Gina Johnson
Lizards are a diverse group of reptiles with over 7,000 species, and their sleeping habits vary widely. While most lizards have eyelids and close their eyes when they sleep, geckos are an exception. Geckos are lizards in the infraorder Gekkota, and all gecko species except for leopard geckos and their close relatives lack eyelids. These lizards sleep with their eyes open but are still unconscious. Geckos without eyelids have a clear scale covering each eye, which must be kept clean to maintain their vision. Interestingly, recent studies have found that lizards, including geckos, experience similar sleep stages to humans, including REM sleep. However, the length of their sleep cycles differs, with a fast sleep cycle for a lizard lasting about 80 seconds compared to 60 to 90 minutes for humans.
| Characteristics | Values |
|---|---|
| Do lizards have eyelids? | Most lizards have eyelids and close their eyes when they sleep. The only group of lizards that don't have eyelids are geckos, which are lizards in the infraorder Gekkota. |
| Exceptions | Geckos of the subfamily Eublepharidae have working eyelids. Examples include leopard geckos, banded geckos, and fat-tailed geckos. |
| How do lizards without eyelids sleep? | Lizards without eyelids have a clear scale covering each eye. They sleep with their eyes open, but their brains still shut down, and they are unconscious. |
| Do lizards have REM sleep? | Yes, lizards have REM sleep, just like humans. However, it is unclear if they have complex dreams like humans do. |
| Sleep stages | Electrodes placed on the brains of bearded dragons recorded evidence of lizards going through the stages of human slumber: slow-wave sleep, sharp waves, ripples, and rapid eye movement (REM). |
| Sleep duration | The amount of time a lizard sleeps depends on its species and environmental factors. Lizards sleep for as short as four hours a day to over 18 hours. |
| Sleep cycle duration | A fast sleep cycle for a lizard is 80 seconds. For a house cat, it's 30 minutes, and for humans, it's 60 to 90 minutes. |
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What You'll Learn
Geckos are the only lizards without eyelids
Geckos without eyelids have a few adaptations to keep their eyes clean and moist. Firstly, they have a clear, fused scale that covers each eye, which must be kept clean so their vision does not become impaired. This scale gets shed like the rest of the lizard's external scales. Additionally, geckos lick their own corneas to keep their eyes clean and moist. They also have special glands that help keep their eyes moist.
Geckos without eyelids constrict their pupils as much as possible when they sleep. Geckos typically hide themselves under tree bark, in a cavity, or another sheltered space when sleeping. While most geckos are nocturnal, some are diurnal, meaning they are active during the day. Nocturnal species typically have elliptical pupils like cats, while diurnal species tend to have round pupils.
Interestingly, geckos are not the only lizards that experience sleep in a similar way to humans. A recent study found that the bearded dragon, a native Australian lizard, goes through almost the same sleep stages as humans. Electrodes placed on the surface of five bearded dragons' brains recorded evidence of the lizards going through the stages of human slumber: slow-wave sleep, sharp waves, ripples, and rapid eye movement (REM). This discovery was surprising because, until recently, scientists had only studied the brain activity of sleeping mammals and birds, not non-avian reptiles.
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Geckos without eyelids constrict their pupils as much as possible
Geckos, like all animals, need sleep. However, unlike humans, most geckos do not have eyelids, so they cannot simply close their eyes when they want to sleep. Geckos in the subfamily Eublepharidae are the exception, with around 40 species possessing eyelids.
Geckos that do not have eyelids have evolved to have a clear, fused monocle covering each eye, which they must keep clean to avoid impaired vision. They also have large eyes and pupils, which can contract and expand to control the amount of light entering the eye.
When geckos without eyelids feel the need to sleep, they constrict their pupils as much as possible. This allows their eyes to absorb as little light as possible, replicating the action of closing one's eyes. Owners of pet geckos can tell when their gecko is sleeping by looking at the size of its pupils; if the pupils are thin, barely-visible slits, the gecko is probably sleeping.
Geckos without eyelids also lick their own corneas to keep their eyes clean and moist. This is necessary because, without eyelids, they are unable to blink, which would usually serve to moisten and protect their eyes.
