology from the University of California, Davis. After his postdoc work at the University of Amsterdam and a faculty appointment at University of Toronto's Department of Botany, Dr. Agrawal joined the faculty at Cornell in 2004, where he teaches both undergraduate and graduate level courses in field ecology, chemical ecology, community ecology, and plant-insect interactions.
In his lab, Dr. Agrawal's research program explores the ecology and evolution of interactions between plants and animals with particular focus on the antagonistic interactions between plants and insect herbivores. Dr. Agrawal's work has received wide acclaim. In 1999, he received the Young Investigator Award from the American Society of Naturalists, earned distinction with an Early Career Award from the National Science Foundation in 2004, and in 2009, won the David Starr Jordan Prize for innovative contributions in the field of evolutionary biology.
Continued recognition given to Dr. Agrawal over the years, including most recently, the Robert H. MacArthur Award by the Ecological Society of America in 2016, underscores the remarkable impact that he is making on our understanding about key evolutionary relationships in the life sciences.
Among students here at Cornell, Dr. Agrawal is also known as an outstanding educator. And I see some students in the audience here, so that tells us that. Students describe him as, and I'm quoting here, "clear," "concise," "fun," "approachable," "really smart," "a teacher who clearly loves to teach and who teaches by telling awesome stories about the complex intricacies of our natural world." Please join me in welcoming Dr. Agrawal.
ANURAG AGRAWAL: Thanks, everybody, for coming. Whew, it's definitely the hardest to speak in front of the home audience. But here we go. I'm glad to be able to share with you the end of this-- well, not the complete end-- of this journey of writing this book on Monarchs and Milkweed, which started three years ago or so. And it really is-- I mean, it's great to be in this place at the end and to share with you some of the stuff that has come out of it.
In today's talk, I'm going to sort of share with you three vignettes. They don't correspond to particular chapters or whatever in particular, but just some interesting tidbits from the book and the research that I did for it. And I guess I'd say that I'm also very open to questions if you have-- maybe except from you, Michael-- if you have questions during the presentation. I'm happy for you to-- it sort of breaks me up, and that's good.
And then maybe at the end of each of these kind of three sections, we can also have questions then. But I have some number of slides now, I'm afraid. There'll be plenty of time, and I welcome your questions both sort of about what you read in the newspaper, what's happening in your garden, or the co-evolutionary aspects or whatever.
So here we go. The three topics I want to cover relate first to, really, the natural history of the monarch milkweed interaction, and that's covered under this term we call co-evolution. I'll explain a little bit about what I mean by that. I'll next be talking about cultural history and in particular, how the particular chemical compounds that dominate the milkweeds have really been used and abused by humans for thousands of years. And then what we hear a lot about in the news, I'll talk about conservation a little bit, and what's happening with the monarch butterfly populations, and what might happen to it in the future.
So by way of introduction, just a tiny bit about me-- I moved to Ithaca in 2004. As Mary said, it was around several changes in my life around that time. One, Jasper, our first child, our son was born in the same year. You can see what he spent some of the first year of his life doing, rearing butterflies for Dad.
But it's really also around the time when-- this is my daughter, Anna, who's here in the corner-- often can be found looking under the microscope at home-- it's around the time when I really, I'd say, focused in on or became obsessed even more with monarchs and milkweed. And although the people, and the students, and postdocs, and staff in my lab will do many other things and work with other organisms, it's around that time became the focus of my own obsessions.
And to introduce you to the organisms, this is a monarch butterfly that is just emerging from a chrysalis. You can see here is the-- well, you'll see in a minute, it looks often like a kind of jade green dumpling. But when it pops out, it's no longer that way. There are some of the gold dots that are maybe familiar to you on the chrysalis. The monarch pops out, and in about 10 minutes, has to inflate its wings and begin to harden them up.
On the plant side of things, the common milkweed is the star of this story. It's Asclepias syriaca. The genus name is Asclepias, and that was given, endowed to the plant by Linnaeus. Linnaeus had a little bit of misinformation that he propagated. And so the reason it's called Asclepias syriaca is that it was thought that the plant came from the Middle East, from Syria. But it's native to eastern North America. It ranges from New Brunswick to the Carolinas. And it shares, really, an intimate association with this butterfly, the monarch-- among other herbivores. There's another little weevil up there that's feeding on this one.
And where I want to start in terms of the co-evolutionary story-- excuse me-- is at the natural history of how the interaction between monarchs and milkweeds unfolds late in every spring or early in every summer. Right now-- in fact, last week I was in Texas-- there were monarchs there. They are laying eggs, and they're moving north. And I expect, given that it's a rather early spring, they're going to be here probably in mid-May.
