Jan. 11 (UPI) -- Marine worms use ultraviolet light to tell what time of year it is and adapt their behavior accordingly.
The phenomena, described in a new paper published Monday in the journal Nature Ecology and Evolution, could help scientists better understand seasonal cycles in marine ecosystems.
"Many processes in the oceans are intrinsically rhythmic ... but we still understand only very little about their driving forces and controls," study co-author Kristin Tessmar-Raible told UPI in an email.
"Marine rhythms are crucially important for the stability of marine ecosystems," said Tessmar-Raible, a marine biologist at the University of Vienna in Austria.
Most research into how organisms sense seasonal changes have focused on day length -- sometimes referenced as the "photoperiod" by biologists.
Initially, scientists set out to measure the light conditions experienced by Platynereis dumerilii worms in Italy's Bay of Naples. The small marine "ragworm" species is found in many coastal waters in temperate to tropical zones.
"Like fruit flies or mice, these worms serve as a biological model system to understand basic biological processes that are of broad biological relevance, potentially including human biology," Tessmar-Raible said.
When scientists analyzed their initial light data, they were surprised to find seasonal ultraviolet light levels follow a seasonal pattern distinct from changes in day length.
To figure out whether the marine worms were sensitive to this pattern, researchers built special lamps in the lab to recreate the shifting light conditions.
Experiments showed one of the worm's key light receptors, called c-opsin 1, was able to sense changes in UV light.
Worms with c-opsin 1 altered enzyme levels in response to ultraviolet light changes, while worms in which c-opsin 1 had been silenced showed no physiological response to UV light patterns.
The enzymes produced in response to c-opsin 1 activity are responsible for the synthesis of neurohormones such as dopamine and serotonin.
Tessmar-Raible suggests it makes sense for animals to rely on different types of signals to trigger seasonal behavior changes.
"If there is a thunderstorm it can get quite dark even in summer -- or in the oceans- heavy rain can lead to very turbid and dark waters," she told UPI. "So, biological systems are often relying on environmental information coming in from more than one cue, because it makes them much less vulnerable to changes."
"There is likely an additional reason for using UVA light, because likely the worms want to react differently even if day length is the same, e.g. in spring a certain day length will be followed by the summer, whereas in fall the exact same day length will be followed by winter," Tessmar-Raible said. "Just relying on day length would not be enough, because they can't discriminate what time of the year to prepare for."
The findings could have implications for the study of ultraviolet light's impacts on other animals.
"Mammals also possess a light receptor of the opsin class that can sense UVA/deep violet light," Tessmar-Raible said. "In fact this opsin in mouse has just been shown to sense light directly in the brain itself."
In future studies, Tessmar-Raible plans to continue to investigate the ways different light sources influence the physiology and behavior of animals, especially in the marine environment.