If the white snails were similarly transported by accident, their distribution pattern should be random, with nearby islands being much more likely than more distant ones to have received them. "The fact that they're not present on nearby islands suggests deliberate introduction to the more distant archipelagos," Foighil said.
To investigate that possibility, the researchers conducted genetic analyses of snails from Tahiti and the Austral and Southern Cook Islands. The task was complicated by the dearth of wild snails on Tahiti, the result of a disastrous biological control experiment in which the predatory rosy wolf snail was brought to the island in 1975 to squelch an agricultural pest but feasted instead on native tree snails. Fortuitously, U-M professor emeritus John B. (Jack) Burch had collected Partula specimens in Tahiti in 1970, and those freeze-dried specimens still reside in the Museum of Zoology, where Foighil and assistant research scientist Taehwan Lee recently have been extracting, amplifying and analyzing their DNA and using the information to construct evolutionary trees. The researchers also had access to captive populations maintained in London Zoo.
The genetic analyses confirmed the Tahitian origins of the Austral and Southern Cook snails and suggested multiple prehistoric introductions from Tahiti. To understand what motivated early islanders to deliberately transport live snails, the researchers turned their attention from genetics to aesthetics.
"We know that Polynesians used these shells ornamentally. We think the fact that the white shells were aesthetically valuable within this regional trading network explains their unusual distribution," Foighil said. On Tahiti, where the shells were relatively common, they would not have been highly priz
|Contact: Nancy Ross-Flanigan|
University of Michigan