It could be challenging for predators to catch their meal if they are not fast enough and more so if they do not have the typical fighting parts found in most predatory animals.
Two species of slow-moving cone snails, however, manage to catch fish for food with their unique ability that allows them to make up for their sluggishness.
For the new study published in the journal PNAS, researchers discovered that the fish-eating Conus geographus and Conus tulipa have the unique ability to use insulin to drug their prey before eating it.
The snails use a special form of fish insulin that can induce hypoglycemic shock in their prospective meal. Unlike other predators that pursue their prey, these snails wait until a fish swims by before flooding the surrounding waters with insulin that suppresses glucose in the vital organs such as the brain of the fish, causing it to be lethargic and become an easy catch for the sushi-loving snails.
Study researcher Baldomero Olivera from the University of Utah said that the snail uses a unique type of insulin, shorter than any insulin that scientists have described in any animal and different from the one used by fish to manage their own sugar levels. The researchers likewise found the insulin in enormous amounts in the venom gland.
When Olivera and colleagues injected a synthetic form of this insulin into a zebrafish, it caused the fish's blood sugar levels to drop. They also observed that when they placed the insulin in the water where the fish swam, it disrupted the swimming behavior of the fish as indicated by the percentage of the time the fish spent swimming and the frequency of its movements.
The researchers posited that adding the insulin to its concoction of venom toxins allowed the cone snails to incapacitate a school of fish by causing their blood glucose levels to plummet.
"We already knew that these animals make hundreds of neurotoxins in their venom and compounds that cause tissue degradation and affect cardiovascular function," said study co-author Helena Safavi from the University of Utah. "Now we can add yet another mechanism to this list: the disruption of the prey's energy metabolism."
The researchers are now looking at the cone snails' genes that code for the insulin to determine whether the predatory mollusks developed their insulin from scratch or if this evolved from the animals' own insulin.
