The C. elegans roundworm sees by eating, sucking in big gulps of bacteria to learn about its surrounding environment. As researchers watched, they noticed an odd pattern marked by "bursts" of eating.
UChicago scientists in a new study use a mathematical model to explain such eating bursts. The findings, published Aug. 10 in Proceedings of the National Academy of Sciences, help inform a broader understanding of animals' feeding behavior and the science of decision-making.
"It's an interesting model for understanding the processes that underlie how animals decide where and when to eat," said lead author Monika Scholz, a Howard Hughes Medical Institute international student research fellow with UChicago's Biophysical Sciences program and now at Princeton University. "For these worms, it's all about the balance between speed and accuracy."
Roundworms live in big colonies in soil, such as compost piles, searching for bacteria to eat. Because they lack eyes, roundworms taste as they travel, but every gulp comes with a cost: The bite could contain delicious bacteria, or toxins, or nothing, in which case they've spent energy with no outcome.
Eat more to learn more
The straightforward prediction would say the worms should eat a lot when food is available, and stop when there is no food. But recent laboratory advances made it possible to collect data on worm feeding over longer periods—an hour or more rather than just a minute or two—and researchers began to notice an odd burst feeding pattern that didn't always correlate to the amount of food available. In particular, this intensified when the amount of food was fluctuating quickly.
When the data are laid out with a model that mathematically analyzes decisions, Scholz said, the pattern makes more sense.
"What we see is it's an evidence accumulation task," Scholz said. "Whenever the worm needs more information, it keeps taking bites. But if I keep changing the conditions while you're still deciding, the information is worthless. So the worm keeps trying to accumulate more and more evidence to make its decision, and you see this erratic pattern."
Understanding these systems is helpful because all animals, including humans, similarly make a great deal of decisions about when and where to feed, Scholz said.
"Most organisms live on the boundary of just enough to survive, so there is high evolutionary pressure to be good at these decisions," she said. "Systems for regulating food intake have evolved under situations where food is scarce," she added, which can provide insight into how human systems may have evolved.
"Currently much of our understanding of decision-making is investigated at two levels: At a purely theoretical level that is typically very removed from actual data, and psychology/animal behavior studies in complex mammals, which are complicated due to a lot of other factors that influence decision-making," Scholz said. "So what you have is two very distant levels of understanding. What research like this can do—basic research in simple organisms—is bridge that gap."
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Monika Scholz et al. Stochastic feeding dynamics arise from the need for information and energy, Proceedings of the National Academy of Sciences (2017). DOI: 10.1073/pnas.1703958114