Snail venom mixes and matches 100 neurotoxins

A Hebrew cone snail, Conus ebraeus, searching for food on a reef. (Credit: Jeanette Johnson)

When cone snails sink their harpoon-like teeth into their prey, they inject a potent mix of more than 100 different neurotoxin—known as conotoxins—that can be changed up depending on what’s for dinner.

The genes that provide the recipes for conotoxin cocktails are among the fastest-evolving genes in the animal kingdom, enabling these snails to constantly refine their venoms to more precisely target the neuromuscular systems of their prey.

New research study shows that cone snail venom varies from place to place—and is more diverse at locations where the snails have a broad range of prey.

Natural selection

The patterns of local conotoxin variation are likely due to natural selection. That’s a significant finding, researchers say, because it is often difficult for biologists to determine whether place-to-place variations in an organism’s observable traits—the wide range of beak sizes and shapes in the Galapagos Islands finches studied by Charles Darwin, for example—are the result of evolution by natural selection or some other factor, such as the reproductive isolation of a population of animals or plants.

For the new study, published in Proceedings of the Royal Society B, researchers were able to directly target the genes responsible for the observed conotoxin patterns.

“The differences in venom composition that we observed correspond to differences in prey, and a higher diversity of venom is used to capture more prey species,” says first author Dan Chang, formerly a doctoral student in the ecology and evolutionary biology department at the University of Michigan and now a postdoctoral researcher at the University of California, Santa Cruz.

Snail poop

“Our results suggest that prey diversity affects the evolution of predation genes and imply that these predators develop a more diverse venom repertoire in order to effectively subdue a broader range of prey species.”

The study involved a common species of tropical, worm-eating cone snail, Conus ebraeus, collected at locations in Hawaii, Guam, and American Samoa.

The snails are about an inch long and are commonly known as Hebrew cone snails. Their shells are white with black rectangular markings that form a distinctive checkerboard pattern.

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The researchers characterized the patterns of genetic variation in five toxin genes in C. ebraeus snails from the three locations. They also collected fecal samples from the snails to determine the types of worms they ate.

“We demonstrated that venom genes used for predation are highly affected by local variation in prey diversity and geographic heterogeneity in prey compositions,” Chang says.

“Not all conotoxin genes are affected in the same way though, which implies that these genes may have distinct functional roles and evolutionary pathways.”

The National Science Foundation funded the study.

Source: University of Michigan