The earliest I'd ever seen them was 2012. May 5 in 2012, in front of my house, there was a monarch butterfly laying an egg. I thought it was a practical joke that somebody had played, releasing butterflies there. But I guess they're going to be early this year also. And maybe in an average year, if we ever have average years anymore, the monarchs are arriving-- I don't know-- late June or mid to late June.
And as they're flying north, sometimes they arrest in central New York in Ithaca, and they kind of lay some eggs here and hang around. And other times, they're flying north. They see patches of milkweed, they lay eggs, and then they continue to move. In any case, the seed might look something like this-- a relatively young milkweed plant coming out from its dormant root stocks in the winter. And on the underside of a leaf, we might find a monarch butterfly's egg.
Some four to six days later, depending on temperature, that egg hatches. And hence commences the natural history of co-evolution. And the natural history of co-evolution involves the plant mounting a barrier, some form of armament, to reduce consumption by this caterpillar, and some adaptation, some behavior, some trait of the butterfly that tries to overcome that. And the way it plays out is it plays out a little bit like an arms race, or an escalation in the plant strategies and the animal or the butterfly strategies.
We can kind of watch sort of a play of that in what I call ecological time over the days after which that caterpillar hatches, but really, the evolution and the adaptations take place over millennia, over a much longer time. And what we see in the behaviors are sort of the manifestations of that long term history. So the egg hatches. And the first barrier to feeding for the caterpillar is a bed of hairs.
I think you can see this. All around here, it's sort of like my arm-- a hairy bed of little physical barriers. And what this caterpillar does in its first hours of life is it doesn't gain any nutrition from feeding on the leaf, but instead, it mows the lawn. It clips those hairs in this circle here. Its dandruff is simply being shed away. It's not nutritious for the caterpillar.
For every defense that the plant mounts in the natural history of co-evolution, there's a counter defense or a counter ploy by the animal. So trichomes, or these leaf hairs, are put forward by the plant. And they're shaved away by the caterpillar. If the caterpillar survives shaving those trichomes, the next barrier to feeding that it faces is really a spectacular and violent defense. It's the latex, that white, sticky emission that you may have seen breaking a milkweed leaf.
This monarch butterfly caterpillar, it shaved its hairs. It took its first few bites. And at the site of damage, a large droplet of latex weld up. It carried the animal down, and it glued it dead to the leaf here. I found this leaf in the field. And not an insubstantial fraction of caterpillars die this way. It's 30% to 60% of them die this way.
And to me, what makes that just so remarkable is this is essentially the only plant that that caterpillar eats. It's not that it happened to lay an egg on a suboptimal thing, and therefore 30% to 60% of them died. This is its only food source, and the plant's doing pretty darn well if it's killing off some large fraction of them at this very early stage, in that first day of life after they hatch.
But in the natural history of co-evolution, every defense that the plant mounts has a counter defense. This is something we call the vein drain. And especially when the caterpillars are larger-- oh, here's a little demo. That's some of the latex that it exudes when the tissue is damaged, whether a leaf or it's a petiole. And especially the larger caterpillars will spend upwards of an hour disarming that latex flow from the plant.
So that caterpillar, it's getting pretty hungry at this point. It's spent a lot of time cutting a trench or cutting a notch in that leaf. Latex can no longer flow to the distal tissues. Eventually, the leaf is going to hang down. The bubble above its head says, oh, very good. It's no more latex flow. And then it might only be 10 minutes that it takes to then voraciously feed on that leaf. So in some senses, it's spending more time, or may spend more time, deactivating the defense than actually eating that leaf.
OK. Now once the caterpillar survives that first day, or two, or three of life-- it's shaved the trichomes, it's drained the latex away-- it now has to contend with both building its body off of eating those leaves in its vegetarian ways. And it also has to deal with the toxins that the plants may have produced that are in those leaves that it's now hungrily consuming.
For the milkweed plant, these toxins are called cardiac glycosides. And I'll talk more about this later, but cardiac refers to the impact of those compounds on our vertebrate or human bodies. And glycoside means that it's a chemical compound that has some sugars associated with it. It's a steroid comp-- and I'll talk more about that in a moment.
In the natural history of co-evolution, every defense is met with some counter adaptation. And this case is no different. The monarch butterfly has genetic mutations-- I won't detail those to you here-- which make it 100 to 200-fold less sensitive to these toxins than the average other animal. The lion's share, 99% of insects and certainly, vertebrates and other animals are highly sensitive to these toxins. But very small changes in the genome of the monarch butterfly have made it largely insensitive.
