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Hibernation: the story on HearLore | HearLore
Hibernation
In the winter of 1900, Russian peasants in the Pskov Government engaged in a practice known as Lotska, spending six months sleeping around a stove, waking only once a day to consume bread and water, a human ritual that mirrors the deep dormancy of animals. This historical anecdote reveals that the concept of hibernation is not merely a biological curiosity but a survival strategy that has touched human history, even if only in the most desperate of circumstances. The term hibernation describes a state of minimal activity and metabolic reduction entered by some animal species to pass through winter months, a period often called overwintering. It is a seasonal heterothermy characterized by low body temperature, slow breathing, and heart rate, allowing creatures to conserve energy when food is scarce. While traditionally reserved for deep hibernators like rodents, the definition has expanded to include bears and other species based on active metabolic suppression rather than any absolute decline in body temperature. This shift in understanding has transformed how scientists view the animal kingdom, revealing that the line between sleep and hibernation is far more porous than previously thought.
Obligate And Facultative Strategies
Obligate hibernators are animals that spontaneously and annually enter hibernation regardless of ambient temperature and access to food, a trait seen in many species of ground squirrels, European hedgehogs, and monotremes. These creatures undergo a physiological state wherein the body temperature drops to near ambient temperature, and heart and respiration rates slow drastically. The typical winter season for these animals is characterized by periods of torpor interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals have plagued researchers for decades, with one favored hypothesis suggesting that hibernators build a sleep debt and must occasionally warm up to sleep. Evidence from the Arctic ground squirrel supports this, showing that hibernating individuals may exhibit abdominal temperatures as low as minus 2 degrees Celsius, maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 degrees Celsius or above. In contrast, facultative hibernators enter hibernation only when cold-stressed or food-deprived, a strategy exemplified by the chipmunk, which sleeps for a long period but does not truly hibernate unless food is scarce. The white-tailed prairie dog is an obligate hibernator, while the closely related black-tailed prairie dog is a facultative hibernator, highlighting the diversity of survival strategies within the same family.
What is the historical practice of Lotska among Russian peasants in the Pskov Government?
The historical practice of Lotska involved Russian peasants in the Pskov Government spending six months sleeping around a stove during the winter of 1900. They woke only once a day to consume bread and water, creating a human ritual that mirrors the deep dormancy of animals.
When was the discovery of hibernation in the fat-tailed dwarf lemur of Madagascar made?
The discovery of hibernation in the fat-tailed dwarf lemur of Madagascar occurred when researchers found the animal hibernates in tree holes for seven months of the year. This finding proved that hibernation is not exclusively an adaptation to low ambient temperatures, as Malagasy winter temperatures sometimes rise to over 30 degrees Celsius.
What year did research refute the theory that bear sleep is not comparable to true hibernation?
Research in 2011 on captive black bears and again in 2016 on brown bears refuted the theory that their deep sleep was not comparable to true hibernation. These studies showed that hibernating bears are able to recycle their proteins and urine, allowing them to stop urinating for months and avoid muscle atrophy.
Which species of shark was shown to travel long distances throughout the seasons instead of becoming dormant?
Research by David Sims in 2003 dispelled the hypothesis that basking sharks settled to the floor of the North Sea and became dormant. The study showed that the sharks traveled long distances throughout the seasons, tracking the areas with the highest quantity of plankton.
What is the earliest suggested instance of hibernation in the fossil record?
The earliest suggested instance of hibernation is in Thrinaxodon, an ancestor of mammals that lived roughly 252 million years ago. This species represents the transition from ectothermy to endothermy where ancestors of birds and mammals likely experienced an early form of torpor or hibernation.
For a long time, no primate or tropical mammal was known to hibernate until the discovery of hibernation in the fat-tailed dwarf lemur of Madagascar, which hibernates in tree holes for seven months of the year. Malagasy winter temperatures sometimes rise to over 30 degrees Celsius, proving that hibernation is not exclusively an adaptation to low ambient temperatures. The hibernation of this lemur is strongly dependent on the thermal behavior of its tree hole; if the hole is poorly insulated, the lemur's body temperature fluctuates widely, passively following the ambient temperature, but if well insulated, the body temperature stays fairly constant and the animal undergoes regular spells of arousal. This discovery challenged the notion that hypometabolism in hibernating animals is necessarily coupled with low body temperature. Similarly, the status of bears as true hibernators was contested until research in 2011 on captive black bears and again in 2016 on brown bears refuted the theory that their deep sleep was not comparable to true hibernation. Historically, it was unclear whether bears truly hibernate since they experience only a modest decline in body temperature of 4 to 5 degrees Celsius, compared with the much larger decreases often seen in other hibernators. Despite this, hibernating bears are able to recycle their proteins and urine, allowing them to stop urinating for months and to avoid muscle atrophy, staying hydrated with the metabolic water produced in sufficient quantities to satisfy their needs.
