Darwin Didn’t Solve It All

This is the first of an occasional series called “What Do You Do?” in which Tufts Now highlights different members of our university community.

Earth is the only planet in the universe that harbors life—as far as we know—and the sheer diversity of that life is astonishing. Scientists estimate that in addition to legions of single-celled life forms, including bacteria, our planet is home to about 10 million different types of multicellular creatures. How did we come by such an embarrassment of riches? That’s what Tufts biologist Erik B. Dopman, who focuses on evolution and the genetics of natural populations, is trying to find out. By studying one species as it becomes two, he is looking for new clues to one of biology’s oldest and most important riddles—the origin of species.

Tufts Now: Darwin published Origin of Species in 1859. What is there left to know about evolution?

Erik Dopman: There still are very fundamental problems, fundamental questions and gaps in our understanding that demand an explanation. For example, why is it there is not only one kind of species that populates Earth? Why are there thousands of species of microbes in a teaspoon of soil? Why are there more species in the tropics and fewer as you head north or south?

But we’re not just interested in the why. We’re also interested in how separate species occur. Are there certain traits that may predispose one species to split into two or traits that may predispose some lineages towards extinction? Can we identify traits that are diagnostic and thus predict extinction?

Why is this kind of work important?

Well, speciation is a fundamental problem for biology, but my favorite beast warrants concern for other reasons. My current model for studying the evolution of species is the European corn borer. If you’ve ever had a caterpillar in an organic ear of corn from the farmers’ market, it’s probably this one. It causes $1 billion to $2 billion in crop damage in the United States each year. It’s also in Canada, Europe, North Africa and Central Asia.

It’s primarily a pest of corn, but it also eats things you wouldn’t expect, like peppers, potatoes, cotton. So it’s a generalist, and it’s also in the process of splitting into two species. It turns out that the traits that drive speciation also make it a pest. For example, one lineage has a single generation in the middle of the summer. The other has two generations, one in early summer and one in late summer. That difference means the two lineages mate at different times of the year, which encourages the two lineages to diverge. It also means more generations per year, and that makes the pests more problematic. So the idea is that there could be broad societal benefits by addressing fundamental biological issues in this organism. 

What are those fundamental issues?

While they are visually indistinguishable, the two strains that we study reproduce at different times of the season but in the same geographic location. That’s one form of reproductive isolation—one trait that prevents the random exchange of genes.

Certainly geographic distance is another factor that plays a role in speciation, but that’s less interesting. We’re interested in intrinsic barriers, traits that prevent gene flow. For example, organisms can partition resources by using different host plants or by eating or living in different parts of the same plant.

In the European corn borer, there are so many individual traits that eliminate a small amount of gene flow, but none of them alone is sufficient to create a new species.

Do you spend a lot of time outdoors in the field?

When I think of questions that interest me, I imagine myself in the field, but when I answer the questions, I prefer to spend my time in the lab. There’s a significant amount of risk involved in field experiments. One flood, and there goes your experiment. Perhaps I’m too risk averse.

We do have field sites in Massachusetts where European corn borers are already present. We have some planned experiments in which we’ll move genes between our two strains of European corn borers. Then we’ll bring the corn borers into the field—kept in large cages—to find out how each gene affects the speciation process.

Most of my time is spent in data analysis. Nowadays, collecting data can take weeks, and then you spend months analyzing billions of base pairs of DNA.

How did you become interested in evolutionary biology?

When I was growing up, I thought I wanted to be a surgeon. The complexity of the human body as a puzzle appealed to me. I hadn’t really been exposed to evolution as a high school student in Texas for several reasons, some of which are more obvious than others.

As an undergraduate student at the University of Texas at Austin, I took a course with Eric Pianka, a world-renowned expert in evolutionary ecology, particularly the ecology and evolution of reptiles and lizards. His course opened my eyes to an area of research that connected with me. It gave me a conceptual framework to apply order to what I saw at the time as a hopelessly complicated natural world. The idea that one can model the fundamental processes that underlie this complexity was both foreign to me and also somewhat mysterious and thus exciting. It gave me an alternative path that was very different from the one that I had originally considered.

Through that class, I was able to find an undergraduate research opportunity with a graduate student named Greg Sword.

What was the research project?

We were studying a relative of the biblical plaguing locusts. These are essentially big grasshoppers. My initial day-to-day activity involved looking at grasshopper poop underneath a microscope. Since they are herbivores, if you look at grasshopper poop, you can see small little hairs—called trichomes—on the plants that they eat and these are species specific. Using these tell-tale hairs, we were able to determine that there were two kinds of grasshoppers that were eating two different kinds of plants.

One of the plants conferred toxicity to the grasshoppers that ate it, and those grasshoppers were colored very strongly black and yellow. That’s called aposematic coloration. It advertises to the grasshoppers’ predators that they are poisonous. It’s a warning. In many insects, black and yellow means “don’t touch me, stay away.”

But the other kind of grasshoppers were feeding on a plant that made them very, very palatable. And it turned out that they blended in with their background. That’s called cryptic coloration. It makes sense that you don’t want to advertise yourself if you’re actually a tasty morsel.

Then I did a genetic analysis that showed the two kinds of grasshoppers were in fact two different species. By comparing their genes, we determined that individuals feeding on the same plant species were more closely related to one other than they were to individuals that fed on the other plant species.

What do you like about being a biology professor?

As a graduate student, I was frustrated because it was impossible to be involved in all of the cool questions that one could imagine. As a professor, I get to experience the thrill of studying many more questions with students and postdocs. So I can actually have many, many projects ongoing at once. That’s one of the best parts of this job.

Is there a downside?

I think they’re one and the same. Being pulled in so many directions at once can be overwhelming. The difficulty is partitioning my brain enough to store all the details of the job. 

Do you consider yourself creative?

I would like to. Creativity is a critical component of being a successful scientist and doing successful research. You also have to be intimately familiar with the literature and the state of the art in your field. Under those conditions, you prepare yourself to recognize when something is unusual and therefore worth pursuing.

What advice do you give your students?

Concern yourself with the process of work. Worry less about outcomes. Be present. Engage in the process of doing science.

Jacqueline Mitchell can be reached at jacqueline.mitchell@tufts.edu.