Seminars on Science
Claudia Englbrecht

Claudia Englbrecht, a postdoctoral fellow at the American Museum of Natural History from 2000-2001, was born in Munich, Germany. As a girl, she wanted to become a medical doctor, like her father, but he counseled her against it. So when Claudia enrolled at the University of Munich, she decided to study biology, with a major in zoology and minors in biochemistry, human genetics, and ecology. In her research for her Master's thesis, Claudia used DNA sequencing to explore the evolution of small freshwater crustaceans.

Dr. Englbrecht stands outside the American Museum of Natural History.
Dr. Englbrecht stands outside the American Museum of Natural History. ©AMNH

The evolution of species is normally represented as a tree of forked lines, with new species branching out from older ones. Once separated, these branches do not connect again, because different species do not interbreed. But under a theory called reticulate evolution, interbreeding can occur between closely related species, which means the evolutionary tree can sometimes look like a web (reticulate comes from the Latin word for net).

To find evidence for reticulate evolution, one would have to look at a species' DNA, because animals exchange genes when they interbreed. Claudia focused on related species of the genus Daphnia , which were thought to have evolved by reticulation. She sequenced DNA samples from several individuals in each species to look for signs of past or present interbreeding. "Sequencing then was not like it is today," she remembers. "It was such a hassle, and it took so long." Though Claudia was working less than a decade ago, DNA sequencing technology was far less automated than it is today, and much more laborious.

Since her supervisor was not trained in molecular biology, Claudia had to figure out what she was doing as she went along. Ultimately she got what she needed: enough lab experience to continue her research after graduation.

After studying Daphnia for another year, Claudia entered a Ph.D. program. For her doctoral research, she continued to explore the process of evolution, particularly speciation, or how one species might evolve into two separate ones. The most common cause of speciation is that animals from a single species become separated geographically. Because they are no longer able to interbreed, they evolve along different paths. This is called allopatric evolution.

Claudia was interested in a less popular theory, called sympatric evolution. According to the sympatric theory, animals can go down different evolutionary paths without being geographically separated. For example, by developing different feeding habits, two distinct species of the same fish can evolve in a single lake. But it is hard to prove that this has happened after the fact. "The problem with speciation," Claudia explains, "is that you look at species when they are already present—the end product. It's hard to see the process." Fortunately, an animal's genetic history is recorded in its DNA.

Claudia decided to use DNA sequencing to search for signs of sympatric evolution among Arctic char. "It's a good fish—it tastes better than trout," she says with a grin. But more importantly—to an evolutionary biologist at least—it is highly polymorphic, meaning the species has many forms, or "morphs." In some places, up to four different morphs of Arctic char live together in a single lake.

"The question is," Claudia wondered, "are these morphs different species? And if so, did they evolve in one lake?" If they had, it would be a clear example of sympatric evolution.

Claudia takes a little R & R in the German Alps. ©Alex Greenwood
Claudia takes a little R & R in the German Alps. ©Alex Greenwood

Claudia's fieldwork involved traveling to scenic lakes at the base of the Alps to collect the fish she needed to study. "I really enjoyed being outdoors," she recalls fondly. "Sometimes, we would stay at the lake for days. I would walk up in the mountains, and stay in a little cabin." Being outdoors made her glad she had chosen to study biology. "It was a good combination of lab work and leaving the lab to go out into nature," she says.

Unfortunately, Claudia could find only one lake in Germany that had two morphs of char in it. And even there, she found just eight samples of one morph—not enough to do a species analysis. Worse yet, the lakes had been stocked with fish for decades, so there was no way to know where the char actually came from. This made them less useful for research, since the essence of sympatric evolution is that the species must evolve in the same place.

Fortunately, other fish in the alpine lakes had never been stocked, including the lowly bullhead, a small fish useless to the commercial fishing industry. Claudia discovered that two groups of bullheads were living in one very deep lake in Bavaria. One group lived near the surface, the other 190 meters down, at the bottom of the lake. If these different behavior patterns had caused the groups to evolve apart, it would be an example of sympatric evolution.

