Episode 199 – Hibernation

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Many animals have the ability to enter a period of dormancy to wait out difficult times. This episode, we discuss the various forms of Hibernation.

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A Long Rest

Many animals have the ability to enter a state of dormancy, during which their metabolic processes and certain bodily functions slow or stop. In some cases, dormancy might last only part of a day, while in others, it can go on for months. This dormant state is generally called torpor, though there are other terms used: diapause is a type of torpor seen in arthropods, brumation is long-term torpor exhibited by reptiles and amphibians, and the term hibernation typically refers to long-term dormancy in mammals.

The main benefit of torpor is the ability to wait out difficult conditions. Hibernating mammals famously power down for the winter, and the various forms of torpor can allow animals to limit their energy expenditure during certain times of the day, certain times of the year, or even certain events such as wildfires or storms. Some species undergo particularly extreme versions of this, such as frogs and insects that freeze completely during the winter or tardigrades which enter an extreme state of resilient dormancy called cryptobiosis.

Note that torpor and hibernation are different from sleep. In fact, hibernating animals can sometimes suffer sleep deprivation because it’s hard to hibernate and sleep at the same time!

Similar tactics are employed by non-animals, including plants whose seeds can remain dormant for months or years before sprouting, and bacteria who can form cysts to wait out difficult times.

Torpor can be tough to identify in the fossil record, but there are some potential clues. Regular periods of dormancy can leave signs of low activity in bones and teeth, which can be preserved in fossils; this sort of potential evidence of torpor has been noted in fossil ground squirrels (whose modern relatives hibernate) and in some early synapsids, the forerunners of true mammals.

The topic of hibernation and torpor are also relevant to mass extinctions. Animals who have the ability to go dormant for stretches of time might be more capable of surviving the difficult conditions during mass extinction events such as those at the end of the Permian and Cretaceous. There is some fossil evidence that suggests that species who are flexible in their energy needs and activity levels survived better through these extinction events.

Learn more

VIDEOS
Frogsicles: Frozen But Still Alive
Painted Turtles Defrost Back to Life | Frozen Planet II

These animals can freeze solid in winter. Here’s how they survive.

Hibernation (technical, open access)
More functions of torpor and their roles in a changing world (technical, open access)

Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica (technical, open access)
The cave bear’s hibernation: reconstructing the physiology and behaviour of an extinct animal (technical, paywall)

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If you enjoyed this topic and want more like it, check out these related episodes:

• Episode 161 – Sleep
• Episode 179 – Thermoregulation
• Episode 187 – Migration

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