New Video: Darwin Eats Tree Leaves

In this video, Darwin jumps around in springtime exuberance and eats leaves of a water oak (Quercus nigra). He was inspired to do this by seeing a French video in which a naturalist ran around in the French woodlands and ate young leaves. He smiled really big and talked about how good they were, including oaks, willows, poplars, beeches, etc.

But the French videographer warned his viewers that they should do this only with very young leaves. Older leaves in European forests are full of toxic compounds which, although they will not kill you, at least taste bad. The leaves manufacture these compounds (for example tannins) to discourage animals, especially caterpillars, from eating them.

But it can be expensive for a leaf to defend itself. Every molecule of defensive chemical that the leaf makes has a construction cost in energy and raw materials. These costs could be used to make more leaf area, which is an investment in photosynthesis that will bring in more energy and raw materials. The ideal amount of defense spending for a leaf (or a nation) is zero, but this is not possible in a dangerous world. Therefore, leaves, like nations, economize their defense spending. Leaves make defensive chemicals only when they are needed.

Ever since the work of Paul Feeney fifty years ago, scientists have understood that, in European forests, many herbivorous insects die during the cold winters. Their populations build back up during the warm, wet summers. The forest trees, such as the oaks studied by Feeney, economize their defense spending by producing very few defensive compounds in the spring, then more and more as the summer goes on. In the early spring, therefore, the forest is almost like a big salad bowl, especially for the Frenchman I mentioned earlier. In the video, Darwin decides to eat a young water oak leaf in Oklahoma.

Darwin got a surprise. The leaf was bitter. Then he understood why. In Oklahoma, the winters are not very cold (February 2021 being a significant exception) and many insects can find little crevices to hide in. In Oklahoma in the spring, unlike in Europe, the insects can come out in full force. The young leaves are ready for them, having defended themselves with chemicals. Many of the insects die during the long, hot, dry summers in Oklahoma; that is, their populations die back in the summer, not so much in the winter.

This raises the possibility that tannin concentrations in Oklahoma oaks are high in the spring and lower in the summer. Of course, once the leaf produces tannins, why not just keep them all summer? But it is possible that the tannins can be degraded and the molecules used for something else. I tried to measure this in post oaks (Q. stellata), only to discover that I am not a very good chemist and failed to measure the tannin levels correctly.

I did try a different, creative approach to determining whether the early season oak leaves were more toxic than the late season leaves. I ground up leaves in liquid nitrogen and mixed them up into hornworm chow. You read that correctly. Hornworm chow. It turns out you can buy hornworm eggsand caterpillars, and even chow and growth vials, from Carolina Biological Supply. Wild hornworms usually eat tomato leaves, but these caterpillars eat chow, and, apparently, almost anything you mix into it, like leaf powder. The hornworms grew best on the chow. But they grew bigger and faster when they ate late-season oak leaf powder than early-season powder.

So my advice to Darwin is, if you want to eat tree leaves in the spring, go to Europe.

What's Up with the Stupid Magnolias?

What’s Up with the Stupid Magnolias?

In late September, I saw several magnolia trees blooming in Durant, Oklahoma. Magnolias are supposed to bloom in late spring! What’s up with that?

The reason the magnolias bloomed is because they are stupid. Plants are stupid. I say this even though I am a botanist and have devoted my life to studying them. These magnolias, you see, have no idea what time of year it is. They don’t know the difference between May and September.

Yet, they have to bloom at the right time of year, don’t they? Of course they do. They have to bloom at the time that their pollinators are expecting them to bloom, so that the huge white flowers and sultry lemon scent will not be wasted.

But intelligence is expensive. Brains are expensive. Your brain uses twenty percent of your body’s metabolic energy and oxygen. My granddaughter Léna’s brain uses half of her energy and oxygen. That doesn’t make her smarter than you, but it does mean her brain is rapidly growing. Plants simply cannot afford to make brains. For the last billion years, plants and their evolutionary ancestors have relied on more direct stimuli from the environment to tell them when to do things such as reproduce.

To a plant, there is no difference between cold and drought. They do not have temperature sensors. To them, it is cold when the water freezes, and when the water freezes, it diffuses out of the cells and into intercellular spaces, where the ice crystals cannot harm the cell. That is, when it freezes, plant cells become drier. In spring the ice melts and the water diffuses back into the cells.

