Response to cold Response to cold environments: Freeze environments: Freeze avoidance vs. Freeze avoidance vs. Freeze tolerancetolerance

Dealing with cold—Dealing with cold—MammalsMammals Increase Increase

insulationinsulation Decrease heat Decrease heat

lossloss Increase Increase

metabolismmetabolism Decrease Decrease

metabolic costsmetabolic costs

Increase insulationIncrease insulation

FurFur FatFat Size Size BurrowingBurrowing

Decrease heat lossDecrease heat loss

VasoconstrictionVasoconstriction

PiloerectionPiloerection

Countercurrent exchangeCountercurrent exchange

Increase metabolismIncrease metabolism

Physiological Thermogenesis: Physiological Thermogenesis: – Basal Metabolic Rate (BMR)Basal Metabolic Rate (BMR)

Produces heat and ATPProduces heat and ATP

– Shivering thermogenesisShivering thermogenesis Non-synchronous contraction of skeletal muscle Non-synchronous contraction of skeletal muscle

– Non-shivering thermogenesis (NST)Non-shivering thermogenesis (NST) Brown adipose tissue (BAT)Brown adipose tissue (BAT)

MetabolismMetabolismmaxmax = BMR + NST + = BMR + NST + shiveringshivering

Temperature and Temperature and metabolic ratemetabolic rate

Torpor and Torpor and HibernationHibernation TorporTorpor=naturally occurring drop in T=naturally occurring drop in Tb b

(body temp) with resulting drop in (body temp) with resulting drop in metabolism, circulation, and respiratory metabolism, circulation, and respiratory ratesrates

Who uses torpor?Who uses torpor?– Birds, reptiles, amphibians, mammalsBirds, reptiles, amphibians, mammals

How is torpor different from hypothermia?How is torpor different from hypothermia?– Core temperature defended at low level in torporCore temperature defended at low level in torpor– Time taken to arouseTime taken to arouse

– Euthermia=normal warm TEuthermia=normal warm Tbb

Torpor and Torpor and Hibernation (cont)Hibernation (cont) Estivation=torpor bouts in summerEstivation=torpor bouts in summer HibernationHibernation=multi-day torpor bouts =multi-day torpor bouts

in winterin winter– Endothermy NOT abandoned—Endothermy NOT abandoned—regulateregulate

temp at lower leveltemp at lower level

HibernationHibernation

How developed?How developed?– Ancestral conditionAncestral condition– Evolved separately in birds and mammalsEvolved separately in birds and mammals

Why do only some members of each Why do only some members of each group hibernate?group hibernate?– SizeSize– Resource availabilityResource availability

‘‘True’ hibernation vs. ‘winter lethargy’True’ hibernation vs. ‘winter lethargy’– True hibernators are smaller, drop Tb to close True hibernators are smaller, drop Tb to close

to ambient, bouts last several daysto ambient, bouts last several days– Winter lethargy (bears, carnivores)—temp Winter lethargy (bears, carnivores)—temp

drops a few degrees, bouts last weeks-monthsdrops a few degrees, bouts last weeks-months

Winter (Oct-Mar): Animals enter

hibernation, drop Tb to near Ta, drop metabolic

rate, start burning fat reserves

Spring (Mar-May): Arousal—males first, then females; mating, parturition, start replacing body

mass lost

Summer (May-Aug): Continue feeding to build fat, sunning to help store fat,

juveniles mature

Fall (Aug-Oct): Major fat-building

(lipogenic) period--pack on as much fat as possible,

prepare burrows for winter

The Hibernation Cycle:The Hibernation Cycle:

Hibernation (cont)Hibernation (cont)

A typical torpor bout (marmot):A typical torpor bout (marmot):– Animal drops Tb to near Ta, slows Animal drops Tb to near Ta, slows

metabolism (2-6 hours) metabolism (2-6 hours) Respiration, heart, metabolic rates dropRespiration, heart, metabolic rates drop Synapses separate in brain—brain dead!Synapses separate in brain—brain dead!

– Animal remains at low tissue temp (6-8 days)Animal remains at low tissue temp (6-8 days) Metabolic process occur at very low levelsMetabolic process occur at very low levels

– Animal returns to euthermic temperature (1-2 Animal returns to euthermic temperature (1-2 hours)hours)

Synapses re-grow, metabolic & cardiovascular Synapses re-grow, metabolic & cardiovascular rates speed up, animal becomes activerates speed up, animal becomes active

GSM-5-05 Cold

05

1015202530354045

10

/14

/20

05

10

/23

/20

05

11

/01

/20

05

11

/10

/20

05

11

/19

/20

05

11

/28

/20

05

12

/08

/20

05

12

/17

/20

05

12

/26

/20

05

01

/04

/20

06

01

/13

/20

06

01

/22

/20

06

01

/31

/20

06

02

/09

/20

06

02

/18

/20

06

02

/27

/20

06

03

/08

/20

06

03

/17

/20

06

03

/27

/20

06

Date

Bo

dy

Te

mp

(c

)

A B C D

Typical hibernation seasonTypical hibernation season

Obesity and Obesity and hibernationhibernation Obesity=excessive accumulation Obesity=excessive accumulation

of body fatof body fat– Generally considered pathogenicGenerally considered pathogenic– Diabetes, atherosclerosis, Diabetes, atherosclerosis,

osteoarthritisosteoarthritis Hibernating animals become fat Hibernating animals become fat

without associated pathologieswithout associated pathologies– Hormone pathway blockingHormone pathway blocking– Time span/seasonality of obesityTime span/seasonality of obesity

Model AnimalsModel Animals

Golden-mantled ground Golden-mantled ground squirrels (GMGS)squirrels (GMGS)– Spermophilus lateralisSpermophilus lateralis– Summer weight 150 gSummer weight 150 g– Winter weight 350 gWinter weight 350 g

Yellow-bellied marmotsYellow-bellied marmots– Marmota flaviventrisMarmota flaviventris– Summer weight 2 kilosSummer weight 2 kilos– Winter weight 5 kilosWinter weight 5 kilos

– Marmota monaxMarmota monax– Summer weight 2 kilosSummer weight 2 kilos– Winter weight 5 kilosWinter weight 5 kilos

What can we measure?What can we measure?

Body temperature (implanted data Body temperature (implanted data loggers, temp tracking radio loggers, temp tracking radio collars)collars)

Hormone levels (factors in obesity, Hormone levels (factors in obesity, food intake)food intake)

Dietary choices (energy levels, Dietary choices (energy levels, fatty acids for membrane fluidity)fatty acids for membrane fluidity)

Behavior (constrained by food Behavior (constrained by food intake, dietary choices)intake, dietary choices)