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

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'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.