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Exposure to environmental toxins may be depressing the function of human circadian clock, the disruption of which is linked to increased rates of cancer, diabetes, obesity, heart disease, and depression. Plankton 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. Adaptation to salt is likely affecting Daphnia at the epigenetic level, a heritable change in gene levels rather than genetic code. The research has wide applicability in multiple fields beyond human health and is a demonstration of cutting-edge, interdisciplinary research.
To explore whether salt affects the circadian rhythm of Daphnia, researchers first established that the plankton is governed by a core set of clock-control genes that anticipates the day and night cycle. Clock control genes promote and suppress gene transcription, creating daily oscillations in the levels of enzymes and hormones to affect cell function, division, and growth, as well as physiological parameters such as body temperature and immune responses.
The Daphnia genome includes the PERIOD gene, a set of genes nearly identical to the well-established core clock of the fruit fly. Researchers tracked the expression of the mRNA of PER in Daphnia exposed to naturally low salt levels and constant dark conditions. Despite these constant environmental conditions, Daphnia PER mRNA levels oscillated with a 24-hour rhythm, a clear indication of a functional circadian clock.
This shows that PER “clock genes” are active in Daphnia. To test whether adaptation to high-salt environments affects this functional circadian clock, Researchers performed experiment with the five populations of Daphnia. The result showed that PER mRNA rhythms deteriorated with the adaptation to increasing salt concentrations.
The higher the level of salt to which the Daphnia are adapted, the more it suppresses the expression of its circadian clock. The population adapted to naturally low salt levels exhibits a beautiful, healthy oscillation in PER mRNA expression, but the population adapted to high salt levels have completely lost their ability to oscillate this mRNA expression.
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