It's a snail-eat-snail world out there
St. Louis Post-Dispatch
By Jeffrey Bonner
October 5, 2008
In the 10th report of a monthly series this year, Saint Louis Zoo President Jeffrey Bonner explores a part of the globe where the Zoo is working to conserve threatened species, protect natural habitat and partner with other organizations to strengthen the web of life in which we all live. See story this story in St. Louis Post-Dispatch.
Zoos work to protect Partula snails from extinction.
Not every animal at the Saint Louis Zoo is exactly what you'd call charismatic. Take the case of the Partula Snail.
The family Partulidae is a group of tree snails that evolved in the tropical South Pacific Islands. Partula snails are diverse, with more than 100 different species. Their range is vast, covering about 5,000 miles from Palau to the Society Islands, but it is on the Society Islands that Partula snails took off. The Society Islands have a variety of different microenvironments that range from moist, tropical valleys to dry, windswept ridgetops. Where one finds pronounced environmental variation, animals adapt to different environments and gradually evolve into totally different species. In fact, this small group of islands has about 50 different species of Partula snails.
From a human point of view, Partulas are relatively harmless: They eat microscopic plants that grow on the undersides of leaves, but they don't eat the leaves themselves. They're attractive little guys that vary in color from pale to dark brown. Many of the species have a lovely spiral pattern on their shells. Even the biggest Partula species gets to be only about an inch long.
But humble though they may be, Partula snails are very well known to science. They occupied a major part of the battleground between the proponents of Lamarck's theory of evolution, based on acquired traits, and the proponents of Darwin's theory, which was based on natural selection. Both sides used Partula snails to support their theories.
The principal "biographer" of the Partula genus was Henry Edward Crampton, a 20th century paleontologist and evolutionary biologist who studied them for more than 50 years on Tahiti and neighboring islands. Three scientists, Brian Clarke, Jim Murray and Mike Johnson, have continued to build on Crampton's monumental work on the island of Moorea (better known by its stage name, Bali Ha'i, from the musical "South Pacific), about 15 miles from Tahiti.
When they began their work in the 1960s, they thought they would be studying the snails' continued evolution; they never dreamed they would be documenting the snails' demise.
The problem began in 1967, when a large African tree snail, Achatina, was deliberately introduced on Tahiti as a food source. When I say large, I mean large: they grow up to nine inches in length and are said to be delicious. Achatina snails quickly outwore their welcome, stripping the island's crops and gardens bare. Before long, they hopped a boat to Moorea, where their population continued to explode. Like some sci-fi thriller, Clarke, Murray and Johnson write of removing two wheelbarrow loads of the giant African terror from inside one house. (Imagine how many were outside.)
At the peak of the crisis, the French government of Tahiti turned to a snail named Euglandina rosea for help. E. rosea, a Florida native, is carnivorous; it eats other snails. (I don't know how it eats other snails, so don't ask. Honestly, though. Can you imagine the thrill of the hunt, as E. rosea "races" toward its intended victim? The horrible thudding sound as it crashes into its prey, crawling at full speed? The lightning quickness of the kill?)
Clarke, Murray and Johnson thought releasing E. rosea was, well, dumb. In fact, most ecologists - familiar with the disasters wrought by introduced species in other parts of the world - protested the government's decision. They were right.
E. rosea never developed much of a taste for the giant African snail, but it did develop a hearty appetite for Partulas. Between 1977, when it was introduced and 1984, E. rosea ate every single member of one of the seven species of Partulas on the island. By 1988, it nearly had polished off the remaining six species.
But, luckily, they weren't gone entirely. Once the three scientists realized that one species of Partula was extinct, they put out a call to save the remaining six species by breeding them in zoos. In 1990, the zoo world created a breeding plan to save the Partula snails, coordinated by the late Ron Goellner, then the Saint Louis Zoo's general curator.
The Partulas live on today, tended by a cadre of loyal volunteers, not in their beautiful island paradise but in small, plastic sandwich boxes stacked in the Monsanto Insectarium at the Saint Louis Zoo and the back rooms of other zoos around the world. Will the Partulas ever roam free on their island again? Probably not. In all likelihood, their future is here where they are safe but not saved. Perhaps it is not enough, but at least it is something.
Republished with the permission of the St. Louis Post-Dispatch
Copyright 2008 St. Louis Post-Dispatch
Courtesy of STLtoday.com