Sea Snails Disable Prey With a Toxic Dose of Insulin

Slow-moving and lacking typical fighting parts, cone snails are not your average fearsome predator; but that doesn't mean they aren't lethal. These fish-eating sea snails make up for their inadequacies by using a unique kind of weaponry that delivers a toxic dose of insulin to effectively disable their prey, a new study finds. 

"It is very unlikely that it is serving a different purpose," lead author Helena Safavi-Hemami, a research assistant professor at the University of Utah, said in a statement.

"This is a unique type of insulin. It is shorter than any insulin that has been described in any animal," added senior author Baldomero M. Olivera. "We found it in the venom in large amounts."

Cone snails all produce a distinct repertoire of fast-acting venom compounds used to target the nervous systems of prey, such as zebrafish, rendering them useless. Conus geographus, a species that has killed dozens of people in accidental encounters, is one such cone snail capable of immobilizing unsuspecting fish. According to popular belief, this paralyzing predator protrudes a stretchy mouth-like part and, like a gun, aims it at its target prey and shoots a venom mixture into the water. The fish becomes disoriented and stops moving altogether, letting the snail move in and engulf its helpless meal.

In order to better understand this slow-motion trap, Utah researchers analyzed the gene sequences of all the proteins expressed in the venom gland of Conus geographus. They were surprised to find two sequences that looked similar to that of the hormone insulin, which normally functions to regulate energy metabolism. What's more, the insulin genes were expressed more so than most genes for the snail's venom toxins.

Researchers decided to test out a synthetic form of the snail insulin by injecting it into zebrafish. Consequently, their blood glucose levels plummeted and their ability to swim was compromised when brought in contact with affected waters. It should be noted that not all cone snail species boast this unique immobilizing insulin. It is present in Conus geographus and Conus tulipa, which both practice the same fish-trapping method; however, fish-eating cone snails that are ambush hunters - attacking with a harpooon-like organ - and those that prey on mollusks and worms do not have insulin in their venom.

Snails may be slow-moving, but their fast-acting insulin weaponry more than makes up for it, successfully disabling entire schools of swimming fish with one hypoglycemic shock.

The findings were published in the journal Proceedings of the National Academy of Sciences.

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