"Plankton, which are key consumers of algae and a food source for many fish, may be making a monumental tradeoff to tolerate increased road salt. The circadian rhythm guides these animals through a daily migration, to deep waters during the day to hide from predators and shallow waters at night to feed. Disrupting that rhythm could affect the entire lake ecosystem," study co-author Rick Relyea explained in a News Medical article.
According to senior author Jennifer Hurley, adaptation to environmental toxins such as road salts might be affecting the plankton species at the epigenic levels. To examine this, the researchers have first noted that the plankton is regulated by a core set of clock-control genes that oversees the day and night cycle. According to the research team, these clock control genes take charge of various functions: such as promoting and suppressing gene transcription; and developing daily oscillations that impact cell function, division and growth. The scientists have also checked other physiological parameters such as the animals' temperature and immune responses.
Likewise, the research team has studied that expression of the mRNA of PERIOD (PER) genes in Daphnia exposed to low salt levels and dark conditions. The results have shown that despite the low salt levels and constant darkness, the plankton's PER mRNA levels oscillated with a 24-hour rhythm, which indicates a functional circadian clock. (Related: Biological clock disruption in humans may lead to cancer, study finds.)
Toxin exposure impacts circadian rhythm in plankton
The scientists have also performed a similar test on the plankton using a high-salt environment. The researchers observed that the animals' PER mRNA rhythms have shown a drastic deterioration upon exposure to increasing salt concentrations.
"What we see is a graded, measured response in this organism; the higher the level of salt to which the Daphnia are adapted, the more it suppresses the expression of its circadian clock. This research shows that exposure to environmental toxins may be depressing the function of our circadian clock, the disruption of which is linked to increased rates of cancer, diabetes, obesity, heart disease, and depression," Hurley has told Science Daily online.
"The implications are substantial. You've exposed Daphnia to an environmental toxin, and its clock was suppressed, probably through epigenetic mechanisms. The clock and biology of Daphnia is very similar to the clock and the biology both in our brains and most organisms. Is it possible that we can see epigenetic changes in the human brain because of exposure to environmental toxins?," Hurley adds.
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