Yale study suggests worms can "see" color even without eyes
Yale researchers have found evidence that a worm species can detect the color blue – even though it doesn’t have eyes, or any kind of visual system that it should, by all accounts, require. In tests, the team found that the color of harmful bacteria influenced whether or not the worms would avoid them.
The worm species C. elegans forages for bacteria in the soil where it lives, but one of its least favorites is Pseudomonas aeruginosa, a toxic microbe that also happens to be bright blue. That said, its color wasn’t thought to play a direct role in the worms’ avoidance behavior – after all, C. elegans is not just blind, but it has no eyes, photoreceptors, or even the requisite genes that let animals perceive color.
But in the new study, Yale researchers discovered that the blue coloring does influence the worms’ behavior. Somehow, the creatures seem to be cobbling together some other method of color perception.
The strange finding came out through a series of experiments on a variety of C. elegans strains and P. aeruiginosa cultures. The team tried switching out the bacteria’s blue toxin for a harmless blue dye, while they gave another batch a colorless version of the toxin. The worms didn’t squirm away from either of these the way they did from the regular bugs.
In other tests, the team shone light of different colors onto colorless E. coli, a bacteria that C. elegans often eats. Some strains of the worms avoided their harmless food under certain lighting, while others needed both a certain color and a chemical signal to decide to steer clear of a given bacteria. Either way, the team says the color of the light was at least partly influencing the worms’ behavior.
Going further, the team was able to identify two genes in particular that are associated with the ability to perceive color. In other animals, these genes are related to cellular stress response pathways, and are activated by UV light. While the researchers aren’t sure exactly how it works, they speculate that the worms are somehow using these pathways to perceive color, as one tool in their arsenal of sensing the environment around them.
“What the worm is doing is something very smart,” says Michael Nitabach, co-author of the study. “They are trying to generate a more accurate picture of external reality by employing multiple senses at same time.”
More studies will no doubt be needed to better understand this feat of nature, but it’s another intriguing example of how invertebrates can be craftier than we give them credit for.
The research was published in the journal Science.