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Geckos with eyelids include leopard, banded, and fat-tailed geckos
Banded geckos, or Coleonyx sp., are native to North America and are one of the oldest genera within the eyelid gecko subfamily Eublepharinae. They are ground-dwellers and lack the specialised toe pads found in other geckos.
Fat-tailed geckos, or Hemitheconyx caudicinctus, are native to Africa and are one of the most commonly kept Eublepharid geckos. They live in arid areas and hide in burrows, requiring a habitat that is slightly more humid. Like leopard geckos, they have thick tails that store fat, which can be used as a source of nourishment when food is scarce.
While most geckos lack eyelids, those that do have them are able to shut their eyes when sleeping. Geckos that do not have eyelids instead constrict their pupils as much as possible while sleeping. Interestingly, recent studies have shown that lizards go through similar sleep stages as humans, including slow-wave sleep, sharp waves, ripples, and rapid eye movement (REM) sleep. However, the length of their sleep cycles differs, with a fast sleep cycle for a lizard lasting only 80 seconds compared to 60 to 90 minutes for humans.
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Geckos without eyelids have a clear scale covering each eye
Geckos are a diverse family of over 1,500 species found worldwide in an array of habitats, including deserts and rainforests. They have highly specialised lidless eyes, which have several evolutionary advantages. Geckos without eyelids have a clear scale, known as a brille, ocular scale, eye cap, or spectacle, covering each eye. This clear membrane functions like a built-in lens shield, protecting the eye from dust and dirt.
Geckos without eyelids have evolved alternative methods to keep their eyes clean, moist, and healthy. For example, they lick their corneas to keep them clean and moist. Some geckos also have a nictitating membrane, a second translucent lower lid that provides extra protection and moisture when burrowing. In addition, gecko eyes produce a thick oily tear film.
Geckos without eyelids have a clear scale that must be kept clean to maintain their vision. This scale, like the rest of the lizard's external scales, is shed over time. The eyes of geckos are often marked with cryptic colours, allowing them to better camouflage themselves and avoid predators.
Geckos typically hide themselves under tree bark, in cavities, or other sheltered spaces when sleeping. Those without eyelids constrict their pupils as much as possible while sleeping. Geckos are mostly nocturnal, but some are diurnal, active during daylight hours. The shape of a gecko's pupil is related to its hunting style and activity period, with nocturnal species having elliptical pupils and diurnal species having round pupils.
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Lizards go through the same sleep stages as humans
Lizards, like humans, need a good night's sleep. While most geckos are nocturnal, some are diurnal and are active during the day. Geckos without eyelids constrict their pupils as much as possible when sleeping.
Scientists have discovered that lizards go through almost the same sleep stages as humans. Electrodes placed on the surface of five sleeping bearded dragons' brains recorded evidence of the lizards going through the stages of human slumber: slow-wave sleep, sharp waves, ripples and rapid eye movement (REM). This was a surprising finding because, until recently, scientists had only studied the brain activity of sleeping mammals and birds, not non-avian reptiles.
The discovery of similar sleep stages in lizards and humans sheds new light on how the architecture of sleep evolved. The data suggests that the two alternating stages of sleep, REM and slow-wave sleep, have an ancient origin. This could mean that parts of a lizard's brain associated with sleep are more ancient and that the origins of sleep can be traced back to earlier in the evolutionary tree.
However, while humans and lizards share similar sleep stages, the length of those cycles is not the same. A fast sleep cycle for a lizard is 80 seconds, while for humans, it is 60 to 90 minutes.
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Frequently asked questions
Lizards that don't have eyelids, such as geckos, sleep with their eyes open. However, they are still unconscious while sleeping.
Lizards have been found to go through similar sleep stages as humans, including slow-wave sleep, sharp waves, ripples, and REM sleep. However, the length of their sleep cycles differs, with a fast sleep cycle for a lizard lasting 80 seconds, compared to 30 minutes for a house cat and 60 to 90 minutes for humans.
While lizards experience similar neural activity during sleep as humans, it is unclear if they have complex dreams like humans do. Some researchers suggest that "bits of 'neuronal playback' in certain brain areas during sleep" could be considered dreams.
