Mountain surprise for threatened snails

Abstract

At first sight it looks like an ecological disaster: an isolated island group of animals under assault from an alien and ruthless predator. This seemed to be the plight and fate of tree snails in Tahiti. In 1974, a foreign predatory snail was introduced which rapidly eliminated their endemic prey. Thirty years on, three of the island's eight endemic Partula species are officially extinct and a fourth exists only in captivity. But in a Correspondence reported on pages R502–R503 of this issue, Diarmaid Ó Foighil at the University of Michigan, Ann Arbor, and colleagues at the International Partulid Conservation Project in Tahiti and the Zoological Society of London, shed a glimmer of conservation light on this otherwise bleak scene. The researchers were able to get their results because one of the team, John Burch, collected extensive samples of all the nominal Tahitian Partula species, apart from one found exclusively in the mountains, four years before the predatory snail was introduced. The specimens were sent live to the University of Michigan where they were then dissected and samples of foot muscle from each individual freeze-dried and stored. From material taken from a sample of the 683 snail muscles preserved in this collection, the authors were able to assign a genotype for a mitochondrial marker amongst both the museum specimens and individuals from current captive and wild populations. The researchers found five primary clades amongst the snails for this marker and were surprised to find that living snails, mostly from the mountains, could still be assigned to four of these clades despite the massive loss of lowland animals to the introduced predator. The researchers also describe the finding of two nominal species, still persisting at low altitudes in 19 out of 69 valleys investigated, that formed the fifth distinctive clade. The researchers conclude that the historical diversity of these snails (in terms of this marker at least) remains, though is in a perilous state. And they point out that four of the five main historical clades are due to the presence of genetically diverse mountain populations. “Conservation of the island's remnant tree snail diversity is likely to require proactive maintenance of these threatened montane populations,” they say.