You might not think that speedy, nimble fish would be the ideal prey for sluggish sea snails, but certain predatory species have evolved some truly remarkable mechanisms to ensnare their dinner. Humble-looking cone snails, for example, take down their prey with a cocktail of toxins that rapidly attack the nervous system.
But it turns out that’s not the only form of chemical warfare that these cunning marine predators adopt. According to a new study, two species first send their victims into a stupor by drugging them with a weaponized form of insulin, making them easier to capture with their mouthparts. The researchers believe that throwing this hormone into their toxic arsenal could allow the snails to subdue schools of fish by sending them into hypoglycemic shock.
Cone snails, or members of the Conus genus, are predatory marine molluscs found in warm seas and oceans across the world. All cone snails are venomous, but each species produces its own unique blend of toxins that has evolved to target particular prey; larger species go for small fish, whereas the smaller species tend to hunt worms. Because the venom sends prey into a dazed state, it has been nicknamed “nirvana cabal.”
But it’s not just small bottom-dwellers that fall victim to these unassuming predators; they’re also renowned for stinging scuba divers who are enticed by their beautiful, brightly colored shells. One particularly deadly species, the geographic cone snail (Conus geographus), has even killed a number of people in accidental encounters.
Cone snails deliver their venomous toxins through a harpoon-like modified tooth that acts like a disposable, hypodermic needle. But two species that target fish, C. geographus and C. tulipa, also practice a netting strategy that involves engulfing prey with huge, gaping mouthparts. So how do these slow moving gastropods snare nimble fish? Scientists believed that they likely squirted a toxic cloud of chemicals into the water that immobilized and confused the fish, giving the predators time to slowly advance. But they weren’t sure what was responsible, so a team of scientists from the University of Utah endeavored to find out.
Interestingly, they discovered that their venom contained large amounts of a unique form of the hormone insulin, which is used throughout the animal kingdom to regulate metabolism by promoting the removal of excess glucose from the blood. Further digging revealed that this insulin is distinct to the one used by the predators to regulate their own blood sugar. Not only is it extremely small, but it also displays similarities with the insulin produced by their fish prey. Furthermore, they couldn’t find this particular fish hormone in the venom of smaller cone snail species that prey on worms or molluscs, rather than fish.
When the researchers directly injected this insulin variant into zebrafish, their blood sugar plummeted and they went into hypoglycemic shock. But when they added it to their water, they immediately went into a stupor and began swimming much more slowly. The researchers therefore speculate that these two species sedate their prey by giving them an overdose of insulin. And if this variant turns out to be particularly potent, the researchers may eventually be able to use these findings to develop better treatments for diabetes.