Beware of Generalizations: A Pollination Story

Botanists teach that wind-pollinated plants produce lots of pollen and do not bother with nectar or pretty petals. Nectar and pretty petals attract bees, which carry pollen efficiently between one flower and another. Wind-pollinated flowers, however, produce lots of pollen and let the wind carry it. That’s the story. That’s what everybody teaches (I did) you will find in every book (including mine). And, in general, it is true.

But keep your eyes open for exceptions to the rule. I was out for a hike, not expecting to see anything out of the ordinary. But I kept my eyes open. This is what I saw:

This ragweed (Ambrosia trifida) produces lots of pollen, but no nectar or colorful petals. Bees are not as stupid as we sometimes think. This honeybee found the pollen, without needing to be attracted to the flowers. She started stuffing as much pollen as possible in her pollen buckets. She probably went back to the nest to deposit bee bread, but no nectar.

I assumed that I could tell what pollinates a flower by just looking at it. If animals such as bees pollinate it, it should have colorful petals. Consider willows. Even though the male flowers have very inconspicuous petals, they have big anthers full of pollen. The female flowers also have very inconspicuous petals. I assumed willows were wind pollinated. But it turns out that the flowers have nectar, and bees can smell it. It is bees that pollinate willows.

Close and repeated observations reveal the truths of nature. Quick glances and generalizations do not.

In the next essay, I will tell a story about another generalization, involving leaves and photosynthesis, which turns out to have exceptions.

A New Look at Orchids

In an ongoing and apparently permanent glitch, YouTube does not provide links to videos that have been uploaded. Here is a current list of my Darwin YouTube videos that have been posted but do not get publicized:

Hidden Lives of Plants Toxins Await You [https://youtu.be/ObZHJYVfw-E]

Hidden Lives of Plants A New Look at Orchids [https://youtu.be/LcwL_pDxX2E]

I wish to tell you about the second one, about orchids. The URL is indicated above.

Most people see orchids as amazingly beautiful flowers. Many people are utterly captivated by them. They are, in a way, the dinosaurs of the plant world, except that they are not (yet) extinct.

But we can also see them as amazing examples of plant evolutionary success. As explained in a previous video, plants are engaged in a continuous, silent struggle for not just survival but evolutionary fitness. Everything a plant does with its resources, the food it gets from photosynthesis, must be efficient. Every part of a plant must pay its own way. If a plant invests its resources in a process or organ that does not pay for itself, it risks extinction just as surely as if it fails to invest in something essential. The silent struggle of plants is more like a marketplace than a battlefield. In the previous essay I explained that flowers have to pay for themselves.

Orchids are an amazing example of extreme plant adaptation to success in the marketplace of plant competition. First, consider the flowers. They are really big in comparison to the rest of the plant. They represent a big expenditure. They had better be successful in attracting pollinators, or else the plant has wasted a lot of energy for nothing. Orchids live up in the branches of tropical rainforest trees (they are epiphytes). They are scattered far apart from one another. The flowers have to be big and showy to attract their pollinators from a great distance. Also, they are very complex, so that only the correct pollinators, the ones most likely to visit another orchid of the same species, can pollinate them.

Epiphytic orchids also have succulent leaves. Though it may rain every day in the rainforest, it gets hot and dry between the rains. An epiphyte, with its roots hanging out in the air, can quickly dry out unless it has some adaptation, such as succulent leaves, to slow down its water loss.

The roots stick out in the air. Since they absorb rain, they do not have tiny root hairs. But since they are in the air, not the ground, they absorb sunlight. This is an opportunity for the orchid plant to get in a little extra photosynthesis. Epiphytic orchid roots are green!

I am working on a book, tentatively entitled Silent Struggle: The Hidden World of Plants. Watch for it!

Flowers: They Aren't Just Pretty

I have posted a new video in the series Silent Struggle of Plants: Flowers, TheyAren’t Just Pretty.

In this video, we take a close look at a trumpet creeper flower (Campsis radicans), an abundant summertime vine in much of the United States. It is certainly a pretty flower. But flowers have to pay for themselves, or else the plant loses its investment in the marketplace of evolutionary struggle, as explained in the previous essay. A plant that spends too much on its flowers faces extinction as surely as a plant that spends too little.

In particular, a flower has to be a successful advertisement to pollinators. The trumpet creeper uses its bright red color to attract hummingbirds from far away, and offers a reward of pollen and nectar at the bottom of a long tube that is perfectly suited to the hummingbird’s long bill. (Of course, no hummingbirds dared to visit during this video.) Other pollinators tend to ignore trumpet creepers; bees, for example, cannot see red, and they tend to not notice these flowers.

