Spineless, quirky snails have much to teach us, UW expert shows
Alan Kohn in his Kincaid Hall lab.
We’re sitting in the College Inn Pub, a popular, smoke-filled beer bunker a block from campus, when the conversation turns from sports to movies. I seize an opportunity. “Has anyone seen Orlando?”
Bob hasn’t but Dave has. He’s even read the book. “Why do you ask?”
“I was hoping to work a little shameless anthropomorphizing into a creature feature I’m writing. But I haven’t seen the movie or read the book.”
In the movie, based on Virginia Woolf’s novel, the title character, an immortal, wakes up as a woman after spending a couple of centuries as a man.
“What causes the change? Ennui? I need to know.” “It’s not clear in the book or the movie,” Dave says. He mentions something about Orlando’s onset of ladyhood having followed war and an unrequited love. Maybe the combination did the trick.
This much is certain: There is no intimation, not even in the most arcane literary journal, that Orlando owes his/her sex change to barnacle repellent or any other chemical. But that’s how these things happen in real life.
“I may not be able to work Orlando in after all,” I say. “What is your story about?” Dave asks.
“It’s partly about a case of gender-bending in the wild kingdom, about an Orlando-like change in reverse. There are female snails in Puget Sound that can grow penises.”
Bob laughs. Dave sits up in his chair and says,
“You’re kidding.” They’ve heard tall tales from my side of the room before. This is on the level, I insist, slamming a fist onto a wobbly table. It tilts. Beer spills.
“And that may not be the most remarkable thing about these animals,” I say. “Their tropical cousins paralyze fish with venom so powerful it can kill a man. Or a woman. Or a woman who used to be a man. And this venom has turned out to be an ally for neurobiologists wiretapping the secret conversations of cells.”
While a hermaphroditic snail is good bar talk, it is also a sobering canary-in-a-coal-mine act that points to a dangerous chemical in the waters of Washington and British Columbia, says Alan J. Kohn, a UW zoology professor.
Kohn is the UW’s foremost expert on marine invertebrates, spineless creatures that live in the sea. The Smithsonian Press calls Kohn the world’s leading authority on marine cone snails. In 1992, the Smithsonian published Kohn’s A Chronological Taxonomy of Conus, 1758-1840, which clarified the murky record for hundreds of species described by early naturalists. “And we’re finding new species all the time,” says Kohn.
The Northwest’s sex-changing snails are not unique among more than 500 species that belong to Conus (for its conical shell), the largest animal genus in the marine world. Kohn has looked at the phenomenon, known as “imposex,” in species on the other side of the globe too.
The culprit is a substance called tributyltin, or TBT, used in ship-bottom paint to kill barnacles and other marine organisms.
The snails, an inch or two long including the shell, don’t cling to boats. The complication arises from simply being there, in water with minute, spit-in-the-ocean concentrations of TBT. The chemical induces a testosterone rush in a female, and a spare part sprouts.
The U.S. Environmental Protection Agency banned TBT in 1987, not because of its effects on snails but because of the hazard it posed to marine organisms in general. Canadian authorities continue to hedge on a TBT ban for all ships, and a Canadian colleague of Kohn’s has reported female snails with male organs is pandemic in British Columbia. Kohn’s own students recently found that half the female snails at Alki Beach in West Seattle are hermaphroditic.
Oddly, the new equipment is about as innocuous as a teeny-weeny bolo tie—it doesn’t seem to interfere with a snail’s ability to mate or to lay eggs, Kohn says.
A conus miles snail eats an eunicid sea worm.
Though Kohn’s name (pronounced, naturally, “cone”) resembles the species he studies, the homophone had less to do with his career path than geography. “I grew up in the New Haven (Conn.) area,” he says, “and wanted to do work in the tropics,” where the greatest diversity of cone snail species thrive in coral reefs.
