The Jellyfish Cassiopea Exhibits a Sleep-like State

Area of Science:

• Zoology
• Neuroscience
• Evolutionary Biology

Background:

• Sleep is a fundamental biological process observed across many animal groups.
• Cnidaria, an early-branching metazoan lineage, possess a non-centralized nerve net but share fundamental properties with vertebrate nervous systems.
• Previous observations noted quiescence in some cnidarians, suggesting potential for sleep-like states.

Purpose of the Study:

• To investigate the presence of sleep in Cnidaria, specifically the upside-down jellyfish (Cassiopea spp.).
• To determine if Cassiopea exhibits behavioral patterns indicative of sleep, including quiescence, reversibility, and homeostatic regulation.

Main Methods:

• Long-term behavioral tracking of Cassiopea pulsing activity over consecutive days and nights.
• Monitoring quiescence periods, response to stimulation during quiescence, and activity levels after sleep deprivation.

Main Results:

• Cassiopea spp. displayed quantifiable nightly quiescence that was rapidly reversible.
• The jellyfish showed delayed responses to stimuli when in a quiescent state.
• Deprivation of nighttime quiescence led to decreased activity and responsiveness the following day, indicating homeostatic regulation.

Conclusions:

• The results strongly indicate that Cassiopea possesses a sleep-like state.
• This supports the hypothesis that sleep is an ancient trait that evolved early in metazoan evolution, predating the development of a centralized nervous system.