14.2 Hibernation, estivation, and torpor
4 min read•august 7, 2024
Animals have incredible ways to survive harsh conditions. and help them conserve energy during cold or dry periods. These strategies involve slowing down bodily functions and lowering .
is a short-term energy-saving trick used by some animals. It's like a mini-hibernation that can happen daily. plays a key role in keeping animals warm during these energy-saving states.
Hibernation and Estivation
Hibernation and estivation as survival strategies
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- Hibernation is a state of deep sleep that allows animals to conserve energy during periods of cold weather and scarce food resources
- Estivation is a similar state of dormancy that occurs during hot, dry periods when food and water are limited
- Both hibernation and estivation involve significant reductions in metabolic rate, body temperature, and other physiological functions
- Animals that hibernate or estivate include bears, ground squirrels, hedgehogs, and certain amphibians (frogs, salamanders)
Circannual rhythms and seasonal cues
- are endogenous biological cycles that occur on an annual basis and regulate hibernation and estivation
- These rhythms are synchronized with seasonal changes in environmental cues such as temperature, day length (), and food availability
- , a hormone secreted by the pineal gland, plays a crucial role in regulating circannual rhythms and preparing animals for hibernation or estivation
- Changes in melatonin levels in response to altered day length trigger physiological adaptations such as increased food intake and prior to hibernation
Arousal from hibernation and estivation
- is the process by which animals wake up from hibernation or estivation and return to normal metabolic and physiological functions
- Arousal can be triggered by external cues such as increasing temperature or internal factors such as depleted energy reserves
- During arousal, animals experience a rapid increase in body temperature, heart rate, and respiratory rate as they resume normal activity
- Periodic arousals during hibernation allow animals to restore cellular functions, eliminate metabolic wastes, and maintain neural connections
Torpor and Metabolic Depression
Torpor as a short-term energy-saving strategy
- Torpor is a state of reduced metabolic activity and body temperature that occurs on a daily or short-term basis
- Unlike hibernation and estivation, torpor is not necessarily associated with specific seasons or environmental conditions
- Animals enter torpor to conserve energy during periods of food scarcity, cold exposure, or other metabolic challenges
- Examples of animals that use torpor include , , and (dunnarts)
Metabolic depression and its physiological effects
- is a significant reduction in an organism's metabolic rate, often associated with torpor, hibernation, and estivation
- During metabolic depression, animals experience decreased , protein synthesis, and enzyme activity
- Metabolic depression allows animals to conserve energy by reducing the energy demands of various physiological processes
- The extent of metabolic depression varies among species, with some animals reducing their metabolic rate by up to 95% during hibernation or estivation
Hypothermia and supercooling in torpid animals
- is a state of low body temperature that occurs during torpor, hibernation, and estivation
- Torpid animals allow their body temperature to drop close to ambient temperature, minimizing the energy required to maintain a constant body temperature
- is a process by which animals can maintain their body fluids in a liquid state even at temperatures below the normal freezing point
- Some animals, such as the Arctic ground squirrel, can supercool their body fluids to temperatures as low as -2.9°C (26.8°F) during hibernation without causing tissue damage
Brown Adipose Tissue
Brown adipose tissue and its role in thermogenesis
- (BAT) is a specialized type of fat that is rich in mitochondria and plays a crucial role in (heat production)
- BAT is found in many mammals, particularly in newborns and hibernating species
- The primary function of BAT is to generate heat through the oxidation of fatty acids, helping animals maintain their body temperature in cold environments
- BAT is activated by the sympathetic nervous system in response to cold exposure or other stimuli
Mitochondrial uncoupling and heat production
- is a key mechanism by which BAT generates heat
- In BAT mitochondria, the protein thermogenin ( or UCP1) allows protons to leak across the inner mitochondrial membrane, bypassing ATP synthase
- This uncoupling of oxidative phosphorylation from ATP production results in the dissipation of energy as heat instead of ATP synthesis
- The activity of UCP1 is regulated by the sympathetic nervous system and thyroid hormones, allowing animals to modulate their heat production in response to environmental conditions
Nonshivering thermogenesis in mammals
- (NST) is the production of heat by means other than muscle shivering, primarily through the activity of BAT
- NST is particularly important for small mammals and newborns, who have a high surface area-to-volume ratio and are more susceptible to heat loss
- In addition to BAT, some mammals (cetaceans, pinnipeds) also utilize muscle-based NST, where heat is generated by the activity of sarcolipin, a protein that uncouples calcium transport from ATP hydrolysis in skeletal muscle
- NST allows animals to maintain their body temperature and metabolic functions in cold environments without relying on shivering, which is less efficient and more energy-intensive
Key Terms to Review (26)
Arousal: Arousal refers to a physiological and psychological state of being awake and responsive to stimuli, which can vary in intensity. It plays a crucial role in the survival strategies of animals, particularly in relation to behaviors like hibernation, estivation, and torpor, where energy conservation and metabolic regulation are essential. The level of arousal can influence how organisms respond to environmental changes and the necessity for periods of dormancy.
