MO2, behaviour data and supplementary material for the first physiological evidence of sleep in sharks

Sharks represent the earliest group of jawed vertebrates and as such, they
may provide original insight for understanding the evolution of sleep in
more derived animals. Unfortunately, beyond a single behavioural
investigation, very little is known about sleep in these ancient
predators. As such, recordings of physiological indicators of sleep in
sharks have never been reported. Reduced energy expenditure arising from
sustained restfulness and lowered metabolic rate during sleep have given
rise to the hypothesis that sleep plays an important role for energy
conservation. To determine whether this idea applies also to sharks, we
compared metabolic rates of draughtsboard sharks (Cephaloscyllium
isabellum) during periods ostensibly thought to be sleep, along with
restful and actively swimming sharks across a 24-h period. We also
investigated behaviours that often characterise sleep in other animals,
including eye closure and postural recumbency, to establish relationships
between physiology and behaviour. Overall, lower metabolic rate and a flat
body posture reflect sleep in draughtsboard sharks, whereas eye closure is
a poorer indication of sleep. Our results support the idea for the
conservation of energy as a function of sleep in these basal vertebrates.