Now when you have a highly specialized animal that only eats milkweed and is now insensitive to this poison, the next phase in the evolutionary or the co-evolutionary interaction is not only does the animal survive and thrive on this toxic plant, but it packs away those toxins in its own body. And the reason an animal might sequester toxins or pack them away in its own body is that it then protects the animal from its own predators.
The monarch butterfly was famously shown in the late 1950s, largely through the work of Lincoln Brower, to take the toxins from the plant, keep them in the chrysalis phase, and keep them in the adult butterfly phase. They're most concentrated in the wing scales, in the outer parts of the butterfly. Why? Because presumably, the butterfly can afford to lose a little bit of its wings, especially if it causes that bird to feel sick or to taste something bitter.
So what Brower showed in the late 1950s was that a blue jay, if it eats a monarch butterfly that has been feeding on a plant with these cardiac glycosides, in about 12 minutes will puke, will vomit. And this is before my time, but there's all kinds of popular articles about Brower's barfing blue jays.
It turned out to be a very reliable assay-- I don't think you could get away with this so easily today-- but a very reliable assay of the toxicity of the monarchs. And he, again, famously showed that monarchs, that if you could force feed them and work very hard to feed them nontoxic milkweed leaves that don't have toxins in them, then the blue jays were not going to barf. So it really was that toxin that was sequestered away.
OK, what are we doing here? OK. So here's the caterpillar. It's feeding away. Just some quick pictures. What happens after spending 10 days in the caterpillar phase, they enter the J phase. They find a place to hang, often away from the milkweed plant. And I think that's largely to get away from the evidence. And then in about, let's see, 30 minutes, the transformation occurs from the J. The skin is shed.
You can see-- I love this image here because it's just so alien. In that 30 minutes transformation into the-- it's still soft in this case, the pupa, or the chrysalis, that will eventually harden. The spots are initially yellow, and then they harden to be gold. You wait about 10 days. And at the end of that 10 days, the chrysalis turns from the green color to seeing the wings. And it's about 10 minutes until they're fully pumped. Again, this is a pretty soft butterfly that can't yet fly. But it is sort of fully formed there. OK.
OK, good. The next thing I want to tell you-- and I guess it's very important for me personally. It's also important for the story of monarchs and milkweeds to dispel a widely held myth about this butterfly. And that widely held myth is that monarchs are good pollinators. They are not good-- they're certainly not good pollinators of milkweed. And they might move a little bit of pollen around on the goldenrods or the asters in the fall, but they're not doing the lion's share of that work.
And so despite the fact-- I mean, I don't know if-- when President Obama issued the memorandum of pollinator health, there were only two species mentioned by name. And it was Apis mellifera, the honeybee-- hi, Tom-- and Danaus plexippus, the monarch butterfly, which on the one hand, I was thrilled that the monarch was swept up in pollinator conservation and could be a poster child.
But as a scientist at some level, you want to be honest about what the animal is doing. And in this case, the monarch and the milkweed, the butterfly is an antagonist, or an enemy, or an herbivore, or a predator-- whatever word you want to use-- of the milkweed plant. And I thought I would just share with you the reason why that's the case. Go ahead.
ANURAG AGRAWAL: Large Hymenoptera, asks Brian Danforth. [LAUGHS] Pretty indiscriminately-- and I'll show you a picture of a honeybee in a minute. Smaller Hymenoptera are the main pollinators, and I'll tell you why. So this is a pretty big animal. Here's Asclepias tuberosa, or the butterfly weed flower. It's also native to around here, but it's not the common milkweed.
And the way the monarch sits on this flower with its big clumsy body and legs, it never gets into contact with what my colleague at Cortland calls the business end of the flower. The business end of the flower is where the pollen might be removed and then later used to pollinate the plant. And to explain this part of it to you, you need to know that milkweeds are very special in that they share a trait with orchids. And it's the only two groups of plants that don't have their pollen in free-flowing grains the way we think of them, but that package them in what we call pollinia. There are large structures where there's hundreds of pollen grains.
And so instead of dusting the tongue or the body of the butterfly and moving pollen around, the butterfly or the large bees, in this case, must remove the pollen sac from the flower and then insert it into the slit of the female to reach the female part. And the pollen sac is right here. So if we zoom in on this same picture here, it looks like a wishbone. And what a large Hymenoptera would do is get its leg caught here, lift up, and damage some of that floral tissue, but pull out that pollen sac. And then later, through crawling around and drinking the nectar here, would insert one of those ends of the wishbone into the slit, which is right here.
