Raphael Aguillon

Abstract Sleep is a conserved behavior across all animals with a nervous system, ranging from cnidarians to humans. Considering the survival risks, why sleep evolved in basal lineages and what essential benefits it provides to the simple nerve net of nocturnal and diurnal invertebrates remain elusive. We used behavioral criteria to empirically define sleep in the upside-down jellyfish Cassiopea andromeda and the starlet sea anemone Nematostella vectensis.

eLife assessment This fundamental study for the first time defines genetically the role of the Clock gene in basal metazoa, using the cnidarian Nematostella vectensis. With convincing evidence, the study provides insight into the early evolution of circadian clocks.

The concept of circadian rhythms is quite intuitive: life on Earth needs to be able to anticipate predictable changes in the environment – and take advantage of them. Thus, in most species, a wide range of bodily functions and behaviors are optimized to the time-of-day. Moreover, the disruption of circadian rhythms diminishes survival in the wild, and increases the risk of many diseases in humans (Lane et al., 2023).