Mammalian structure and function: endothermy Flashcards
Describe Mammalia
- group of animals with backbones, and bodies insulated by hair
- nurse their infants with milk and share a unique jaw articulation
Give the characteristics of modern mammals
- single bone in mandible
- two occipital condyles
- long bones with epiphyses (determinant growth)
- four-chambered heart (with left aortic arch)
- dentition (more on next lecture)
- middle ear with three ossicles
- epidermis with hair
- viviparous (except monotremes)
- mammary glands
- endothermic (high metabolic rate)
Describe the smallest mammal
- ~2g Kitti’s hog-nosed bat
- Craseonycteris thonglongyai
- bumblebee bat (smallest mammal)
Describe the largest mammal
- blue whale
- Balaenoptera musculus
- 100 million times biggest
Describe long ranging mammals
- African wild dog
- Lycaon pictus
- roam a home range of 2,500km2
Describe sedentary mammals
- naked molerats
- Heterocephalus glaber
- never leave their burrow
- up to 28 pups in one litter
Describe slow developing mammals
- 22 months to gestate a calf
- live up to 70 years
Describe short-lived developing mammals
- male of the brown antechinus (Antechinus stuartii)
- never sees a second season and dies before the first and only litter it has fathered
Subclass Protheria
- Monotremes
- Order Monotremata
- 5 species in 3 genera and 2 families
- Egg layers
Describe Subclass Theria
- live bearers
Describe endothermy
- cold environments or be active at night
- high BMR (7-10 times higher than ectotherms)
- high food requirements
- high internal body temperature (28-42 °C)
- constant internal body temperature (± 2 °C)
- high aerobic metabolic scope (5-10 times higher)
Describe BMR
metabolic activity required for minimal resting lifestyle with no spontaneous activity, digestion and no stress (physical, thermal or psychological).
Heat exchanges with the environment IN
- direct solar radiation
- thermal radiation from atmosphere and socks
- reflected light
Heat exchanges of endoderms OUT
- thermal radiation to ground and sky
- evaporation
- conduction
Describe winter survival mechanisms
– avoidance (energy conservation)
- body size
- insulation
- appendages
- colouration
- migration (marine mammals)
- microclimate modification (communal nesting, elaborate nests)
- food hoarding
- reduction in activity
- reduction in body mass
- dormancy
Describe endotherm body size
- allometry
- Bergmann’s rule
allometry
as the size of an animal increases, volume and mass change more rapidly than area
Bergmann’s rule (1987)
“on the whole…larger species further north and the smaller ones further south” (1987)
Describe endotherm insulation
- insulating values of pelts are proportion to length of hair
Describe the Arctic fox
- winter coat
- lower critical Tb of -40 °C
- Ta of -70°C
Describe blubber
- insulation in marine mammals
- fat + collagene
- up to 40% of body mass
Describe behavioural thermoregulation of marine mammals
- saving hind flippers (sweat glands)
- panting
- reduced activity
Describe regional heterothermy
- countercurrent heat exchange
- circulation in limb of a mammal
Describe thermoregulation in caribou
- regulation of external body T
- meshwork of veins and arteries keep T of limbs near that of environment so heat is not lost
Allen’s rule (1877)
- “…mammals (and birds) living in cold climates have shorter appendages than do close relatives in warmer climates”.
- e.g. foxes and hares
Describe microclimate modification
- winter survival mechanisms
- taiga vole: burrows, food cache chambers, nesting chambers
Describe Gloger’s rule (1833)
“races in warm and humid areas are more heavily pigmented than those in cool and dry areas”
Describe colouration in
Springbok
- colouration and differential heating
- white winter coat in Arctic mammals
Describe the reduction of BMR for endotherms
- reduction in activity (e.g. shrews)
- Dehnel’s phenomenon
- dormancy
- torpour
- hibernation
Dehnel’s phenomenon
- reduction in body mass
- general overwinter mass decline (e.g. voles and shrews)
Describe the dormancy
- temporal abandonment of euthermia
- reduced metabolic rate & lowering of body T
- exhibited in seven orders: marsupials, insectivores, elephant shrews, bats, primates, carnivores
Torpour
- body T, heart rate & breathing are lowered
- tolerable body T range 10-20 °C
- daily torpor – response to an immediate energy emergency
Describe winter torpour
- profound dormancy
List some mammals with particularly low BMRs
- Marsupials, especially koalas
- Tenrecs
- Sloths
- Echidnas
Describe hibernation
- animal remains at Tb of 2-5°C for weeks in winter
- hedgehogs, ground squirrels, marmots (largest to undergo hypothermia)
Describe adaptations to heat
- majority nocturnal activity
- avoid exposure to high temperatures
- burrow during the day/patches of shades
List some heat-adapted mammals
- Fennec
- Heath shield of Cape ground squirrel
Describe thermoregulation in Dipodomys
- burrowing during day
- respiratory moisture
- metabolic water derived from dry seeds
- faeces dehydrated prior to defecation
- urine concentration by countercurrent exchange in extra long loop of Henle
Describe the relationship between evaporation and body mass
- increases rapidly
- assumes heat load is proportional to body surface
Describe cranial thermoregulation
- anatomic arrangement
promotes cooling of the brain - arterial and (cool) venous vessels flow in intimate juxtaposition in the cavernous sinus
- evaporation in nasal passages
Describe resistance endothermy
- increase in thermogenic capacity (BMR)
- non-shivering thermogenesis
- shivering
Endothermy evolution
- Nocturnalisation
▪ Aerobic capacity (Bennet and Ruben, 1979): higher metabolism
▪BUT larger need of food
▪ and increased metabolism on ectotherms - heat wasted if no insulation
