It’s a question that has fueled more than one science fiction film: what sort of evolutionary changes occur within a species when—by virtue of choice, tides, or dumb luck—its members exist, generation after generation, in a cave environment?

Natalie Hanson (MS biology ’08) is replacing some of the fiction with fact. Since fall 2007, Hanson has been actively researching the metabolic rates of cave amphipods in comparison to their aboveground counterparts. “The lack of light means that most of the food in a cave is stuff that gets washed in,” she explains. “Because of the sparse food supply, you don’t want a super-fast metabolism that requires you to eat all the time.”

While research exists that examines the metabolic rates of cave organisms, Hanson’s methodology is unique. To date, the vast majority of these studies have used respiratory chambers to measure organisms’ oxygen consumption and thus determine their metabolic rates. But these chambers are quite large in comparison to amphipods—shrimp-like creatures that are about a centimeter long—and the considerable size disparity can lead to inaccurate measurements. For her experiments, Hanson is introducing stable isotopes into the amphipods’ food, where they act as a chemical tracer. “If you introduce an isotope into an organism’s diet, you can

watch it accumulate and calculate the organism’s metabolic rate based on this accumulation,” she says.

Hanson’s research consists of three phases, with each one representing a different length of evolutionary separation. Currently, she is comparing cave and surface amphipods of the same species; the second phase will compare cave and surface amphipods of the same genus but different species, and the third will compare cave and surface amphipods of different species and genera. The hypothesis? “That there will be a connection between the metabolic rate and length of evolutional time spent in caves,” says Hanson. “The longer the species has been in caves, the slower its metabolism will be.”

In addition to winning a fall 2007 Mellon research grant, Hanson has received financial support from the Cosmos Club of Washington, D.C., and the Cave Conservancy of the Virginias, a nonprofit dedicated to protecting and managing caves and karst resources in Virginia and West Virginia. “Part of conservation is gaining knowledge,” says Hanson. “By supporting research, the organization both adds to the knowledge base [related to caves and cave life] and gets the message out about the importance of cave conservation.”