So this is the pollen sac or the pollinia up close, if you remove it from here. And on this bee, you can see it has done a good job drinking nectar, getting a pollinia stuck on its leg, and eventually through will get it inserted. But the way the monarch's body is and the way it sits on the plant, it's simply rarely coming into contact with that part of the plant. And that's pretty cool, and it's always nice to be aligned with orchids in some way. Go ahead.
ANURAG AGRAWAL: Yeah, so when they visit the daisy family in the fall, it's thought that there's unrolling their proboscis, their tongue, and they probably get some pollen on it. But they're probably not the important pollinators of those plants. Yeah. Butterflies in general, I think. Butterfly pollination-- not so much in terms of how important it is. Yeah.
ANURAG AGRAWAL: Advantage is a difficult question for me. I mean, I think it's been a successful strategy for the plants. And well, I think there's all kinds of potential advantages. I think there's a lot less waste, at least. If the pollinia gets inserted, all of those pollen grains are making it to the female part.
An advantage for us as a scientist is that all of the seeds in one fruit, or we call them pods sometimes-- I think the technical term is a follicle-- all of them are full sibs. They share the same mom, and they share the same dad. And normally when you collect the seeds from a fruit of a plant, you know who the mom is because they came from that maternal plant. But the pollen grains are coming potentially from many sources. In this case, it's only one pollinia, pollinium, that gets inserted. And so they are all full sibs or share the same mother and father.
How are we doing? Here we go. How are you doing, Anna? OK, a little bit more the life cycle and natural history of these things. So where are we right now in the annual migratory cycle? We're in April. What's happening? Well, what's happening is the monarchs have arrived in the southern US from over wintering in Mexico. I'll talk more about Mexico in a minute. As of a couple of weeks ago, they were mating, and they had flown to the southern US. And the first generation in the United States were laid on milkweeds in the Gulf states.
And there's basically four generations that happen every summer between April and August, about a month apiece. Eggs are laid, caterpillars are eating, chrysalids are formed, and butterflies are flying. From Texas and the Gulf states, they move north. They'll arrive here in a couple of weeks. It is these four generations-- more or less four months-- let's say between May and August-- when the butterfly intensely and necessarily relies on the milkweed as its host plant. Eggs hatch, they feed, they become adults, and that cycle repeats itself.
But beginning in August-- and all of you know this, but I'll just walk through it with you-- they have their tremendous and spectacular annual migration where they move to the highlands of central Mexico. All reliance on milkweed ceases in mid-August. The plants are no longer in flower, so they're not even drinking nectar from milkweed plants. They're drinking nectar from those Joe Pye weeds, and those goldenrods, and the other plants that are flowering in the fall. They fly there 3,000 to 5,000 kilometers to Mexico, the southern flight. And then they wait there for four months in the highlands of central Mexico. Mating happens, and the cycle starts again.
And I think it's a very important thing for us to think about when we're just having our minds blown by how amazing it is, or when we're thinking about the conservation of these things, that they really have a complex life cycle, where it's all milkweed all the time in the summer, and it's long distance flights, and it's over wintering in these places, and then the cycle starts again.
So very quickly here, we are in Michoacan, bordering the state of Michoacan, bordering the state of Mexico. Above about 10,000 feet of elevation, a very specific forest type that happens to be quite threatened [INAUDIBLE] fir forests, reminiscent of the firs that we have up here, different species that grow at this very high elevation in Mexico. They wait there for four months. They fly here.
Generation two moves up. Generation three and sometimes four spend their time in the Midwest and the Northeast. And then in August, September, and October, they fly south again. The populations on the east side of the Appalachians are somewhat distinct, not genetically, but they kind of bifurcate from the Gulf states going east of the Appalachians or not. And so often, when we're studying these things, we think about the Midwestern versus the Eastern population.
In general, we normally see monarchs as being relatively dispersed here in the Northeast. In the summertime, they might be flitting around. But beginning in the fall-- this picture was taken in September in southern Ontario-- they begin to cluster, and they roost overnight on trees. They only fly during the day. And so here in Southern Ontario in September, they're beginning to congregate in that last generation. And further on in the evening-- I don't think I put in this picture-- there'd be hundreds, if not more, on individual trees. And then they make that flight, maybe 50 miles a day, during the day.
