Energy conservation characterizes sleep in sharks

Abstract

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 characterize 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.

Persistence of Nocturnality in Decapitated and Bisected Flatworms

“…As a result, sleep is thought to play a role in the maturation of the central nervous system ( Roffwarg et al, 1966 ), and has at least the potential to do so in decapitated flatworms ( Omond et al, 2017 ). Second, sleep saves energy by (1) lowering metabolic rate, (2) not doing something more energetically demanding, and (3) partitioning metabolic processes to either sleep or wakefulness ( Lesku et al, 2006 ; Schmidt, 2014 ; Ferretti et al, 2019 ; Kelly et al, 2022 ; Lesku and Schmidt, 2022 ). The energy saved by sleeping can then be reallocated to other purposes, such as investment into the immune system ( Preston et al, 2009 ).…”

The effect of fishing‐capture stress on the oxygen uptake rate and swimming activity of the holocephalan Callorhinchus milii

“…The data recorded while the animal was swimming/resting were used to calculate Active/Inactive Ṁ O 2 (“ Ṁ O 2 ‐type”). Because Ṁ O 2 takes some time to decrease and stabilize after switching from swimming to resting (Piiper et al, 1977), only periods during which an animal swam or rested continuously for at least 5 min were included in calculations (Kelly et al, 2022). For the eight measurement cycles and for the swimming and resting series of data, DOs were plotted over time (Supporting Information: Materials) and a regression slope was calculated.…”

Just keep swimming? Observations of resting behavior in gray reef sharks Carcharhinus amblyrhynchos (Bleeker, 1856)

“…For bony fishes, most studies have characterized behavioral criteria associated with sleep, evidencing circadian rest–activity cycles in several species (Zhdanova, 2011). For sharks and rays, information on sleep is even more sparce, with most studies relating periods of sustained restfulness and reduced responsiveness to sleep‐like behavior (Kelly et al, 2022; Siegel, 2009). Several studies have presented evidence for a sleep‐like state in buccal pumping species (Kelly et al, 2020; Kelly et al, 2021) but, given that sleep is typically characterized by prolonged immobility, evidence for sleep in ram ventilating species is much more difficult to define.…”