How do mammals deal with cold? AVOIDANCE RESISTANCE Methods of Energy Conservation Methods of Energy Expenditure

Foraging zones: zones which have a much higher temperature than the outside air snow (insulation) ground air subnivean zone heat water vapor condenses & freezes forming pockets of space SUBNIVEAN ZONE stays about 32  C as long as the snow is > 6 inches deep regardless of air temp

Foraging zones: mammals often forage in zones which have a much higher temperature than the outside air snow ground air subnivean zone will be much colder if snow cover is light More snow can be better than less snow for small mammals

Food Hoarding Easily accessible food source during cold periods -cuts down search time outside of nest etc. Scatter-hoarders -scatter food around (use scent, memory to find) food example: southern flying squirrel

Food Hoarding Easily accessible food source during cold periods -cuts down search time (time outside of nest etc.) Larder-hoarder -make one or few big stashes (need to protect this) -example: chickaree

Food Hoarding Easily accessible food source during cold periods -cuts down search time (time outside of nest etc.) Predators -may stash big kills in snow for later

Torpor -can occur on a daily basis -form of dormancy lowering of: -body temp -metabolic rate -respiration -heart rate (not as drastic as hibernation) metabolic rate and body temp of Peromyscus during daily torpor Torpid by day, active by night

prolonged winter torpor Richardson’s ground squirrel 8 months of hibernation Normal body temp = 38ºC hibernation: probably accomplished by supercooling, where solutes build up in blood, lowering freezing temp of the blood hibernating body temp= 3º- 4ºC

How do mammals deal with cold? AVOIDANCE Body size Insulation Modification of microclimate regime -communal nesting -foraging zones Food hoarding Reduction in body mass Reduction in level of activity Dormancy Increase in thermogenic capacity RESISTANCE Energy Conservation Energy Expenditure

Resistance to Cold Shivering thermogenesis Non-shivering thermogenesis (NST) Brown adipose tissue -lots of mitochondria - acts as miniature internal blanket that overlies parts of the vascular system & heats blood Brown adipose (fat) tissue Thermogenin = special protein in brown adipose that the mitochondria produce heat instead of ATP

Flying squirrels

Make sure you do the reading and understand this figure for the exam

~35% of the Earth is covered by deserts Adaptations to heat

Variety of different types “deserts”

Adaptations to heat To survive in deserts mammals must cope with many demanding environmental challenges: -intense heat during day -paucity of water -very cold at night -little cover -highly variable food supply -challenges often more severe than those faced by animals in very cold environments Temperature & Water Regulation

Desert mammals must find ways to: DISSIPATE HEAT or AVOID HEAT CONSERVE WATER ADAPTATIONS -Anatomical -Physiological -Behavioral

millions of nephrons in medulla of each kidney -relatively large medulla -long loops of Henle -papilla extend into ureter To concentrate urine:

Loops of Henle found primarily in the medulla portion of the kidney -this portion is very prominent in kidneys of desert-dwelling mammals the papilla of the medulla are also enlarged in desert mammals

papilla small papilla very large papilla larger very wet wet dry

Strategies for conserving water -highly concentrated milk ( ~50% H2O ) Dipodomys merriami -highly concentrated urine & feces -mother consumes the relatively dilute urine & feces of young regain ~1/3 of water originally secreted in the milk

Diet -because free drinking water often limited or absent, many mammals rely on water stored in food -succulent plants -body fluids of prey Onychomys torridus (Grasshopper mouse) eating a grasshopper Neotoma albigula ( White-throated Woodrat) eating Opuntia (prickly pear cactus)

Diet -because free drinking water often limited or absent, many mammals rely on water stored in food metabolic water Arizona pocket mouse (Perognathus amplus) diet 95% seeds 1. Storing seeds in moist burrow allows seeds to gain moisture 2, Eat seeds high in carbohydrates -yield lots of water when they are oxydized

Diet Altriplex (Saltbush) Entire Atriplex leaves are consumed during the spring, but during the rest of the year only the inner, less saline tissues are utilized. -lower incisors chisel-shaped Chisel-toothed kangaroo rat Dipodomys microps

Diet Oryx (Oryx beisa) -Oryx can survive in environment often 40ºC+ -Primarily eat grasses & shrubs, especially the shrub Diasperma. -Diasperma leaves fluctuate in water content DAY: high heat, low humidity leaves contain only ~1% water Night: cooler, lower humidity leaves contain ~40% water Oryx feed on Diasperma primarily at night, relying on more succulent plants during day

Temperature Regulation -metabolic processes produce heat Evaporative Cooling -major mechanism of heat dissipation -very effective but requires water & convection -water absorbs heat as it evaporates (changes from liquid to vapor) Two major methods: 1. Sweating 2. Panting

Panting 2. heat & water both lost from evaporative surfaces of nose & mouth - rapid shallow breathing - promotes evaporative heat loss from upper respiratory tract 1. exhaled air is hotter & moister than outside air 3. some water conserved as it condenses: moist, hot outgoing air contacts cooler, drier incoming air especially in nasal cavities

Sweating vs. Panting -panting animal provides own air flow over the moist surface of upper respiratory tract -sweating animal relies on convection -can control degree of evaporative cooling -some metabolic costs

Sweating & Panting Downsides -lose water with both -sweating, also lose electrolytes -panting uses muscular activity and thus generates some heat Upsides -both promote evaporative heat loss -panting combined with countercurrent exchange can help keep brain cool

Very important to keep brain cool special counter-current system to cool brain -lies between nasal sinus & brain -cool venous blood from nasals runs along warm arterial blood entering from body via the carotid artery carotid rete

hot cool -after passing through the carotid rete arterial blood is much cooler blood from heart is relatively hot heat dissipated from arteries before it makes it to the brain

-Also important in preventing overheating during exertion

Saliva spreading: -many rodents rely heavily on this -most effective in dealing with short-term heat stress less effective than sweating because hair must be saturated

Most animals don’t face desert heat head on use shelters (burrows) & modify activity to avoid hottest periods

Estivation (or aestivation) -period of dormancy in reaction to excessive heat -animal more lethargic than torpid pocket mouse (Chaetodipus spp.) -decrease body temp -reduce metabolic rate -also a reaction to low food supply

Antelope ground squirrel -only spends minutes above ground at at a time during heat of day -poor thermal inertia; heats up quick (hyperthermic) -uses tail as a parasol for shade -returns to cool burrow to lower body T

-large body size = high thermal inertia (heats up and cools down slowly) -can let body get hyperthermic during day and cool down at night -effective even when water is limited (but body Temp. fluctuates more)

Temperature of sand in Namib Desert open areaunder vegetation -Temperature fluctuates much less just 20cm below surface of sand

Golden mole Body temperature of moles as they were plucked from sand at varying depths

Cetaceans are large and have lots of insulation Heat buildup can be a problem during periods of high exertion -warm blood sent to the spermateceti organ -cold water enters blowhole and into nasal passages -heat from blood dissipated to cold seawater and ejected out blowhole sperm whale

Summary - Overheating and water loss both problems for mammals in hot environs. - Many adaptations, but most mammals simply avoid the hottest temps - Evaporative cooling major mechanism of releasing excess heat -limited by water loss - Free water usually not available; need to get it from food - Exertion can also cause similar overheating problems