August 8, 2012 | 4
Last May, a University of Alabama graduate student was the first person to collect an oblong rock snail in over 70 years. The species, Leptoxis compacta, hadn’t been observed since 1933 and was declared extinct in 2000. Nathan Whelan, the biology PhD candidate who made the discovery, is glad that his research has a positive aspect to it. “Conservation and biodiversity stories that you hear nowadays are usually negative—talking about the biodiversity crisis, all these species going extinct,” he says. “To find one that was thought to be extinct was very exciting.”
Unfortunately, the story is not all rainbows and unicorns for the striped snail. L. compacta used to live in a 50-mile stretch of the Cahaba River and Buck Creek in Alabama, but currently it only seems to inhabit about a quarter mile of the river. Being isolated in one tiny location makes the species very susceptible to a single disruptive event that could wipe it out for real this time.
Whelan was interested in L. compacta because it was the only snail in its taxonomical family and geographical area to have gone extinct (or so people thought). “Since there was never a really good explanation as to why that species went extinct and others did not, I thought there may be a small chance it was still out there,” he says. His instinct paid off in May 2011 when, during a research trip by kayak to a remote part of the river, he and a few colleagues found the long-lost mollusk. The remoteness probably contributed to the incorrect diagnosis of extinction, but three previous mollusk collection surveys, conducted by government agencies and individual researchers in the past 20 years, failed to find L. compacta at the site of rediscovery. “This may indicate that the species was even rarer in the recent past,” Whelan says.
To verify that the snails they found were indeed L. compacta, Whelan’s group compared the shells and radulae of the newly found mollusks to those preserved in museums. The radula is the structure a mollusk uses to feed. It’s made of chitin, like an insect exoskeleton, and consists of a ribbon of tiny teeth attached to a membrane. With the blessing of Smithsonian curators, Whelan’s group was able to remove the bodies from the shells of two L. compacta snails collected in 1881 and preserved in the National Museum of Natural History. They used enzymes to dissolve the soft tissue, leaving only the hard radulae, and compared scanning electron micrograph images of radulae from the two historical specimens to those of several of the newly collected snails. The radulae and shells matched historical individuals almost exactly, so researchers are confident in their identification.
Freshwater snails are important members of their ecosystems. They keep rivers clean by grazing on diatoms and algae, and they serve as food sources for fish and crayfish. “They’re incredibly integral to basic ecological processes in many of the rivers in the Southeastern United States,” Whelan says. Plus, they’re cool. Underneath their fairly tame shells, members of L. compacta have bright yellow bodies with black banding. “They’re more colorful and cooler than people may realize,” Whelan says.
Prior to L. compacta‘s rediscovery, little was known about its life cycle and reproductive strategy. Both are important in deciding what kinds of conservation efforts will be most effective. Whelan’s group brought about thirty members of the species to the lab for observation. The snails laid eggs in captivity, and researchers were able to watch juveniles develop over the course of several months. Whelan says that being able to identify juveniles is important for monitoring the species.
The researchers’ observations make them optimistic about conservation possibilities. Since the snails can reproduce in captivity, it may be possible for conservationists to breed them in a lab and then re-seed parts of their old territories with new populations. This reestablishment would help mitigate the risk of extinction from one big event.