Discovery of REM Sleep Rebound in Spiders
Researchers at the University of Bonn have discovered that Portia fimbriata spiders can make up for a lack of REM-like sleep by significantly increasing the frequency of characteristic limb movements following a night of sleep deprivation. This finding provides evidence that invertebrates display signs of REM rebound, a phenomenon thought to play a crucial biological role. The study revealed that after being kept awake overnight, these spiders exhibited nearly an 80% increase in movements typically associated with REM-like sleep.
During the experiments, the spiders were monitored using infrared cameras. While Portia fimbriata were active during the day, they adopted restful postures at night and showed reduced responsiveness to external stimuli. Their periods of stillness were periodically interrupted by movements of their legs, mouthparts, and eyes—behaviors resembling REM sleep in vertebrates. To induce sleep disruption, researchers introduced 25 live fruit flies into the spiders’ enclosures, preventing undisturbed rest.
The Significance of REM-like Sleep
The following night, the spiders demonstrated a nearly 80% increase in REM-like movements without extending the duration of these episodes, a phenomenon known as REM rebound. According to Nadia Geiger, one of the study’s authors, this is the first confirmed observation of REM rebound in invertebrates. She emphasized that
“REM-like sleep serves an essential biological purpose and is not a random feature of nighttime rest.”
The research team suggests that REM-like sleep may assist these spiders in processing information gathered during the day, consolidating memories, and refining their hunting strategies.
Similar behaviors were previously reported in 2022 by Daniela K. Ressler’s team in jumping spiders of the species Evarcha arcuata. These discoveries raise intriguing questions about whether spiders experience dreams, though definitive confirmation of sleep requires further investigation into neural activity during REM-like phases.
Identifying sleep phases in spiders, cephalopods, and vertebrates points to an ancient evolutionary origin for active sleep. However, more research is needed to fully understand the development and functions of active sleep across species.
This study highlights the importance of active sleep beyond vertebrates, potentially reshaping our understanding of sleep evolution. The evidence of REM rebound in spiders opens new avenues for exploring the neurophysiology of sleep across diverse animal groups. Future investigations may clarify the specific roles REM-like sleep plays in invertebrates and the evolutionary advantages it confers. These findings may also inspire broader research into sleep and memory, advancing our knowledge of sleep functions in living organisms.