ANURAG AGRAWAL: It's third or fourth, basically. And that depends on kind of how quickly the season gets started, growing conditions during the season. And probably some of you have noticed this, we often have a-- I like to refer to them as the living dead-- a generation that doesn't quite make it. In October, [INAUDIBLE] caterpillars in October but they're not going to, even if they pupate-- they're sensitive to frost-- but even if they turned into a chrysalis, they're not going to eventually make it to Mexico. Yep.
And it's really great. People have worked on the various cues that cause them to change their behavior. They don't mature their reproductive organs, and then they turn south and they start flying. And it has to do with day length, temperature, and also the senescence of the milkweed plants at the end of the summer.
So this image was taken from Michoacan from the overwintering sites. On warm days, they take to the air. They go to streams to drink water. There really aren't a lot of flowering plants then at that time of the year there at that elevation. So the other thing which I guess I failed to mention is, once they become a butterfly in August and September, the only food that's sustaining them for the next-- whatever it is-- seven or eight months is floral nectar and water. And the floral nectar, again, is not from milkweed plants. So they're flying down there, and then on the warm days, they're going stream side to drink some water.
Here, they literally weigh down the trees. So these what looks perhaps like brown dead leaves, like we might see on a beach or an oak tree outside here, are butterflies. If you look up at the sky, it really is a magic-- I sort of read all about it, and when I went in 2012, it blew my mind. It's just really a great-- they're just coating the branches.
And this is image of Lincoln Browers from an airplane at the overwintering roost. And they're often associated with these prairie areas that are called [INAUDIBLE]. The red or the orange that you see here is clustered butterflies. I mean, it's just unbelievable, right? In the last couple of years, there's been in the 100 or 200 million butterflies. In the biggest of years when the butterflies have been more abundant, it's upwards of a billion butterflies. And they all cluster-- I'll show you this image in a little bit-- they all cluster on about 12 mountaintops. A very restricted area, so they're very concentrated in Mexico.
How are you guys doing? You have questions?
ANURAG AGRAWAL: Have a tougher plant to chew, yes. Yep. Go ahead.
ANURAG AGRAWAL: Yes, so here is the thing that is really amazing. So during the summer months, egg to egg-- meaning egg that turns into a caterpillar, turns into an adult, mates and lays another egg-- that generation is four to five weeks. And the butterfly is not living a couple of weeks as an adult, and then it's done. That last generation, number four, lives for eight months, the butterfly does. So generations one, two, and three complete it and are kaput. And that last one-- yeah. Go ahead.
ANURAG AGRAWAL: As an adult. As an adult butterfly, they're drinking nectar. So the adult butterfly has a tube like mouth part, and it can only get liquids. So especially in the spring, they are frequently drinking milkweed nectar. Because they're there in the places they want to lay eggs. And nectar from other plants, but that's what they're eating. Yeah.
ANURAG AGRAWAL: That's a good question. The clustering is thought-- so there is some heat thing going on. And not only do they cluster together, but they cluster in particular parts of the tree. And the trees are radiating heat back. I assume there's a predator thing-- a predator satiation or a predator avoidance thing by clustering. Yeah. But I mean, I would say I don't fully understand that. And on the southern flight down, again, they're roosting commonly on individual trees. And I guess that that, again, is about predation, or yeah. Go ahead.
ANURAG AGRAWAL: I can help you with that. It's a little bit of a longer discussion, but I agree that they're not super easy to germinate. And I prefer to grow them, if possible, indoors or in a window or whatever for a couple of weeks, get them established, and then they transplant really, really well. So--
ANURAG AGRAWAL: Yes. And they like-- yeah.
ANURAG AGRAWAL: Yeah. But I can talk to you more about that afterwards. There's some tricks. Yeah.
ANURAG AGRAWAL: They like to be wet and cold. I mean, they like to experience a winter, basically. Yeah, go ahead.
ANURAG AGRAWAL: The navigation is mind blowing. So there were various hypotheses out there for a while about how they do it. It turns out they use what's called a time compensated sun compass. And the way to think about that is that if you look at the sun at noon, especially at the time when they're migrating, the sun is more or less south. And if they're trying to go more or less south, you think you might be able to use the sun as your navigation means.
But at 10:00 in the morning when you start flying and at 4 o'clock in the evening when you're done flying, following the sun is going to screw you up. You're going to be flying more or less east in the morning and west in the afternoon. So their internal clock, their circadian clock, which all biological organisms have, compensates for their use of the sun. And the experiments were just spectacular, right? What they did was they trained the monarch butterflies on a daylight cycle that was six hours advanced or six hour delayed.
