MFWB_A - Hibernation

difference between large and small animals in cold climates

large limit heat loss, small need to find ways to reduce energy usage

obligate migration

all animals migrate to usually the same general areas

irruptive migration

opportunistic migrations determined by local conditions

partial migration

part of population stays behind

subnivean zone

insulated by heavy snow on top, around 0, small animals - some stay all winter, some overnight or during bad weather,

lemmings

do not hibernate or enter torpor, their numbers are correlated to the previous year’s snow

fur, fat and feathers insulation

vasoconstriction, insulate due to how well their hair holds air

blubber insulation

food store and streamlining, can be up to 50% of the animal’s weight, connected to muscles and skeleton by tendons and ligaments, composition changes from inside to outside - to retain physical properties of lipids

torpor

short periods of inactivity, reduced metabolic rate and body temperature, e.g, some hummingbirds, marsupials, rodents

hibernation

prolonged reduction of activity, decreased metabolic rate, heart rate and body temperature, e.g, some mammals, rodents, bears

aestivation

avoid excessive heat and drought, e.g, fat tailed dwarf lemur

torpor and hibernation costs

increased predation, long-term memory loss?, decreased immune function?

arousal from torpor and hibernation

metabolism increases higher than normal

Brown adipose tissue function

generates heat with 10-fold efficiency compared to shivering, unique to mammals, uses uncoupling proteins to generate heat rather than ATP, fat rich with high densities of mitochondria

thermogenin

changes function of mitochondria in BAT so energy is dissipated as heat instead of energy

bat migration

torpor assisted, silver-haired bats, save up to 91% of resting energy needs, have smaller brains (more space for nutrients)

bat hibernation

limited in their possible mass increase before migration due to being aerial predators, relatively high metabolism, white-nose syndrome thrives in hibernating groups

extreme hibernation

e.g, arctic ground squirrels hibernate from September to may, core temperature can drop to -2.9 but brain at 0, potential to cleanse their blood of ice nucleators so not freezing, allow squirrels to lower annual metabolic rates to manageable level due to scarce food sources

bear hibernation

up to 7 months no food, drink, urination or defaecation, no osteoporosis, give birth to highly altricial cubs - females lose 50% of body weight from milk, urea cycle - instead recycled and resynthesised into skeletal muscle and proteins, wound healing occurs, saved up body fat supplies substrate (400 kcal/day) metabolic water sustains hydration, urine filtered by kidneys but bladder wall transports water and solute back into blood

aestivation

avoid drought, body temperature can fluctuate as much as 25 in one day, save around 70%