Tiny worms make complex decisions, too

The findings, published inCurrent Biologyon March 7, 2022, have important implications for the way researchers assess motivation and cognitive abilities in animals. What's more, the study demonstrates that complex decision-making capabilities could be encoded in small biological and artificial networks.

"Our study shows you can use a simple system such as the worm to study something complex, like goal-directed decision-making. We also demonstrated that behavior can tell us a lot about how the brain works," says senior author Sreekanth Chalasani, associate professor in Salk's Molecular Neurobiology Laboratory. "Even simple systems like worms have different strategies, and they can choose between those strategies, deciding which one works well for them in a given situation. That provides a framework for understanding how these decisions are made in more complex systems, such as humans."

Whether eating prey or defending its food source, the predatory wormPristionchus pacificusrelies on biting. The team's challenge was to determine the worm's intentions when it bites.

The researchers found thatP. pacificuschooses between two foraging strategies for biting its prey and competitor, another worm calledCaenorhabditis elegans: 1) predatory strategy, in which its goal for biting is to kill prey, or 2) territorial strategy, in which biting is instead used to forceC. elegansaway from a food source.P. pacificuschooses the predatory strategy against larvalC. elegans, which is easy to kill. In contrast,P. pacificusselects the territorial strategy against adultC. elegans, which is difficult to kill and outcompetesP. pacificusfor food.

To the team, it appeared thatP. pacificusweighed the costs and benefits of multiple potential outcomes of an action -- behavior that's familiar in vertebrates but unexpected in a worm.

"Scientists have always assumed that worms were simple -- whenP. pacificusbites we thought that was always for a singular predatory purpose," says first author Kathleen Quach, a postdoctoral fellow in Chalasani's lab. "Actually,P. pacificusis versatile and can use the same action, bitingC. elegans, to achieve different long-term goals. I was surprised to find thatP. pacificuscould leverage what seemed like failed predation into successful and goal-directed territoriality."

In the future, the scientists would like to determine which ofP. pacificus' cost-benefit calculations are hard-wired or flexible. They hope more research like this will help further uncover the molecular underpinnings of decision-making.

The research was supported by the National Institutes of Health (5R01MH113905), the W.M. Keck Foundation, the National Science Foundation, Salk Women & Science and a Paul F. Glenn Foundation Postdoctoral Fellowship.