Jellyfish and sea anemones surprisingly sleep like humans to protect nerve cells

Amazing stuff!

"Turns out jellyfish and sea anemones – among the ancient creatures with a nervous system instead of a brain – have a very similar sleeping routine to our own. A new study published in Nature Communications reveals that these animals not only sleep but do so for the same portion of their day as humans, spending about one-third of the day sleeping. The findings also suggest that sleep evolved long before the brain to help maintain cells under stress. ..."

"... the most basic and ancient role of sleep is to protect nerve cells from cellular stress and the accumulation of DNA damage. ..."

From the 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.

Light and homeostasis were the primary drivers of sleep in C. andromeda, which slept at night and napped at midday in both the laboratory and the natural habitat. In contrast, both the circadian clock and homeostatic processes regulated sleep in N. vectensis, which increased sleep at dawn.

Similar to humans, C. andromeda, wild-type (WT) and Clock mutant (NvClkΔ/Δ) N. vectensis slept about one-third of the day, irrespective of the daily timing and architecture of sleep, and melatonin promoted sleep in accordance with the species-specific chronotype.

Notably, sleep deprivation, ultraviolet radiation, and mutagens increased neuronal DNA damage and sleep pressure, while spontaneous and induced sleep facilitated genome stability in both the diurnal and crepuscular cnidarians. These results suggest that DNA damage and cellular stress in simple nerve nets may have driven the evolution of sleep."

Jellyfish and sea anemones surprisingly sleep like humans

Why Do We Sleep at All? The Surprising Answer from the Sea (original news release) "Researchers at Bar-Ilan University decode an ancient sleep mechanism and reveal that sleep protects nerve cell."

DNA damage modulates sleep drive in basal cnidarians with divergent chronotypes (open access)

Fig. 1: Generalizing the characterization of sleep in C. andromeda across sizes and habitats.

Fig. 4: Sleep reduces DNA damage in neurons of cnidarians.