Physiology of hibernation,

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1 Physiology of hibernation, aestivation and diapause. BIOS 0903A; Gr. A

innervated by the sympathetic nervous system Sympathetic

2 BAT This is a specialized type of adipose tissue often reddish brown BAT receive a rich supply of blood vessels and are well innervated by the sympathetic nervous system Sympathetic nervous system releases norepinephrine BAT increases oxidation = more heat

Birth at tundra At the time of birth of a reindeer (Rangifer tarandus) calf In uterio: 37 C Ambient: ~ 0 C They are born with thick fur covering They are able to raise their rate of metabolic heat

3 Birth at tundra At the time of birth of a reindeer (Rangifer tarandus) calf In uterio: 37 C Ambient: ~ 0 C They are born with thick fur covering They are able to raise their rate of metabolic heat production to at least twice their resting rate Brown fat is nearly always the principal thermogenictissue in newborn placental mammals, and NST is thus the principal mechanism of thermogenesis in newborns

4 What about small mammals? The white-footed mouse (Peromyscus leucopus), one of the most abundant native small mammals in North America, provides a typical example of the course of development. In the days immediately following birth, young white-footed mice can respond to cold exposure by increasing their metabolic rates to a small extent, and if all the young in a litter huddle together within the nest their mother provides, they are able collectively to thermoregulate reasonably well for a few hours even when the air outside the nest is near freezing. Brown fat is present at birth. But the trajectory of brown-fat development in small mammals is extremely different from the trajectory in large mammals. In reindeer and sheep, brown fat is maximally or near maximally developed at birth, and it starts to wane soon after birth, so it is gone or approximately gone by about a month of age. In small mammals such as mice and rats, by contrast, brown fat is far from fully developed at birth, and during much of the first month of life, it develops an ever-greater thermogenic ability.

5 We are still discussing spring to fall in tundra and NOT winter

6 The winter strategy Large mammals 1. Can t hide and have to be present on the surface 2. Because of their size, reindeer have a surface-to-volume ratio that is favorable for retaining heat in cold environments 3. Can t huddle 4. Migration is a significant strategy Small mammals 1. Lemmings in the Arctic and pikas in the high mountains are able to escape the biting cold and howling winds of the larger environment by living under the snow or in other protective hideaways 2. Surface-to-volume ratio is high, less heat retention 3. Can huddle 4. Can t migrate

7 Hibernation The great majority of hibernators have adult body sizes of 5 kg or less. energy savings afforded by hibernation decline with body size

8 As a strategy Among species of mammals that weigh 5 kg or less, hibernation is not at all universal. In the Arctic, for example, whereas ground squirrels hibernate, lemmings and flying squirrels do not. We do not understand why species have diverged in these ways. At our present level of understanding, we can only conclude that the two modes of dealing with the cold of winter hibernating and staying active must each have pros and cons for small and medium-sized mammals. Neither strategy is so obviously better that it has become universal.

9 Arctic ground squirrel kg, Lives in Alaska, lives and hibernates in a burrow that has to be less than 1 m below the surface (permafrost boundary).

Hibernating ground squirrel Their hibernacula can have ambient temperate as low as -25 C Scientists used to believe that hibernation continued throughout winter Now radiotelemetric data shows that

10 Hibernating ground squirrel Their hibernacula can have ambient temperate as low as -25 C Scientists used to believe that hibernation continued throughout winter Now radiotelemetric data shows that animal arousal is periodic and universal Continuous periods of hypothermia lasted 1 3 weeks. Between those bouts of hibernation, the ground squirrel raised its body temperature to C for h during each arousal.

Hibernation metabolism The rate of heat production of a hibernating ground squirrel is increased, as needed, by brown-fat thermogenesis to keep a different endothermic condition When the ambient

11 Hibernation metabolism The rate of heat production of a hibernating ground squirrel is increased, as needed, by brown-fat thermogenesis to keep a different endothermic condition When the ambient temperature (T A ) is above 0 C ground squirrel uses less metabolic energy (black line) to raise body temperature (T B ) high (blue line) When T A is less than 0 C more metabolism (BAT) is required to keep T B above 0 C Keep in mind the freezing point of the body fluids of Arctic ground squirrels remains the same during winter as it is in summer: 0.6 C (the typical value for mammals)

Food In addition to brown fat animals also store white fat in adipocyte White fat can be saturated (SFA), mono (MUFA) or poly unsaturated fatty acids (PUFA) SFA is solid at low

12 Food In addition to brown fat animals also store white fat in adipocyte White fat can be saturated (SFA), mono (MUFA) or poly unsaturated fatty acids (PUFA) SFA is solid at low temperature (think about butter at fridge) but PUFA is less so So the hibernating animals prefer food with PUFA than non hibernating animals Keep in mind, animals can t synthesize PUFA

Periodic arousal is expensive Suppose that these ground squirrels would use 100 units of energy without hibernation With hibernation they actually use 12 units of

13 Periodic arousal is expensive Suppose that these ground squirrels would use 100 units of energy without hibernation With hibernation they actually use 12 units of energy. However, of 12 units, 10 are for their periodic arousals. Without arousal they would energy would be 2 units. That is more than 80% is used for periodic arousals!

14 So, why arousals? Don t know but Hypothesis 1: Animals need to wake up to urinate. Then goldenmantled ground squirrels, blood urea concentration does not increase, but declines, during a bout of hibernation Hypothesis 2: Animals wake up to sleep. Brain wave for sleep and hibernation are different. Hypothesis 3: Animals need to reestablish brain dendrites and synapses Hypothesis 4: Hypothermia leads to immunosuppression and arousal activates immunity Keep in mind, all of the above hypotheses are based on some scientific observation but nothing is yet consensus

15 Sociobiology & hibernation physiology On average, in species of hibernating small mammals, an individual is about five times more likely to die in a month when it is active than when it is hibernating Scientists have observed three insectivorous bats (hoary bats, Lasiurus cinereus) in advanced pregnancy enter deep hibernation for 3 6 days during cold late-spring weather. They exit hibernation up to give birth In wild populations of ground squirrels, the males emerge from hibernation many weeks before the females. Hibernations slows down testicular development and require elevated body temperature for periods to have functional testes

16 Social hibernation Alpine marmots, for example, live throughout the year in social groups. A typical social group of alpine marmots consists of a dominant male and female and an assemblage of related, younger animals of various ages (up to several years old). All these animals hibernate together, in sets that number up to 20 individuals Social hibernation in alpine marmots has been shown to increase each individual s probability of overwinter survival, particularly among the young-of-the-year, termed juveniles

17 Torpor

18 Some facts on torpor Most heterolhermic mammals and birds appear to use one of two common patterns of torpor: (a) hibernation or prolonged. multiday torpor is employed by the "hibernators," and (b) daily torpor is employed by the "daily heterotherms." In diurnal species. such as many birds, daily torpor is usually restricted to the night, whereas in nocturnal mammals and birds it is common in the second pan of the night and or the early morning. Less seasonal and can be because of food shortage And sometimes used when food is plenty Excessive fattening is limited

Winter Ecology Mammalian Adaptations to Winter Study Worksheet KEY and Fun Facts Sheryn Olson, University of Colorado, Mountain Research Station

I. Concepts Winter Ecology Mammalian Adaptations to Winter Study Worksheet KEY and Fun Facts Sheryn Olson, University of Colorado, Mountain Research Station 1. Energy Balance: Purpose is maintenance of