This summer in Oklahoma had some long periods of hot dry conditions. They were not record-setting, but they were pretty brutal. Then, in late summer and early fall, it rained a lot, and kept raining. Therefore, during mid-summer, the plant cells dried out, and in late summer, they became moist. For anything that the plant knew to the contrary, the summer drought was winter, and the fall rains were spring.

Plant responses to seasons are not the most intelligent ones, but they are economical. Every few years, the magnolia trees waste a few flowers by blooming in the fall; in the ensuing winter, they cannot develop their fruits. But any magnolia would tell you that its way of adjusting to the seasons doesn’t cost as much as your brain does, thank you very much.

Reality of Global Warming: The Phenology 2012 Conference

I am in Milwaukee, where the Phenology 2012 conference has just ended, except for a field trip to a bog tomorrow. It is a small but powerful conference, with scientists and science students from 21 countries. It is one of the most remarkable conferences I have attended. Thanks go to Mark Schwartz at the University of Wisconsin at Milwaukee, who has been one of the world leaders in phenology research for decades—his hard work made this conference a success in every detail.

Phenology is the study of seasonal patterns of organisms: buds bursting in spring, leaves falling in autumn, animals migrating, etc. This is part of the adaptations that organisms have: they have physiological mechanisms that allow them to do the right things at the right times.

Phenology is not only an international science but an interdisciplinary one. Some of the conference participants study satellite data, which show “greening-up” occurring earlier each year, while others study organisms directly. The interdisciplinary nature of the subject is also what has made this a remarkable conference. We also heard from scientists who specialize in citizen science: they coordinate the efforts of ordinary citizens to collect seasonal data about plants and animals, and put these data into an organized database (see the USA National Phenology Network). We heard from educators who involve the public in phenology awareness.

I gave a presentation in which I documented that the Oklahoma trees I have been watching for the last seven years are, in most cases, opening their buds one to two days earlier each spring, which demonstrates a remarkable rate of global warming. The one exception is silver maples, which (in my sample) all died in the 2011 heat wave. This rate cannot continue; if winters become too warm, the buds will actually open later, not earlier, because cold weather is required to break down their inhibitors (inhibitors are sort of like hibernation hormones).

A couple of years ago, Senator Jim Inhofe from my state of Oklahoma issued a list of climate scientists who should be investigated by the Department of Justice for possible criminal activity because they study global warming at taxpayer expense. Since global warming cannot be happening, Inhofe reasons, these scientists must be making stuff up. One of the scientists on Inhofe’s list is Thomas Karl, our keynote speaker, who did not know he was on the list until I told him. Way to go, Oklahoma. But I think all of us who study phenology should also be on the list. (Technically, I would not be on the list, because I have never received funding for my phenology studies.) I began my talk, “Dear fellow criminals…” That got their attention.

I met two scientists (Steven Running and Kirsten DeBuers) who fully accept global warming, but who wrote a paper that indicated that some trees (up in the mountains) would grow more under warmer temperatures. A global-warming-denial website put them on the list of 3000 “scientists who deny global warming.” So don’t believe these lists, folks! Many of the scientists on these lists were put there falsely!

I also met the woman who blogs about global warming for Huffington Post. You can follow her on Twitter at @climategeek.

What does this topic have to do with evolution, the usual topic of this blog? In the past, normal ecological and evolutionary processes allowed organisms to respond to global climate changes because these changes occurred slowly. Organisms could, over the course of thousands of years, migrate: birds could fly, mammals could run, and seeds could be carried by animals or wind. Over the course of millions of years, organisms could evolve in response to climate changes, such as the spread of grasslands about thirty million years ago. But global climate changes, as great as almost any of those, are occurring today over the course of decades and centuries, too fast for either migration or evolution to adjust. In addition, today, there are roads, cities, and farms in the way. If the ocean rises you can’t just move inland—somebody else already owns the land there. Phenology, therefore, is an important field of study. It shows us that the current rapid rate of global warming is causing remarkable changes in the seasonal activities of organisms. These changes serve as a warning to us about what is going to happen, imminently, in our future.

Back in the days of Gilbert White, phenology was a pleasantly peaceful science. White wrote about the arrival and departure of birds, the opening of buds, and the emergence from hibernation of his female turtle Timothy. Phenology did not rock the world the way evolution did. This is no longer true. Scientists all over the world are documenting that plants and animals are responding to global warming. Ordinary people cannot see carbon dioxide. But they can see that buds that used to always open in April are now opening in March, and doing so nearly every year. They are telling us that global warming is occurring, however much Senator Inhofe insists that it is not.