Bats: Bats are flying mammals belonging to the order Chiroptera, known for their ability to navigate and hunt using echolocation. These creatures play significant roles in their ecosystems, including pollination and pest control, and they exhibit unique adaptations for hibernation and sensory specialization that are crucial for their survival in various habitats.
Body temperature: Body temperature refers to the measure of the body's ability to generate and dissipate heat, maintaining a stable internal environment crucial for physiological processes. This balance is essential for homeostasis, and the regulation of body temperature is achieved through various physiological control systems and feedback mechanisms that respond to internal and external changes. Understanding body temperature is also key in explaining survival strategies like hibernation, estivation, and torpor, where organisms adapt their body temperature to survive extreme environmental conditions.
Brown adipose tissue: Brown adipose tissue (BAT) is a specialized type of fat tissue that plays a crucial role in thermogenesis, which is the process of heat production in organisms. Unlike white adipose tissue that stores energy, BAT is abundant in mitochondria and uncoupling protein 1 (UCP1), allowing it to burn calories to generate heat, especially in response to cold exposure. This function is vital for maintaining body temperature and energy balance, particularly in mammals during periods of environmental stress.
Brown fat tissue: Brown fat tissue, also known as brown adipose tissue, is a specialized type of fat that generates heat through a process called thermogenesis, particularly in response to cold exposure or during periods of hibernation. This tissue is rich in mitochondria and contains a high number of blood vessels, allowing it to produce energy efficiently and regulate body temperature. Brown fat plays a vital role in the energy metabolism of various mammals, especially those that enter states of reduced activity like hibernation, estivation, or torpor.
Cellular respiration: Cellular respiration is the biochemical process by which cells convert nutrients, primarily glucose, into energy in the form of adenosine triphosphate (ATP), while releasing waste products. This process is crucial for maintaining the energy balance within living organisms, allowing them to perform vital functions. In certain states like hibernation, estivation, and torpor, cellular respiration plays a significant role in energy conservation and metabolic rate adjustment to adapt to environmental conditions.
Circannual rhythms: Circannual rhythms are biological cycles that occur on an annual basis, influencing behaviors and physiological processes in many animals. These rhythms help organisms adapt to seasonal changes in their environment, regulating activities such as reproduction, hibernation, and migration. Understanding circannual rhythms is essential for grasping how animals interact with seasonal variations in temperature, food availability, and daylight.
Daily torpor: Daily torpor is a temporary state of decreased physiological activity and metabolic rate, commonly observed in small endothermic animals to conserve energy during periods of inactivity or unfavorable environmental conditions. This state is characterized by reduced body temperature, heart rate, and overall metabolic demands, allowing the animal to survive on limited energy reserves during times when food is scarce or temperatures drop.
Energy conservation: Energy conservation refers to the practices and processes that reduce energy consumption and optimize the use of available energy resources. In the context of certain physiological states, organisms adapt by lowering their metabolic rates and utilizing stored energy reserves, allowing them to survive adverse conditions when food is scarce or environmental factors are harsh.
Estivation: Estivation is a state of dormancy or inactivity that some animals enter during extreme heat or arid conditions, allowing them to survive unfavorable environmental conditions. This physiological adaptation helps organisms conserve water and energy, much like hibernation does for animals facing cold temperatures. Estivation is crucial for survival in habitats where food and water become scarce due to high temperatures.
Fat storage: Fat storage refers to the biological process of accumulating energy reserves in the form of lipids, primarily within adipose tissues. This process is essential for animals to survive periods of food scarcity, as it provides a readily available energy source during hibernation, estivation, and torpor, when metabolic rates significantly decrease.
Hibernation: Hibernation is a state of prolonged dormancy that some animals enter to survive extreme environmental conditions, particularly during cold months when food is scarce. During this time, metabolic rates significantly decrease, allowing animals to conserve energy and endure periods of harsh weather. Hibernation is crucial for the survival of many species, as it enables them to cope with drastic temperature changes and resource availability.
Hummingbirds: Hummingbirds are small, agile birds known for their vibrant colors and unique ability to hover in mid-air by rapidly flapping their wings. They are fascinating examples of extreme adaptation, especially regarding energy metabolism, as they are often seen feeding on nectar from flowers. Their remarkable flight capabilities and energetic lifestyle connect them to various physiological processes, particularly in the context of hibernation, estivation, and torpor, as they must manage energy expenditure and maintain survival during adverse conditions.