I hope to show in this video—and in the next one also—that flowers aren’t just pretty, but are an investment in successful reproduction. A plant cannot afford to produce showy, but useless, flowers.

I am working on a book, tentatively entitled Silent Struggle: The Hidden World of Plants. Watch for it!

It Isn’t Pretty, It’s Ecology

Sometimes we like to think that the natural world is all full of nice animals and plants just waiting to be explored by day hikers like me. We all know this is not true, but it is a nice feeling. On the other hand, certainly in the world of bees and flowers, the world must be pretty nice, right?

It would be nice if pollinators and flowers just helped one another out: the pollinators get pollen and nectar as food, while the flowers get to cross-breed and enhance their genetic diversity. But the reality can be pretty messy. Pollinators do not just need resources, but they need to be the first pollinators to get those resources. The first pollinator to visit the flower gets the nectar, which may or may not be replenished by the time the second pollinator arrives. With this kind of competition, some pollinators may not even wait for the flowers to open. They might chew a hole through the petals to get at the nectar in an unopened flower. In so doing, they do not pollinate the flower, since they do not brush up against either the stamens (which produce pollen) or the stigmas (which receive it). These insects are just like the Sooners in Oklahoma history, who sneaked into Oklahoma Territory to stake out their land claims before the official opening shot.

Not only that, but flowers are specialized for certain pollinators. Wisteria flowers, for example, have petals in the form of a banner, wings, and keel. The pollen and nectar are down inside the keel. The keel is closed up, and only a fairly heavy pollinator, such as a bumblebee, can open it. Honeybees cannot easily open them.

When I walked home from work one recent afternoon, I saw honeybees flying around newly opened Wisteria flowers. Usually I see bumblebees, but this does not seem to have been a good year for them. But why were the honeybees there? It turned out that the honeybees were chewing holes in the side of the flower to drink the nectar down inside, as in these photos.

Mother Nature can be one tough mama. Snakes eat cute little nestlings, parasites are everywhere, and even when bees visit flowers there is a Darwinian struggle for existence going on. Of course, I feel a sense of awe when I behold the overall structure of nature.

Evolution 2011: Evolution is Alive and Well

I have just returned from the Evolution 2011 meetings in Norman, Oklahoma. This is the pre-eminent meeting of evolutionary scientists in the world, sponsored by the Society for the Study of Evolution, the American Society of Naturalists, and the Society for Systematic Biology. Anyone who thinks that evolutionary science is based on very little evidence should experience the flood of data reported at the Evolution meetings every year. All over the world and in every group of organisms, the evidence continues to pour in that evolution is occurring all around us and has been occurring for billions of years. Those of us who have been around longer took special effort to encourage the graduate students and postdocs who have done amazing and creative research.

I will briefly mention three of the graduate student papers that I found particularly interesting.

Sarah Ann Bodbyl Roels (University of Kansas) conducted an experiment in which bees selected floral traits in a monkeyflower species for several generations. Both the treatment and control were inside of identical greenhouses, with the bumblebee hive inside one of the greenhouses. This is a particularly good example of experimental design.

Carolina Bonin (Scripps Institute, La Jolla) obtained DNA samples from seals near Antarctica to determine patterns of paternity in a population that had been driven nearly to extinction. Getting DNA from a male seal is not an easy task; you have to run up with a sample vial on a pole, poke the male to get a blood sample, and run like hell as the male flops along after you. Impressive work.

I was most impressed with the work of Kelsey Byers (University of Washington), who has figured out which chemicals stimulate the bumblebees that pollinate monkeyflowers. She did this by inserting electrodes into the exposed brains of bumblebees, and measuring electrical stimulation in response to different volatile chemical components of nectar. This is a very creative approach to the study of pollination.

The meeting was also an opportunity for people from all over the world to talk about what is happening on the creation/evolution front. Oklahoma is perhaps the world epicenter of creationism, and visitors from other countries wanted to know what is going on here. In the photograph, Vic Hutchison (the grand old man of evolution education in Oklahoma) talked with foreign students Bjorn Ostman (originally from Denmark) and Olga Dolgova (originally from Vladivostok, Siberia) about the evolutionary political scene in America.

Organizing this meeting and making sure that everything happened on time for the hundreds of participants was a big job, and I want to thank Rich Broughton, Larry Weider, and Ingo Schlupp, all faculty members at the University of Oklahoma, for their amazing work in making this meeting a success.

I will post two more entries about the Evolution 2011 meetings.

I am the author of Life of Earth: Portrait of a Beautiful, Middle-Aged, Stressed-Out World, recently published by Prometheus Books. See my website for more information.