The beautiful lake was in a national park in Bavaria. "It was very special just to be there," Claudia recalls. "It was out of season, and we were the only ones there. It was sort of like 'our' lake." To gather samples from both groups, Claudia and her advisor hired a crew with a small, submersible boat that allowed two people to venture to the bottom of the lake. "That was fun," she says, though she admits, "I was scared. It was a tiny little boat. "

When Claudia returned to Munich and examined the fishes' DNA, however, she found no genetic difference at all between the two populations. Furthermore, the fish at the bottom carried a parasite that could only be picked up near the surface, which meant they must have been in the shallow part of the lake at some point in their lives. This was clearly not a case of sympatric evolution—there were no signs the two groups had begun to evolve apart at all.

But Claudia was not finished with her studies of bullheads. Since they live throughout Europe, Claudia decided to examine the DNA of bullheads from as many different locations as she could, to see if the history recorded in their genes showed the path they took as they first spread across the continent. Recreating their evolutionary tree could also help reveal the history of the river systems of Europe.

Claudia sequenced DNA from bullheads all over Europe and found that they fell into six groups, each of which had branched off the bullhead family tree at a different time. Using this genetic evidence, she concluded that bullheads entered Central Europe from the Black Sea, and then spread west and north. The fishes' DNA also revealed the effects of the huge glaciers that covered northern Europe during the Pleistocene Epoch. Bullheads from areas that had once been covered by ice showed far less genetic diversity than bullheads from other climates. Claudia concluded that the bullheads now living in these places had all descended from a small group of "pioneers" that resettled there after the glaciers receded.

While deep into her research, Claudia learned that other researchers were studying the same fish, including teams from Belgium, France, and England. "I won the race," she recalls with a rueful smile. "I couldn't back down—I already had 400 animals." But she was weary of the frustrations and competitive nature of academia, and when she completed her Ph.D., she turned her sights toward private industry.

Dr. Englbrecht in her submersible in Lake König, Germany. This device facilitated her research dives. ©Claudia Englbrecht
Dr. Englbrecht in her submersible in Lake König, Germany. This device facilitated her research dives. ©Claudia Englbrecht

Though her friends were landing good jobs with biotech companies in Munich, Claudia's thoughts were on America. Claudia had stayed in Munich to finish her Ph.D., but she now wanted to live in the U.S. She set herself a time limit of three months—the length of a tourist visa—to find a job; if she didn't, she would go home. Fortunately, while visiting New York she was offered a year-long postdoctoral position at the American Museum of Natural History, so she moved to Manhattan.

Her supervisor while at AMNH, Museum Curator Rob DeSalle, not only does research in molecular evolution and co-directs the Museum's molecular labs, but also serves as a scientific consultant for the Museum's children's magazines, teachers' guides, books, online professional development courses like this one, and the children's website, OLogy . Claudia's responsibilities included sharing Rob's duties as an advisor for these projects.

The shift from research to education brought new challenges as well as new satisfactions. Though Claudia was familiar with the elaborate review process required for scientific publications, she was surprised to find the process of creating publications for children just as rigorous. Every word has to be revised, tested, and rewritten for young readers by an editorial team with experience in children's publications. She can express herself more freely writing for the online genetics course, because she can write essays at an adult level on subjects that especially interest her. "The purpose of the course is to give people a solid, informed basis to talk about issues like cloning, selecting genes, and assessing risk," she says. Although the course focuses on ethical questions, Claudia also draws on her research experience to write about topics such as the tools and techniques used in molecular labs.

It has been a wonderful experience sharing her knowledge with others. "In research, you're always struggling and worrying whether you've read all the latest publications," she says. She marvels at her new role as a teacher, saying "For the first time, you have the feeling that you really know something." Though she considers herself a shy person, Claudia enjoys discussing genetics with nonscientists.

After working at the AMNH, Claudia moved back to Germany in June of 2001 to work in a bioinformatics research institute. She admits that the Museum had a strong impact on her career—the Museum's focus on genomics sparked her interest in working to analyze genome sequences. She points out that "the bulk of sequences generated everyday is only raw data and needs interpretation in order to understand it." Currently she works on the computational interpretation of bacterial DNA, using computer programs to find genes in the raw DNA sequence and to infer their function.

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