Hypothermia: Hypothermia is a medical condition that occurs when the body's core temperature drops below the normal range, typically defined as below 35°C (95°F). This condition can lead to severe physiological disruptions, as the body loses its ability to maintain normal metabolic functions and thermoregulation. Understanding hypothermia is crucial for grasping how animals cope with extreme cold environments and adapt their energy balance during states of decreased metabolic activity.
Melatonin: Melatonin is a hormone produced by the pineal gland that regulates sleep-wake cycles and circadian rhythms. It plays a key role in signaling the body when it is time to sleep, especially in response to darkness, and influences various physiological processes related to seasonal changes in behavior, such as hibernation and reproduction.
Metabolic Depression: Metabolic depression is a physiological state characterized by a significant reduction in metabolic rate, allowing organisms to conserve energy during periods of environmental stress or unfavorable conditions. This adaptive response is commonly observed in various animals during hibernation, estivation, and torpor, helping them survive when resources are scarce or environmental temperatures are extreme.
Metabolic rate reduction: Metabolic rate reduction refers to the significant decrease in an organism's metabolic processes, leading to lower energy expenditure. This adaptive physiological response is crucial for survival during periods of environmental stress, such as extreme temperatures or food scarcity, allowing organisms to conserve energy and resources. By entering states like hibernation, estivation, or torpor, animals can effectively lower their metabolic rates and maintain homeostasis while minimizing the need for food intake.
Mitochondrial uncoupling: Mitochondrial uncoupling refers to the process where the proton gradient generated during oxidative phosphorylation is dissipated, leading to a decrease in ATP production and an increase in heat generation. This phenomenon is significant in various metabolic processes, especially during states like hibernation and torpor, where energy conservation and thermogenesis play crucial roles in survival under extreme environmental conditions.
Nonshivering thermogenesis: Nonshivering thermogenesis is the process by which organisms generate heat without muscle contractions, primarily through metabolic processes in brown adipose tissue. This mechanism is particularly important for maintaining body temperature in cold environments and plays a critical role in thermoregulation during states of reduced metabolic activity such as hibernation, estivation, and torpor.
Photoperiod: Photoperiod refers to the duration of light and dark periods within a 24-hour cycle that organisms experience, influencing their behavior and physiological processes. It plays a crucial role in regulating seasonal activities, such as hibernation, estivation, and torpor, as well as circadian rhythms and biological clocks that help organisms adapt to their environment. The changes in photoperiod can signal to animals when to migrate, breed, or enter dormancy.
Small marsupials: Small marsupials are a diverse group of mammals characterized by their unique reproductive system, where females give birth to relatively undeveloped young that continue to grow in a pouch. This group includes species like quokkas, bandicoots, and sugar gliders, which exhibit various adaptations for survival in their specific environments.
Supercooling: Supercooling is the process in which a liquid is cooled below its freezing point without it becoming solid. This phenomenon is particularly important in the context of various physiological adaptations that allow certain animals to endure extreme environmental conditions, such as freezing temperatures during periods of dormancy.
Survival Strategy: A survival strategy refers to the specific behaviors and physiological adaptations that organisms employ to cope with environmental challenges and enhance their chances of survival. These strategies can include mechanisms for energy conservation, resource allocation, and responses to unfavorable conditions. In the context of hibernation, estivation, and torpor, survival strategies help organisms endure periods of extreme temperatures or limited food availability by entering states of reduced metabolic activity.
Thermogenesis: Thermogenesis is the process of heat production in organisms, essential for maintaining body temperature and metabolic functions. It plays a crucial role in energy balance by converting stored energy into heat, which is especially important for endothermic animals that regulate their body temperature internally. This process is influenced by various factors including hormonal regulation, environmental conditions, and physiological states such as activity level and metabolic demands.
Torpor: Torpor is a state of decreased physiological activity in animals, characterized by reduced metabolic rate, lowered body temperature, and decreased responsiveness to external stimuli. This adaptation allows animals to conserve energy during periods of unfavorable environmental conditions or when food is scarce, connecting it closely to survival strategies in extreme environments as well as hibernation and estivation patterns.
Uncoupling Protein 1: Uncoupling Protein 1 (UCP1) is a mitochondrial protein found predominantly in brown adipose tissue that plays a crucial role in thermogenesis by dissipating the proton gradient generated by the electron transport chain. This protein enables non-shivering thermogenesis, allowing organisms to produce heat instead of ATP in response to cold exposure or overfeeding, thus regulating body temperature and energy balance.