Mammalian structure and function: endothermy

Question 1

Describe Mammalia

Answer 1

• group of animals with backbones, and bodies insulated by hair
• nurse their infants with milk and share a unique jaw articulation

Question 2

Give the characteristics of modern mammals

Answer 2

• 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)

Question 3

Describe the smallest mammal

Answer 3

• ~2g Kitti’s hog-nosed bat
• Craseonycteris thonglongyai
• bumblebee bat (smallest mammal)

Question 4

Describe the largest mammal

Answer 4

• blue whale
• Balaenoptera musculus
• 100 million times biggest

Question 5

Describe long ranging mammals

Answer 5

• African wild dog
• Lycaon pictus
• roam a home range of 2,500km2

Question 6

Describe sedentary mammals

Answer 6

• naked molerats
• Heterocephalus glaber
• never leave their burrow
• up to 28 pups in one litter

Question 7

Describe slow developing mammals

Answer 7

• 22 months to gestate a calf
• live up to 70 years

Question 8

Describe short-lived developing mammals

Answer 8

• male of the brown antechinus (Antechinus stuartii)
• never sees a second season and dies before the first and only litter it has fathered

Question 9

Subclass Protheria

Answer 9

• Monotremes
• Order Monotremata
• 5 species in 3 genera and 2 families
• Egg layers

Question 10

Describe Subclass Theria

Answer 10

• live bearers

Question 11

Describe endothermy

Answer 11

• 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)

Question 12

Describe BMR

Answer 12

metabolic activity required for minimal resting lifestyle with no spontaneous activity, digestion and no stress (physical, thermal or psychological).

Question 13

Heat exchanges with the environment IN

Answer 13

• direct solar radiation
• thermal radiation from atmosphere and socks
• reflected light

Question 14

Heat exchanges of endoderms OUT

Answer 14

• thermal radiation to ground and sky
• evaporation
• conduction

Question 15

Describe winter survival mechanisms

Answer 15

– 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

Question 16

Describe endotherm body size

Answer 16

• allometry
• Bergmann’s rule

Question 17

allometry

Answer 17

as the size of an animal increases, volume and mass change more rapidly than area

Question 18

Bergmann’s rule (1987)

Answer 18

“on the whole…larger species further north and the smaller ones further south” (1987)

Question 19

Describe endotherm insulation

Answer 19

• insulating values of pelts are proportion to length of hair

Question 20

Describe the Arctic fox

Answer 20

• winter coat
• lower critical Tb of -40 °C
• Ta of -70°C

Question 21

Describe blubber

Answer 21

• insulation in marine mammals
• fat + collagene
• up to 40% of body mass

Question 22

Describe behavioural thermoregulation of marine mammals

Answer 22

• saving hind flippers (sweat glands)
• panting
• reduced activity

Question 23

Describe regional heterothermy

Answer 23

• countercurrent heat exchange
• circulation in limb of a mammal

Question 24

Describe thermoregulation in caribou

Answer 24

• regulation of external body T
• meshwork of veins and arteries keep T of limbs near that of environment so heat is not lost

Question 25

Allen’s rule (1877)

Answer 25

- “...mammals (and birds) living in cold climates have shorter appendages than do close relatives in warmer climates”. - e.g. foxes and hares

Question 26

Describe microclimate modification

Answer 26

- winter survival mechanisms - taiga vole: burrows, food cache chambers, nesting chambers

Question 27

Describe Gloger’s rule (1833)

Answer 27

“races in warm and humid areas are more heavily pigmented than those in cool and dry areas”

Question 28

Describe colouration in Springbok

Answer 28

- colouration and differential heating - white winter coat in Arctic mammals

Question 29

Describe the reduction of BMR for endotherms

Answer 29

- reduction in activity (e.g. shrews) - Dehnel’s phenomenon - dormancy - torpour - hibernation

Question 30

Dehnel's phenomenon

Answer 30

- reduction in body mass - general overwinter mass decline (e.g. voles and shrews)

Question 31

Describe the dormancy

Answer 31

- temporal abandonment of euthermia - reduced metabolic rate & lowering of body T - exhibited in seven orders: marsupials, insectivores, elephant shrews, bats, primates, carnivores

Question 32

Torpour

Answer 32

- body T, heart rate & breathing are lowered - tolerable body T range 10-20 °C - daily torpor – response to an immediate energy emergency

Question 33

Describe winter torpour

Answer 33

- profound dormancy

Question 34

List some mammals with particularly low BMRs

Answer 34

- Marsupials, especially koalas - Tenrecs - Sloths - Echidnas

Question 35

Describe hibernation

Answer 35

- animal remains at Tb of 2-5°C for weeks in winter - hedgehogs, ground squirrels, marmots (largest to undergo hypothermia)

Question 36

Describe adaptations to heat

Answer 36

- majority nocturnal activity - avoid exposure to high temperatures - burrow during the day/patches of shades

Question 37

List some heat-adapted mammals

Answer 37

- Fennec - Heath shield of Cape ground squirrel

Question 38

Describe thermoregulation in Dipodomys

Answer 38

- 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

Question 39

Describe the relationship between evaporation and body mass

Answer 39

- increases rapidly - assumes heat load is proportional to body surface

Question 40

Describe cranial thermoregulation

Answer 40

- anatomic arrangement promotes cooling of the brain - arterial and (cool) venous vessels flow in intimate juxtaposition in the cavernous sinus - evaporation in nasal passages

Question 41

Describe resistance endothermy

Answer 41

- increase in thermogenic capacity (BMR) - non-shivering thermogenesis - shivering

Question 42

Endothermy evolution

Answer 42

- Nocturnalisation ▪ Aerobic capacity (Bennet and Ruben, 1979): higher metabolism ▪BUT larger need of food ▪ and increased metabolism on ectotherms - heat wasted if no insulation