Vertebrate Zoology Exam 2 - Endothermy/Ectothermy

Homeothermy

Stable body temperature (doesn’t fluctuate in a range of 2°C)

Heterothermy

Variable body temperature (DOES fluctuate in more than a range of 2°C)

Endothermy

Internal (metabolic) heat production

Ectothermy

Primary source of heat is from outside of the body (external heat)

Solar radiation

Solar energy resulting in heat gain

Infrared (thermal) Radiation

Heat loss or gain from proximity to other objects

Convection

Transfer of heat between animal and fluid (such as air)

Conduction

Heat exchange that occurs from objects being in contact

Evaporation

Heat loss (transfer of heat from animal to environment through evaporation of water)

Metabolism (Metabolic Heat Production)

Main source for endotherms

Trivial in ectotherms

Activity Temperature

Range within which physiological processes and whole-animal performance reach their maxima

Endothermy Costs/Benefits

Benefits

• Effective when solar radiation is insufficient or unavailable (cold, night)

Costs

• Energetically expensive (high metabolic rate)

Why is metabolism inefficient?

A small portion of energy is captured; the majority is released to the environment as heat

How do endotherms regulate their body temperatures?

Rate of metabolic heat production = rate of heat loss to environment across body surface

Normothermia

Normal body temperature

Thermoneutral Zone

Endotherms

Environmental temperature range where endotherm maintains stable body temperature by adjusting its insulation and without changing its metabolic rate

• Bound by lower and upper critical temperatures

Whole-body metabolism

Sum of the heat production across all of an organism’s different tissues and organs

• Measured by weight-specific resting metabolic rates (kilojoules/kilogram/day, kJ/kg/day)

What are the most metabolically active tissues?

Heart and kidneys

Where is most of the resting metabolic heat production of an endotherm derived from?

Heart and kidneys

• Muscular activity typically not significant at rest

Shivering

Birds and mammals

Uncoordinated contraction of postural muscle fibers

• Thermogenesis

Non-shivering thermogenesis

Oxidative phosphorylation increased by proton leak back into matrix without passing through ATP synthase, resulting in heat release

How does insulation increase an organism’s temperature?

Increases thickness of layer of trapped air

• Can also be minimized by exposing thinly insulated parts of body (Pogi, my dog, lying on his back)

Types of Evaporative Cooling

• Panting (breathing rapid + shallow)

• Gular fluttering (birds rapidly flutter throat to evaporate water for thermoregulation)

• Sweat glands (SOME mammals, most lack sweat glands)

What is the downside of sweating, panting, and gular fluttering?

Sweating - Cools only surface, not internally

Panting & gular fluttering - cools internal tissues, but requires muscular activity

Endothermal Ectotherm Examples

S. merianae, a Tegu, can maintain higher body temperatures in burrows (pictured)

Python bivittatus, Burmese Python females can maintain high body temperature when incubating

Torpor

Controlled reduction in body temperature to a new set point

Why do endotherms induce a state of torpor?

The energy cost of maintaining homeothermy may be prohibitive

Hibernation

Deep torpor, comatose condition

What type of animals benefit the most from deep torpor?

Small animals (almost entirely small mammals)

• Weigh-specific energy cost higher for small animal than large one

• Small animals experience more rapid heat loss than large ones

Hyperthermia

Temporarily allowing the body temperature to rise above a species’ normal set point

• For water conservation

Large heterothermal mammals

• Mobile and can travel long distances to find foor or water

• Low surface/volume ratios

• High insulation (low heat absorption)

• Large body weight = high thermal inertia, can absorb a large amount of heat before body temp. is too high

Endothermy & Body Size

• Endothermy has a high energetic cost

• More costly at smaller body sizes

• Energy sets a lower limit of endotherm body size

How do endotherms and ectotherms differ with the energy they produce?

Endotherms: >90% of energy maintaining body temp

Ectotherms: ~50% to production of biomass (new tissue), the other 50% to maintenace