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Updated 11:00 AM July 16, 2007
 

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  Research
Tahitian tree snails may still have a future, U-M study suggests

Despite the recent mass extermination of Tahiti's colorful tree snails, it may still be possible to preserve much of their original genetic diversity in the wild, research by U-M mollusk expert Diarmaid O’Foighil and collaborators suggests.

The work, which relied on 600 vials of freeze-dried samples collected in 1970 and left untouched in a freezer for more than 30 years, is reported in the July 3 issue of Current Biology.

Tahiti’s tree snails, famous since the late 1800s as classic examples of species that had rapidly diversified in an isolated environment, later became victims of a “spectacularly inept attempt at biological control,” O’Foighil says.

Up until the mid-1970s the Society Islands, which include the island of Tahiti, were “a biodiversity hot spot for tree snails,” containing about half the described species in the snail family Partulidae, he says. But that all began to change when the predatory rosy wolf snail was deliberately introduced to many South Pacific islands to control an agricultural pest. Unfortunately, the snail had a bigger appetite for native land snails than for the pests it was supposed to devour. Before long the native snails had been virtually wiped out.

Researchers and conservationists stepped in during the 1980s and began setting up captive populations in European and North American zoos—eventually including the Detroit Zoo. “Only a few years ago, it looked like the sole survivors would be the captive populations,” O’Foighil says. “But our results suggest it may be possible to maintain genetically representative remnant wild populations in Tahiti, although this will require proactive conservation measures.” In the study, researchers compared the genetic diversity of tree snails that remain in the wild and in captivity to that of the 1970 specimens, which were collected by Professor Emeritus John (Jack) Burch before the rosy wolf snail was introduced and began decimating native snails.

“Although severe winnowing of lineage diversity has occurred, we were pleasantly surprised to discover that the small surviving populations that persist on the island contain genetic contributions from all of the primary historical Tahitian lineages present in our museum collections,” O’Foighil says. “Our study therefore keeps open the possibility of preserving a representative—although impoverished—sub-sample of the island’s original tree snail genetic diversity, something that previously did not seem plausible.”

The findings also point to the conservation value of museum specimens and fundamental science, says O’Foighil, a professor of ecology and evolutionary biology and a curator in the Museum of Zoology. “Jack Burch went to Tahiti in 1970 as a museum curator engaged in basic, collection-oriented research. He didn’t know the snails were going to go extinct—in fact, they were so plentiful that collecting them was like picking berries.”

Burch collected several thousand specimens. Most were preserved in alcohol for anatomical studies, but he also shipped about 600 live snails back to U-M to be freeze-dried. At the time, researchers used proteins to study relationships among species, and freeze-drying preserves proteins. The plan was for Burch and a collaborator in Hawaii to use the freeze-dried material for a detailed study of evolutionary relationships. But the collaborator died before the research could be done, and Burch became absorbed in other projects, leaving the vials of freeze-dried snails in three wooden trays in a freezer at the Museum of Zoology.

In a chance conversation with Burch, O’Foighil learned of the specimens and immediately grasped their value. He and colleagues went to work extracting, amplifying and analyzing DNA from the samples and using the information to construct evolutionary trees they hoped would help conservationists decide which wild populations to focus their efforts on.

“Jack Burch’s Tahitian tree snail collections, which had no special conservation value when they were collected, now are priceless,” O’Foighil says.

U-M coauthors on the Current Biology paper are Burch, Taehwan Lee, assistant research scientist, and Younghun Jung,research associate. Other colleagues include Trevor Coote of the International Partulid Conservation Programme in Papeete, Tahiti, and Paul Pearce-Kelly of the Zoological Society of London. The researchers received funding from the National Science Foundation and La Direction de l’Environnement de Polynésie Française.

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