Frozen Lives And Hypoxic Survival
Ectothermic animals, including fish, reptiles, and amphibians, cannot engage in obligate or facultative hibernation because they cannot actively down-regulate their body temperature or metabolic rate. Instead, they experience decreased metabolic rates associated with colder environments or low oxygen availability, a state known as brumation. It was once thought that basking sharks settled to the floor of the North Sea and became dormant, but research by David Sims in 2003 dispelled this hypothesis, showing that the sharks traveled long distances throughout the seasons, tracking the areas with the highest quantity of plankton. However, other species have evolved remarkable survival mechanisms, such as the epaulette shark, which can survive for three hours without oxygen and at temperatures of up to 35 degrees Celsius. Some animals can survive winter by freezing, utilizing antifreeze proteins to naturally freeze and then wake up in the spring. Species like the wood frog and the red-eared slider have evolved freeze tolerance mechanisms, while the Antarctic yellowbelly rockcod suppresses its metabolism in hypoxic conditions. The ability to survive hypoxic or anoxic conditions is not closely related to endotherm hibernation, yet it represents a parallel evolutionary path to surviving the harshness of winter dormancy.
The Science Of Induction
Hibernation induction trigger proteins isolated from mammals have been used in the study of organ recovery rates, offering potential applications in medicine and space travel. One study in 1997 found that delta 2 opioid and hibernation induction trigger proteins were not able to increase the recovery rate of heart tissue during ischemia, yet the protein precursors were identified to play a role in the preservation of veterinary organ function. Recent advances in recombinant protein technology make it possible for scientists to manufacture hibernation induction trigger proteins in the laboratory without the need for animal euthanasia. Bioengineering of proteins can aid in the protection of vulnerable populations of bears and other mammals that produce valuable proteins. Protein sequencing of hibernation induction trigger proteins, such as alpha 1-glycoprotein-like 88 kDa hibernation-related protein HRP, contributes to this research pool. A study in 2014 used recombinant technology to construct, express, purify, and isolate animal proteins outside the animal to study key hibernation proteins. This research holds promise for saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given, and for enabling long-duration space travel to destinations like Mars.
Evolutionary Roots And Seasonal Pressures
As the ancestors of birds and mammals colonized land, leaving the relatively stable marine environments, more intense terrestrial seasons began playing a larger role in animals' lives. Hibernation of endothermic animals has likely evolved multiple times, at least once in mammals and at least once in birds, with the earliest suggested instance of hibernation being in Thrinaxodon, an ancestor of mammals that lived roughly 252 million years ago. The evolution of endothermy allowed animals to have greater levels of activity and better incubation of embryos, among other benefits for animals in the Permian and Triassic periods. In order to conserve energy, the ancestors of birds and mammals would likely have experienced an early form of torpor or hibernation when they were not using their thermoregulatory abilities during the transition from ectothermy to endothermy. This is opposed to the previously dominant hypothesis that hibernation evolved after endothermy in response to the emergence of colder habitats. Body size also had an effect on the evolution of hibernation, as endotherms which grow large enough tend to lose their ability to be selectively heterothermic, with bears being one of the very few exceptions. After torpor and hibernation diverged from a common proto-hibernating ancestor of birds and mammals, the ability to hibernate or go through torpor would have been lost in most larger mammals and birds.
Reptiles And Arthropod Dormancy
Reptilian winter dormancy, or brumation, likely evolved to help reptiles survive colder conditions, with reptiles that are dormant in the winter tending to have higher survival rates and slower aging. Reptiles evolved to exploit their ectothermy to deliberately cool their internal body temperatures, seeking out colder temperatures based on a periodic internal clock triggered by cooler outside temperatures, as shown in the Texas horned lizard. One mechanism that reptiles use to survive hibernation, hypercapnic acidosis, is also present in mammal hibernation, likely an example of convergent evolution. Hypercapnic acidosis evolved as a mechanism to slow metabolism and also interfere with oxygen transport so that oxygen is not used up and can still reach tissues in low oxygen periods of dormancy. Seasonal diapause in arthropods seems to be plastic and quickly evolving, with large genetic variation and strong effects of natural selection present. It evolved after the increased influence of seasonality as arthropods colonized terrestrial environments as a mechanism to keep energy costs low, particularly in harsher than normal environments. It is thought to have originally evolved in three stages: the development of neuroendocrine control over bodily functions, the pairing of that to environmental changes, and the pairing of these controls with reliable seasonal indicators within the arthropod, like biological timers.
Human Hibernation And Future Horizons
Researchers have studied how to induce hibernation in humans, with the ability to hibernate being useful for saving the lives of seriously ill or injured people by temporarily putting them in a state of hibernation until treatment can be given. For space travel, human hibernation is also under consideration, such as for missions to Mars. Anthropologists are also studying whether hibernation was possible in early hominid species, exploring the possibility that our ancestors may have utilized similar survival strategies. The historical practice of Lotska among Russian peasants in the Pskov Government, described in The British Medical Journal in 1900, serves as a reminder that human attempts to mimic hibernation have existed for centuries. While most animals that go through winter dormancy lower their metabolic rates, some fish, such as the cunner, do not, instead simply reducing their activity level. Fish that undergo winter dormancy in oxygenated water survive via inactivity paired with the colder temperature, which decreases energy consumption, but not the base metabolic rate that their bodies consume. The mechanism for evolution of metabolic suppression in fish is unknown, yet it represents another facet of the complex evolutionary history of dormancy.