An undergraduate researcher from the Cáceres Lab recently investigated the role of melatonin on the disease dynamics between freshwater crustacean Daphia dentifera—commonly known as the water flea—and fungal parasite Metschnikowia bicuspidata. The results were published in Ecosphere.
This study looked at how melatonin—a hormone that changes throughout the day—affects the immune response of freshwater zooplankton called Daphnia dentifera. Ashley Cassens, the lead researcher tested how adding extra melatonin affected the likelihood of these animals getting infected by a fungus. They found that adding melatonin made it more likely for the Daphnia to get infected during the day, but not at night.
“Dr. Caceres had mentioned melatonin as a potential area to study as there hasn’t been a lot of research on melatonin in this organism specifically,” said Cassens. “We read a couple of papers by Dr. Anke Schwarzenberger who studied the effects of melatonin on the stress-response in Daphnia, and the circadian rhythm in Daphnia. I was fascinated by the fact that melatonin, something we produce or even take to help us sleep, could have a link to Daphnia and their susceptibility to infection as well.”
The research continued by looking at different stages of the infection process, including how the fungus enters the Daphnia's gut and body. It was found that melatonin slowed down how quickly the fungus passed through the gut, but didn’t affect whether it could enter the body or trigger an immune response. Ashley also noticed that Daphnia that molted (shed their outer covering) during melatonin exposure were more likely to get infected, likely because molting made it easier for the fungus to get in. In one experiment, Cassens didn’t see much effect of melatonin or molting on infection rates, possibly due to high death rates in the study.
“This study sheds light on the effect melatonin has on disease dynamics, especially in crustaceans,” said Cassens. “We found that the addition of exogenous melatonin during the day leads to increased susceptibility to infection and increased gut passage time, but less spores in the gut and nearly no significant findings about further mechanisms. Clearly more research needs to be done about the mechanisms of infection and melatonin’s role in immune response of Daphnia, as well as how it influenced Metschnikowia.”