And what the researchers-- so it's not my own work-- showed is that in the morning, they fly with the sun on their-- see if I can get this right-- expecting the sun to be to their east, so that they can actually-- they fly with the sun in the right position to go south. And that's reversed in the afternoon. So basically, there are various simple experiments cutting off the antennae or whatever the-- the clock mechanism is, in part, in the antennae. Yeah, really fabulous stuff. And other animals use the time compensated sun compass as well. It's still not clear. So that's their compass, and for any organism that migrates, you need a compass and a map. And it's still not clear what their map is.
ANURAG AGRAWAL: Now they have not been there before. So unlike most vertebrate migrations, birds and mammals, individuals make the round trip. But right here in this case, generation four is flying down and makes it back to Texas. And then it's one two and three. Yeah, so for a while, it's thought that it was the Earth's magnetic fields was providing the map, and that's been shown for sea turtles and some birds, that you can put them in these chambers with altered magnetic fields, and they think they're in Australia or whatever.
It doesn't seem that the monarch is using a map based on electromagnetic fields. Three times, people have tried FedEx-ing monarchs to other parts of the country to ask if they'll fly the right direction, or they'll adjust themselves. And it's kind of been inconclusive for various reasons. Go ahead.
ANURAG AGRAWAL: We have a website.
ANURAG AGRAWAL: Sure. Yeah. And there are many websites on propagating milkweed. I mean, I could certainly just direct people to the-- yeah. No, that's a great idea. I like that idea. Go ahead.
ANURAG AGRAWAL: I'll tell you the one thing you don't do is you don't till the field. Because that chops up the rhizomes, and it kind of spreads them.
ANURAG AGRAWAL: They can be very deep. Roundup works pretty well. Yeah.
Yeah, so here we are. I'm not going to give you the rest of this talk, but let's talk about cultural history just for a moment. Because it is pretty amazing stuff. It's very different than what we've been talking about. So milkweeds, the family is, in part, characterized by having these cardiac glycosides. This is the chemical structure right here-- not very important. There's lots of diversity within the genus that these plants come from. I just show you some of the floral diversity here.
And if you think about the plant kingdom as it were, the 350,000 species of plants, flowering plants, that have been identified, the lion's share of them that have these toxins are in this family. 90 probably some percent of the plants that have these toxins are in this family. But there are a few others that have independently evolved cardiac glycosides. So fox glove, a common garden plant, is one that makes cardiac glycosides also. And there's some lilies that make cardiac glycosides also.
And if you go back into thousands of years into the past, a truly remarkable convergence occurred both on a plant evolution scale and a human cultural scale. So Native Americans, North Africans, and Romans-- that's what that's supposed to be-- were all using cardiac glycosides to treat congestive heart failure. They didn't know what the compounds were, and they were in different groups of plants. The milkweeds were being used. Squill was being used. Foxglove Digitalis was being used to treat congestive heart failure.
Now there's one group of animals that also produces cardiac glycosides, and it's the toads. And in China, secretions from toads were also being used to treat congestive heart failure in their history. So I mean, I don't know. There's not much more to say about it than to simply marvel at the convergence in how-- who were the experiments done on where we were looking for the plants that made these compounds to treat these maladies.
But moving forward, in the late 1700s, Charles Darwin's grandfather, who was a great botanist, but also a medical doctor, was very into prescribing foxglove to treat congestive heart failure. There was beginning to be sort of accumulation of scientific data that extracts of these plants were useful in this way. They helped relieve what was often called dropsy, which is the accumulation of liquids, of water in extremities due to the poor pumping of the heart.
Now as all of you know, dose makes the poison. And what I mean by that is that small amounts of these toxins can be very beneficial to us, in the way that we might put chili pepper on our pizza. Or the same compounds can be used in pepper spray in the case of chili pepper. Or in the case of cardiac glycosides, the Romans used foxglove extracts both as a rat poison and also to treat congestive heart failure. Dose was absolutely critical in the effects that one might see.
I want to fast forward to 1981, thinking about dose of cardiac glycosides to share with you something that was a medical hypothesis about these toxins that milkweeds have that a medical doctor published in the Journal of the American Medical Association. That's the February 20 issue of 1981. And I don't normally like to do this, but it's just so well-written, I want to read with you the abstract of this paper from JAMA in 1981. It's about Vincent van Gogh. This is Dr. Gachet, his famous painting. He painted his doctor twice.
