A new study by University of Michigan biologists suggests that some predatory marine cone snails evolved a highly diverse set of venoms that enables them to capture and paralyze a broad range of prey species.
When cone snails sink their harpoon-like teeth into their prey, they inject paralyzing venoms made from a potent mix of more than 100 different neurotoxins known as conotoxins.
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.
U-M researchers showed that the mix of neurotoxins in cone-snail venom varies from place to place and is more diverse at locations where the snails have a broad range of prey species. In addition, they concluded that the observed patterns of local conotoxin variation are likely due to natural selection.
That's a significant finding 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.
In addition, the U-M researchers were able to directly target the genes responsible for the observed conotoxin patterns. A paper summarizing the work was published online in the journal Proceedings of the Royal Society B March 18, 2015.
"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," said first author Dan Chang, formerly a doctoral student in the U-M Department of Ecology and Evolutionary Biology and now a postdoctoral researcher at the University of California, Santa Cruz.
"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," Chang said.
The other U-M authors are Thomas Duda and Amy Olenzek, who was an undergraduate student in Duda's lab at the time. The study was funded by a National Science Foundation grant to Duda, who is an associate professor in the Department of Ecology and Evolutionary Biology and an associate curator at the U-M Museum of Zoology.