For the past 40 years, during which Kohn received a Ph.D. from Yale, he has pursued Conus from Hawaii to Indonesia to Australia to most any other tropical place you could name. His main tools are a snorkel and, to inspect the fossil record, a rock hammer. “Of course, we have to put names on all these animals,” he says. “But the main goal is to understand how the snails can use the resources without competing and knocking each other out of existence.”
On Kohn’s office wall I notice a Far Side cartoon by Gary Larson, famous for his shameless and very funny anthropomorphizing. Two bugs are in a burrow, and one of them nags something like, “You call this a niche?”
Later I ask Kohn about the snail’s niche in a coral reef. Kohn, ever the patient educator, says “niche” is passe in ecology. I’ve been set up by a cartoonist. I feel as if I should be sitting in a corner wearing one of those cone-shaped hats. Or perhaps the shell of the giant Conus leopardus, a 9-incher. “The shell looks like a tusk,” Kohn says.
Instead of niche, he says “role” is a more acceptable term, then explains that most of the snails act as “secondary consumers,” feeding on animals that eat plants or small organic particles. Most are on a strict diet of segmented worms, the marine equivalent of earthworms. Small groups—”primary carnivores,” Kohn says—eat other snails and shellfish, and a few eat fish. “That’s one of the snail’s claims to fame: It’s the only invertebrate that hunts a vertebrate.”
Most species won’t sample dishes outside their broad category of choice. And “the diet of a given species is pretty similar whether it lives in Indonesia, India or Inhambane (Mozambique).”
Cone snails owe much of their global success to the sea currents, which they ride as larval specks in plankton. And that ability explains how the progeny of the first Conus 55 million years ago—fossils of a slightly later vintage can be found in western Washington amidst the hills of Tukwila and along the banks of the Cowlitz River—have come to inhabit nearly every tropical and temperate corner of the planet.
Female cone snails, with or without the extra equipment, aren’t the worst mothers. True, they don’t guard their offspring (a clutch can contain more than a million), but snail eggs come with a tough coating and are laid under rocks and in other protected places, Kohn says. Even the large eggs are less than a millimeter in diameter. It takes between two and three weeks for the eggs to hatch, depending on the amount of yolk. They are born with tiny shells.
“When they come out, they have to feed immediately through two U-shaped structures,” Kohn says. Their food consists of small particles in the plankton. They propel themselves to the plankton by wiggling cilia, hairlike protrusions that cover bands extending from the body. Once in the plankton, the ciliated bands ensnare morsels. After a week or so, gravity takes over. The larger larvae that don’t become meals themselves settle to the bottom, smaller versions of their parents. Smaller larvae spend about a month in the plankton.
Small egg species must have bigger geographic ranges,” Kohn concludes, “because their larvae must stay afloat, feed and grow for a longer time. They are dispersed wherever the currents take the plankton.” And if they’re lucky, the habitat will provide the meal of choice.
A Conus retifer snail, with its multicolored siphon at right.
One of Kohn’s latest studies is a comparison of egg size, larval development and dispersal, and geographic range for more than 60 Indo-Pacific cone snail species. Oxford University Press has just published the results as Life History and Biogeography: Patterns in Conus. Frank E. Perron, a New Hampshire environmental consultant and former UW post-doctorate researcher, is co-author.
Kohn has been with the UW for the past 32 years, teaching the zoology department’s venerable invertebrate zoology course, which celebrates its centennial this academic year. Kohn supposes that “probably some students think I’ve given the course since its inception.”
Those students 50 or 75 years ago should have been so lucky. Kohn’s conversation is sprinkled with references to former and current students. He has cut them in on his research and has been generous with the credit. He grabs three reprints of scientific articles to illustrate his work’s range. They reveal something else: On each, the lead author is a student; Kohn gets second billing.
One of the papers is titled, “The Functional Morphology of the Conus Proboscis.” It’s the first detailed description of the workings of the cone snail’s hollow, tongue-like organ.