"Vincent van Gogh, the Dutch postimpressionist painter, died in 1890. He was an uncommon man. Auto-mutilation, depression, insanity, and suicide are all part of his medical history. During the last two years of his life, his paintings were characterized by halos and the color yellow." If you actually look into it, it's pretty distinct transition. You know the sunflowers and starry night.
"Van Gogh was likely under the influence of digitalis intoxication. This hypothesis is based in his twice having painted his physician holding a foxglove plant that this medicine was used in the latter part of the 19th century in the treatment of epilepsy and that the toxic effects of digitalis may have, in part, dictated this artist's technique."
And it's just unbelievable. This guy was overdosed with digitalis, with cardiac glycosides because they didn't know what to do with him, basically. He did suffer from epilepsy, but I think he also had so many other problems. They were doing the experiments not intentionally in a negative way, but they were giving van Gogh this stuff. And the foxglove tea likely shaped how he saw the world in those last two years before he died.
I want to just tell you the last thing about cultural history is that actually, around 1981, the same time when this medical hypothesis was put forward, there were physicians trying to study the causes or the survival rates of breast cancer patients. And they accumulated 1,000 studies, 1,000 cases of individuals that had breast cancer, and asked the question, can we predict what made some of them survive better than others?
And as it turned out in this-- we call this a meta analysis now in science-- but this retrospective look at 1,000 cases in the late 1970s, early '80s showed that the highest survival rate in that set of 1,000 cases were those patients that were also taking digitalis for congestive heart failure. And that led to the hypothesis that these compounds-- it's just a hypothesis, it was an association at that point-- that may have anti-cancer properties.
And so between 1981 and now, or 1980 and now, in the intervening decades, there's been further, and further, and further study, both in test tubes and what we see now are clinical trials, where cardiac glycosides, in the right dose and with the right chemical structure, are being administered to assess the impacts on suppressing cancer in humans. So what an amazing chemical compound, or set of chemical compounds, in that they have all of these effects.
Can I ask a question? Should I stop now? I mean, it seems like it's-- and I guess I want to ask not the audience, but the people in charge. Is it like--
MARY OCHS: [INAUDIBLE]
ANURAG AGRAWAL: My time is up, OK.
MARY OCHS: No, no, no. [INAUDIBLE]
ANURAG AGRAWAL: Oh, here we go. I'll talk for five more minutes. OK, here we go. Feel free to leave. Conservation, so monarchs are in the news. We're worried about them. That's, I think, for good reason. I want to tell you just briefly about how the conservation sort of story came about, how we were able to understand that we should care about monarch conservation. And it's kind of interesting because it actually makes me think there's good reason to be a biologist, and even a basic biologist.
We weren't, as a group of scientists or as a society, able to think about monarch conservation until we understood their life cycle. And quite remarkably, we didn't understand their lifecycle until the mid 1970s. It was really when, at least, American science-- it's clear that native people in Mexico and the highlands of Michoacan knew about monarch butterflies overwintering. They just weren't sharing that information with American science.
But it wasn't until scientists discovered those overwintering sites and understood the lifecycle that conservation really became a concern. And the back story is that as early as the late 1800s, butterfly enthusiast entomologists knew that in the fall, monarchs were flying south. In fact, the Comstocks that were the founders of the first entomology department in the country here at Cornell, in their book on butterflies, basically got the story right. 1897, monarchs fly south in the fall. They overwinter somewhere. They didn't know where. And then they migrate north in the spring.
What Fred and Nora Urquhart started in the 1940s was a program to try to understand where the heck they went. And they started with tagging, putting a little hole punch size, or a little bit bigger than hole pint size, tags on monarch butterfly wings in the fall that said, if you find this, please send it back to the Royal Ontario Museum in Toronto. And between 1952 and 1955, they started, basically, the first real citizen science movement to answer a very specific scientific question. Where do they go in the winter?
There were 200 people between 1952 and 1955 across the US and Canada that were tagging and sending them back. But with the scale of this thing, you don't answer the question with 200 people. By 1970, there were thousands-- a couple thousand people-- that were tagging and returning these things. Urquhart had a sabbatical in Texas, and he realized-- his hypothesis was they kind of hung around Texas, and maybe made their away to California and made their way back. But he kind of realized that that wasn't what was happening. They were going into Mexico.
He published newspaper articles in Mexico City asking for help, putting ads in papers, getting help with translation from Spanish to English and English to Spanish. And basically in 1975-- 30 years after they started tagging butterflies and really generating a movement of people, citizen scientists engaged in trying to help-- did they find the overwintering sites in the highlands of central Mexico.
