BIOL 4010 Lecture Notes - Lecture 8: Barnacle Goose, Ground Squirrel, Torpor
2 May 2018
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Hibernation
Overview:
• Definitions and distinctions
• Metabolic mechanisms
• Physiological adaptations
• Climate change implications
• Comparative physiology within and among groups
Thermoregulation: Heterothermy
• Facultative Hypothermia (e.g. body temperature reduction)
o Shallow Hypothermia (seasonal hypothermia)
• Seasonally (typically during colder months)
• 1-5C reduction in body temp with no change in activity
• Observed in winter squirrels, barnacle geese
▪ Note: ground squirrels partake in deep hypothermia although they share the same
niche as red squirrels
o Rest-phase Hypothermia (torpor)
• Regular (<24 hr) decreases in body temperature and metabolic rate
• Coincides with regular period of inactivity
• Metabolic rate decreases, followed by a reduction in body temp
• The energy saved by torpor > energy cost of arousal
▪ Body temperature decreases during torpor but remains to normal during arousal
• Common in small birds and mammals
• Chickadees in winter:
▪ Body temp is 40-42C during day, and declines to 29C during the night
• Hummingbirds:
▪ During day has 39C body temperature, requires 0.24g of fat
▪ During night has 12-17C body temperature, requires 0.02 fat for fuel
▪ *see figure: O2 consumption vs Air temperature when aroused and in torpor
• Adaptive for animals with limited capacity for thermogenesis or insulation
o Deep Hypothermia (hibernation)
• Seasonal decrease in body temperature and metabolic rate
▪ Body temperature within 1C of ambient temperature
▪ Oxygen consumption 1/20th of regular rate
• True hibernation limited to mammals <5 kg
▪ Bears enter a winter 'dormancy'
• Body temperature decreased by ~5C
• Metabolic rate decreased by ~50-75%
• *largely debated whether they are hibernators
• Survive periods of food shortage, increase survival
*occurs in all three orders of mammals (including a primate) and 11 or 26 orders of birds
• Body temperature reduction in facultative hypothermia:
o Body temperature falls below 10C
o Metabolic rate is reduced by ~90%
o Obligate vs. facultative hibernators
• Obligate - deeply entrained with hibernating cues (will hibernate in lab)
• Facultative -
• Does torpor slow ageing?
o Decreased shortening of telomeres
o Prolonged reproductive age
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o Delayed senescence
o Longer lived
• Daily Torpor vs Hibernation
o Daily torpor: minimum body temperature between ~10-29C, with torpor bouts <24 hrs
o Hibernation: minimum body temperature <10C and torpor bouts of several days or weeks
o *both are adaptations to survive periods of low temperature or food scarcity
Hibernation in Belding's Ground Squirrels:
• As it gets colder, the body temperature of ground squirrels drops as they enter hiberation with bouts
of arousal throughout
• The metabolism also drops during hibernation but spikes during arousal bouts
• These animals save energy as additional metabolism that would be required to stay active in the
winter
• Note: bears do not defecate, move, or eat during
• Study: Golden Mantled Ground Squirrel
o Body temperature is relatively constant in summer
o Metabolic rate and temperature drop on a daily basis in autumn (matches drop in temperature
at night)
o In the winter, these animals hibernate, with a further decrease in body temperature after each
arousal
o During torpor, metabolic rates decrease to 2-5% of BMR
Understanding Hibernation
• Liver function
• Catabolism of stored energy
• Avoiding toxification
o Ischemia
o Urea
• Avoiding physical breakdown
o Muscle
o Bone
Mitochondrial Bioenergetics
• Oxidation creates energy to pump protons from the matrix to the IMS
• But only 40% of the energy is used, the rest is released as head
• Nonetheless, MR is suppressed during hibernation
• Brown fat cells (in BAT) generate heat using uncoupling protein
o UCP: futile cycling of H+, generates heat but no ATP
• Note: Cytochrome C levels are a measure of metabolic activity
Metabolic Rate Suppression
• Hypothesis 1 - turn off metabolism
o Succinate oxidation (beginning of ETC) is reduced in torpor, but only at high temperatures
o No difference at low temperatures
o Likely not simply inhibition of this first step in ETC
Liver Production of Bile:
• Example: Golden mantle ground squirrel
o No change in bile or cholesterol concentration
o Increased biliruben (cellular antioxidant) during torpid state
o pH of bile is much lower (more H+ ions) during torpid and inter-bout aroused stated
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Overview: definitions and distinctions, metabolic mechanisms, physiological adaptations, climate change implications, comparative physiology within and among groups. In the winter, these animals hibernate, with a further decrease in body temperature after each arousal: during torpor, metabolic rates decrease to 2-5% of bmr. Understanding hibernation: liver function, catabolism of stored energy, avoiding toxification. Ischemia: urea, avoiding physical breakdown, muscle, bone. Metabolic rate suppression: hypothesis 1 - turn off metabolism, succinate oxidation (beginning of etc) is reduced in torpor, but only at high temperatures, no difference at low temperatures, likely not simply inhibition of this first step in etc. Liver production of bile: example: golden mantle ground squirrel, no change in bile or cholesterol concentration. Increased biliruben (cellular antioxidant) during torpid state: ph of bile is much lower (more h+ ions) during torpid and inter-bout aroused stated. Avoid reperfusion injury: tissue damage is caused when oxygen levels return to normal after a period of ischemia (low oxygen)
