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Student Reveals Evolutionary
Processes of Cave Organisms

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—they exist, generation after generation, in a cave environment?

Natalie Hanson, MS biology ’08, replaced some of these fictions with fact. As a master’s student, Hanson actively researched the metabolic rates of cave amphipods in comparison to their above-ground 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.”

 

A Unique Methodology

The vast majority of studies examining the metabolic rates of cave organisms have done so by using respiratory chambers to measure organisms’ oxygen. But these chambers are quite large in comparison to amphipods—shrimp-like creatures that are about a centimeter long each—and the considerable size disparity can lead to inaccurate measurements.

For her experiments, Hanson introduced stable isotopes into the amphipods’ food, where they acted 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.

 

The Project Continues

Hanson’s research project compared cave and surface amphipods of the same species. Her results showed a definite connection between the organisms’ metabolic rates and length of evolutional time spent in caves. This answer led to another question: Just how different are the metabolic rates of cave and surface amphipods?

Since Hanson’s graduation in 2008, Dina Lloyd, MS chemistry ’09 has been working on finding an answer. Lloyd is increasing the duration of Hanson’s experiments in order to determine the quantitative difference between surface and cave amphipods’ metabolic rates.

The project has received funding from a variety of sources, including a CAS 2007 Mellon Research Grant, 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.”