And it wasn't announced on Twitter. It wasn't even announced on the evening news. It was announced in the August 1976 issue of National Geographic. It's unbelievable, right? So one of the two citizen scientists here, Catalina Trail, was featured on the cover of National Geographic. And it was an international sensation, right? I mean, found at last. I don't want to tell you in the last couple of minutes. I have to skip this story. It really is a great story.
But once the life cycle was complete, and people understood that the monarch butterflies overwinter-- all 200 million to 1 billion-- overwinter in a small area the size of New York City on 12 mountaintops in Mexico, once that lifecycle was pieced together did people understand the fragility of this cycle. Without these 12 mountaintops, it's unclear what happens to monarchs in those four months when they overwinter.
And almost immediately-- there were all kinds of scientific discussions, and debates, and controversies-- but almost immediately, the conservation discussion began. And it began with discussions about logging at the overwintering grounds, which continues. Climate change did not really creep into the discussion until the '80s, but it did then. Habitat loss, insecticides and GMOs, herbicides, which are chemicals that are not killing the monarchs directly, but are killing plants, milkweeds, in farm fields that may be responsible for reducing their populations. Big winter storms can result in literally tens, if not hundreds, of millions of monarchs falling off trees, many of which die.
And the picture any way you slice it is not good. Here's 20 years of data. Here's an estimate of the size of the overwintering population of monarchs in Mexico. It's measured not by counting all 200 million, but it's measured by assessing the area of densely occupied forest. Hectares is the metric version of acre. It's an area of occupied.
And since 1992, I used to think that if I just covered up this one data point, it wouldn't be a negative relationship. But it's negative. You can't do anything to this. The worst years were 2011 to 2014-- worst years in history. They correspond to the greatest drought that the southern US, the Gulf states, and Texas has seen in 50 to 100 years. Once that drought broke, we saw a doubling in the first year, and then a tripling in the next year. And this past winter, basically, they were a little bit down from the previous year. But they're sort of what I call in, let's say, stable dangerous zone. This is, I assume, year to year fluctuations that we have seen in the last year.
There's a national agenda to plant milkweed. When I wear the milkweed shirt in the grocery store, people tell me they're planting milkweed, and I say, awesome. Plant native milkweeds. Michelle Obama planted some milkweed-- not these plants-- but in their kitchen garden. It's a non-edible, but in their kitchen garden. I'll just end with saying that our own research in my lab-- and a lot of that was conducted by [INAUDIBLE] who's here in the audience today-- suggests that milkweed is not what's limiting the monarch butterfly's population and is not what's causing it to decline.
Getting to and establishing at the overwintering sites in Mexico seems to be the break in the cycle. We don't know what the cause is. It could be many things. They need that nectar to fuel their thousands of kilometers of light. They certainly are susceptible to insecticides not only in lethal doses, but remember, dose makes the poison. Sub lethal doses of insecticides, I think, are one of the most insidious ways that chemicals can impact organisms, simply making them sick or weak. But if we count the numbers, the numbers may not be declining at that particular stage.
The last 800 miles when they get to Texas through the overwintering sites, when they get to the border with Mexico, virtually unknown. And it's got to be the most difficult in terms of it's the end of the journey, very, very dry habitats. And then continued degradation at the overwintering grounds is where our hypotheses are. So with that, thanks a lot for listening. And we can have more questions. I'm happy to sign a couple books. And thank you.
SPEAKER: This has been a production of Cornell University Library.
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Known for their bright colors and epic annual migration from the United States and Canada to Mexico, monarch butterflies are beautiful but complicated creatures of nature. In his new book, Cornell professor of ecology and evolutionary biology Anurag Agrawal presents a detailed investigation into the complex co-evolution occurring between the monarch and the incredibly toxic milkweed.
The inextricable and intimate relationship between the monarch butterfly and the milkweed plant has been like an arms race over the millennia. Each spring, the monarch life cycle begins when it deposits eggs on the leaves. Even though the plants do all they can to poison the predators, the larvae appear to feed exclusively on them. The milky sap poisons contained in leaves and stems have not only shaped monarch-milkweed interactions but have been culturally important for centuries.
In an April 2017 Chats in the Stacks book talk at Mann Library, Agrawal discussed his recent scientific discoveries that reveal a battle of exploitation and defense between these two fascinating species. He also reviewed some of the current thinking as regarding the recent decline in monarch populations, the influence of habitat destruction, and his own theories as to why their numbers are plummeting.