The paper mentions a fish-hunting species with a three-barbed tooth at the tip of its proboscis that it shoots into prey like a harpoon. “It uses the tooth once,” Kohn says. “It has a whole quiver of teeth.” A cone snail’s proboscis may be only inches long, but in some species it can stretch four times its contracted length—and half again the length of its shell.
Through the proboscis and tooth the snail injects, hypodermic-fashion, a neurotoxic venom that paralyzes the prey. Like a snake’s throat over an egg, a sheath surrounding the proboscis engulfs the fish—and the tooth that stung it—and the snail reels the already digesting food through the tube into its gut. Kohn says meal time is quite a sight: The prey can be nearly as long as the predator.
But how does a gastropod that may be the slowest of famously slow creatures get the drop on blennies and gobies and other tidepool prey much less sluggish than itself? It relies on stealth, tracking with a chemical, fish-finding sense akin to smell.
Humans get into trouble when they grab or step on some types of cone snails. At least 30 people have perished this way, most of them in Guam and other nearby islands.
To a few isolated peoples, cone snails become escargot, Kohn says. “And to get married, Punjabi women must wear a bangle made of the shell. Other than those, Conus utility to man is indirect.”
Indirect, maybe, but profound, at least to one group: neurobiologists who conduct basic research on the nervous system. Much of their work now depends on Conus venom. Different toxins, or conotoxins, in the venom can block specific ion channels, the paths through which nerve impulses travel on their way to the muscles and the brain.
The active ingredients in venom are short protein fragments called peptides. In the early 1980s, University of Utah biochemist Baldomero Olivera led a team that started separating active conotoxin peptides from each other, rendering forms useful in nerve and muscle studies.
“He took up the Conus venom study where I left off a long time ago,” Kohn says. (Kohn and Olivera have just embarked on a study that ties Conus ecology to properties of its venom.)
Between 1978 and 1982, only six scientific articles on conotoxins were published, and Olivera was an author on half of them, including one about isolating the potent and probably the most experimentally useful peptide so far, one from fish-hunting Conus magus. A search of “conotoxin” on UW Libraries’ Medline database reveals 43 references between 1983 and 1987. From 1988 through 1993, the number jumps to about 600.
UW researchers haven’t been watching from the sideline.
“Any one species of snail has in its venom a veritable cocktail of neurotoxic peptides, each of which seems to be a very specific blocker of a particular one of the many ion channels in nerve or muscle cell membranes,” says Bertil Hille, a UW professor of physiology and biophysics.
Hille says conotoxins are used in at least four UW labs, including his. Hille studies the boggling complexities of how hormones and neurotransmitters tell vital cells and neurons to turn on and off.
“We’re interested in elaborating the specific molecule-to-molecule steps in intracellular signaling pathways,” Hille says. He says that by finding out which molecules are interacting with each other, molecular biologists can “make sense of why this chain of events occurs, and we can predict in what other cells the same events are likely to be happening.”
He likens the process to puzzling out how what might euphemistically be called “sensitive information” is spread among politicians and those who would seek to influence them. “Did Mr. Clinton speak to Mr. Foster who spoke to Mr. Y who runs the bank? Or was it Mrs. Clinton who spoke to Sen. W by a different pathway? This is the detail we want in chemical conversations.”
A conotoxin that can block one of the channels, a specific calcium pathway—one that can shut up Mr. Y or Sen. W, say—”is a neat way of showing if the message transmission is still the same, if that channel is the pathway activated by several neurotransmitters,” Hille says.
Kohn suggests that the reason venom is so valuable in basic research may also render it medically useless: It blocks those crucial pathways so completely and relentlessly that a non-toxic form might be impossible to engineer.
At least that’s what Kohn used to think. Somewhere in Hille’s neurotoxic cocktail may be the equivalent of a low-alcohol beverage, a light beer that works great and is less killing.
The other day a pair of researchers from the University of Queensland, Australia, paid Kohn a visit. They’re working on medicines, Kohn says, and are particularly interested in less toxic peptides that could offset side effects of a drug prescribed for Alzheimer’s disease.
Another claim to fame for the conical snail?