"Wonder Drug" Snails Face Threats, Experts Warn
John Pickrell in England
for National Geographic News
|October 16, 2003|
A new report warns that a group of tropical sea snails, famous for yielding new wonder drugs to treat chronic pain, cancer, and many other afflictions, could rapidly become extinct if measures are not taken to protect them.
More than 2,600 scientific studies over the last 20 years testify to the important contribution toxins extracted from cone snails have made to medicine and cellular biology. To date only 100 out of a potential 50,000 toxins have been extracted and analyzed. Despite this, few measures have been put in place to regulate exploitation or trade in these species, 69 percent of which live within regions where coral reefs are threatened by human activity.
The 500 known "tropical cone snails may contain the largest and most clinically important pharmacopoeia of any genus in nature," said medical scientist and study author Eric Chivian of Harvard University in Cambridge, Massachusetts. "But wild populations are being decimated by habitat destruction and overexploitation. To lose these species would be a self-destructive act of unparalleled folly."
The study is detailed in a letter to appear tomorrow in the research journal Science.
Beautiful yet deadly, cone snails mostly inhabit the shallow tropical waters of coral reefs or mangrove swamps. They harpoon other invertebrate prey with a concealed hollow tooth, through which they inject conotoxin venom. The venom is a mixture of different toxic protein molecules, of which each species might possess 100 varieties. Constantly revising that recipe makes it more difficult for prey to evolve resistance.
Cone snail shells come in a dazzling array of colors and patterns, said the letter's co-author, ecologist Callum Roberts at the University of York in England. "But as swimmers who made the mistake of tucking an attractive shell into their costume have found out, they produce a powerful venom." That poison is strong enough to paralyze or kill a person.
The snails' toxin molecules work by disrupting communication between cells, and this activity has made them very useful for understanding how cells work. However, the area in which conotoxin research shows the most promise is in clinical medicine. Treatments are under development for neurological auto-immune diseases, cancer, and chronic pain. One new synthetic drug developed from a conotoxin may be a thousand times more potent than morphine without any of the addictive properties. Conotoxins also have the potential to treat epilepsy and clinical depression.
Degradation and Exploitation
So far, as few as 100 venom molecules have been studied, with 95 percent of research carried out on just three of the 500 known species of cone snails, said Roberts. However, concurrent with the increase in interest in these species, they are facing threats in the wild as never before.
Although there has been little documented evidence of cone snail extinctions, "the reason we're very worried is that we know all the prerequisites for species to go extinct are in place," said Roberts. Many species live in narrow ranges, a fact that combined with wide-scale habitat destruction and exploitation for trade is a "lethal cocktail," he said.
The study reports 88 percent of Southeast Asia coral reefs are threatened by human activities. The region is home to 56 percent of cone snail species. Worryingly, nearly 70 percent of species face habitat loss in more than half of their current geographic ranges.
Habitat loss is exacerbated by direct exploitation. The attractive shells are collected in their millions from Mexico, Indonesia, Fiji, and elsewhere, and sold in seaside resort towns worldwide, said Roberts. It's not just the tourist industry though, he added. One unnamed U.S. research institute recently imported the venom glands from 10,000 snails collected in China.
"The recent increase in bioprospecting provides levels of harvesting which may well accelerate the current rates of decline," commented Mary Seddon, World Conservation Union (IUCN) mollusk specialist and biodiversity scientist at the National Museums and Galleries of Wales in Cardiff. Bioprospecting is the process of searching for new medicines, and otherwise useful compounds in nature.
Despite these threats, very few mollusk species enjoy international protection. "There are only five species of [cone snails] listed on the IUCN red list of globally threatened species," said Seddon. "This is not a true reflection of the potential threats of extinction for the rare and narrowly localized species."
The Convention on International Trade in Endangered Species (CITES), which serves to legally protect threatened animals, should be extended to cover cone snails, argues the Science letter. Earlier this month, additional protection was given under this convention to the queen conch mollusk, a popular food item famous for its enormous pink shell.
If the cone snail genus was added to a part of the CITES agreement known as Appendix II, their trade would be allowed to continue, said Roberts, but countries would be obliged to both monitor trade and limit exploitation.
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