Behavioural evidence for a sleep-like quiescent state in a pulmonate mollusc, Lymnaea stagnalis (Linnaeus)

Abstract

to sleep; resting wakefulness, paralysis, hibernation, torpor, akinesis, diapause, aestivation, anaesthesia and coma all share this characteristic. However, only in sleep and resting wakefulness is the suppression of motor output rapidly and spontaneously reversible. The second criterion, reversible suppression of sensory responsiveness, characterizes a quiescent state as sleep-like, and Accepted 15 November 2010 SUMMARY The objective of this study was to determine whether the great pond snail, Lymnaea stagnalis, expresses a sleep-like behavioural state. We found that snails spontaneously enter a relatively brief (22±1min) quiescent state characterized by postural relaxation of the foot, mantle and tentacles, and cessation of radula rasping. Quiescence was reversed ('aroused') by appetitive (sucrose solution) and aversive (tactile) stimuli. Responsiveness to both stimuli was significantly lower in quiescent snails than in active snails. However, tactile stimuli evoked a more sustained defensive response in quiescent snails. Quiescence bouts were consolidated into 'clusters' over an infradian timescale and were only weakly affected by time of day. Clusters contained 7±0.5 bouts, lasted 13±1h and were separated by long (37±4h) intervals of almost continuous activity. Analysis of Kaplan-Meier survival curves revealed that the quiescent bout duration was described by an exponential probability distribution (time constant 15±1min). Active bout duration was described by a bi-exponential probability distribution (time constants 62±4 and 592±48min). We found no evidence for a 'sleep rebound' mechanism and quiescence expression appeared to be regulated through stochastic processes causing state transitions to resemble a Markovian random walk. We conclude that Lymnaea is a potentially valuable model system for studies of cellular function in sleep.

Honeybees consolidate navigation memory during sleep

“…Sleep, as defined by a state of rest, reduced sensory sensitivity, relaxed muscle tonus and altered neural activity, is well known across the animal kingdom from mollusks (Stephenson and Lewis, 2011) to humans. The role of sleep is likely to be manifold, but one particular property appears to exist across animal species -the supportive effect on memory consolidation.…”

Liberating Lévy walk research from the shackles of optimal foraging

“…This suggests that some snails, who also have this type of movement, could be performing Lévy walks and Stephenson and Lewis [136] report tentative evidence for this in the great pond snail, Lymnaea stagnalis; durations of bouts of 'active-run' movements were, to a good approximation, bi-exponential, but that a slightly poorer fit to these data could also be achieved with a power-law. The fittings were, however, obtained using a nonlinear regression technique rather than more conventional, and more widely accepted, maximum likelihood methods.…”

Behavioural Contagion Explains Group Cohesion in a Social Crustacean

“…Our experimental and theoretical results strongly suggest that the aggregation process during the retention phase may promote a collective entry into a behavioural quiescence or sleep-like state (see [20], [55–57]). Entrance into a sleep-like state could explain why woodlice can be observed for several dozen minutes in apparently unfavourable places (exposed at light and without cover) when isolated individuals quickly run away in similar conditions.…”