Image: UCSD

When it comes to conservation-developing plans, say, to protect an endangered species-scientists often look at a population's genetic biodiversity to gauge its health. Preference goes to those with deeper gene pools, which are deemed better able to withstand environmental change. But a new study shows that this approach might overlook many creatures worth preserving. In today's Science, researchers from the University of California at San Diego and the Louisiana State University describe their findings on Acanthinucella spirata, a marine snail found throughout California in many forms.

"Looking at the coast today, there's a dramatic decline in genetic diversity in this species going from south to north," Kaustuv Roy from UCSD says. "But the northern regions have a greater amount of morphological diversity. So which do you use to make conservation decisions-genetic diversity or morphological diversity? Here's a case where the two come into conflict." The team discovered the north-south difference when they analyzed the mitochondrial DNA sequences of 117 snails from 14 populations. They also compared the shapes and sizes of the snails' shells with those found in the fossil record dating back to the Late Pleistocene 125,000 to 11,000 years ago. (The image at right shows the difference between a northern shell [top] and a southern shell [bottom].)

To explain their findings, the scientists suggest that the northern snails probably died out in a series of ice ages during the Pleistocene and earlier. Only later, when the planet warmed again, did gastropods from the south repopulate the northern range, probably between 12,000 and 30,000 years ago, judging from shell traits. "When adaptive evolution happens, it happens quickly," Michael Hellberg of LSU explains. "As a result, the neutral genetic markers commonly used for assessing population uniqueness may not always spot populations with novel adaptive characteristics worth preserving."