Thermoregulation

Temperature Effects on Animals

1. The Effects of Temperature

Distribution of Animals

  • The location of an animal is influenced by the temperature of its habitat.

  • Example: Ophiodon elongates (lingcod) is typically found in water at a temperature of 12°C.

Daily Patterns

  • Animals may find their preferred temperature ranges at specific times of the day, affecting their activity levels.

Active and Inactive Periods

  • Temperature influences when animals are active or inactive.

Migration

  • Animals migrate seasonally based on temperature changes, in addition to other environmental cues.

  • ### Species Variation

    • Species differ in their ability to survive various temperature ranges.

    • Important to remember that the viable temperature range for many species spans from -2°C to 50°C. Within this range, temperature significantly impacts physiological processes.

2. Q10 Coefficient

  • Definition: The Q10 coefficient measures the change in the rate of a physiological function (e.g., metabolic rate) resulting from a 10°C increase or decrease in temperature.

  • Formula:
    Q10=MR(t+10)MRtQ10 = \frac{MR(t+10)}{MRt}

  • The value of Q10 often ranges from 2 to 3, indicating how sensitive metabolic processes are to temperature changes (Eckert 17-2).

3. Physiological Implications of Temperature

  • Increased Temperature: Leads to:

    • Enhanced rates of chemical reactions.

    • Increased metabolism.

4. Body Temperature Strategies

Poikilotherms

  • Organisms that have variable body temperatures that change with environmental temperatures.

Homeotherms

  • Organisms that maintain a relatively constant body temperature, regardless of environmental conditions.

  • most mammals and birds

Endotherms

  • Animals that regulate their body temperature through metabolic heat generation, allowing them to maintain a constant internal temperature.

  • ### Ectotherms

    • Animals that primarily rely on environmental temperatures for regulating their body temperature through behavioral adaptations.

5. Thermal Budget of Endotherms and Ectotherms (Eckert)

  • Inputs:

    • Absorption of Solar Radiation: Solar energy received by the surface of the animal.

    • Absorption of Infrared Radiation: Thermal radiation from surroundings.

    • Convection: Heat exchange with surrounding air or water.

    • Conduction: Heat transfer between the animal and objects it contacts.

    • Metabolism: Heat produced through biological processes.

  • Outputs:

    • Emitted Infrared Radiation: Heat emitted as thermal radiation.

    • Convection: Heat loss through surrounding fluid.

    • Conduction: Heat transferred to substrates in contact.

    • Storage: The capacity of an animal to retain heat.

6. Temperature Dynamics

  • Heat Gain (or Loss) Calculation:
    Heat Gain (or Loss)=radiation absorbed+metabolic heat production+infrared radiation emitted/received+convection exchanges+condensation/evaporation+conduction\text{Heat Gain (or Loss)} = \text{radiation absorbed} + \text{metabolic heat production} + \text{infrared radiation emitted/received} + \text{convection exchanges} + \text{condensation/evaporation} + \text{conduction}

7. Examples of Solar Radiation Impact

  • Factors Affecting Solar Radiation Absorption:

    • Location: Whether in shade or sunlight.

    • Posture: Body positioning can alter exposure to solar radiation.

    • Color: Melanin presence in melanophores influences absorption efficiency.

8. Infrared Radiation Considerations

  • Surfaces of animals have distinct thermal properties:

    • Matte Surfaces: Absorb and emit infrared radiation well.

    • Smooth Surfaces: Absorb and emit infrared radiation poorly.

9. Convection and Body Size

  • Temperature Influence through Convection: Fluid movements aid in heat dissipation (e.g., lizards climbing bushes to escape midday heat).

  • Body Size Implications:

    • Small body size leads to quicker temperature changes.

    • Larger body size is less sensitive to convection effects.

10. Metabolic Heat Production

  • Chemical energy transformed during metabolism is typically lost as heat, impacting overall thermal balance (Pough et al., 2001).

  • Notably, larger species can display some endothermic characteristics due to:

    • Their ratio of surface area to volume, such as seen in the leatherback turtle (Dermochelys coriacea).

11. Temperature Regulation Mechanisms

Ectothermic Strategies

  • Evaporation and Condensation: Some species exhibit behaviors like panting when overheated.

  • Conduction: Aquatic ectotherms maintain roughly the same temperature as surrounding water.

  • Heat Storage: Large ectotherms retain heat, impacting their thermal regulation capabilities.

Aquatic Ectotherms

  • Highly conductive aquatic environments have:

    • A low level of radiation from water.

    • Limited capability for heat loss through evaporation.

Amphibians

  • Tadpoles share similar thermal regulation strategies as fish.

  • Terrestrial amphibians can increase body temperature through selective microhabitat use.

12. Thermoregulation in Ectotherms

  • Temperature Set Point: Often a narrow range maintained by sensors that can change with seasonal variations (e.g., gravidity, infection).

  • Thermoregulatory Mechanisms: Controlled by the hypothalamus through sensory input, integration, and effector responses.

Variables to Consider in Thermoregulation

  • Behavioral Adaptations:

    • Microhabitat selection.

    • Timing of activity (e.g., diurnal versus nocturnal).

    • Adjustments in posture to optimize heat exchange:

    1. Prostrate to maximize conduction and minimize convection.

    2. Elevation of the front body to aid in heat loss.

    3. Elevation from substrates can aid in cooling down.

Integration of Integuments

  • Utilized to modify heating and cooling through changes in skin color.

  • Cardiovascular Adjustments:

    • Peripheral dilation increases heat loss.

    • Peripheral constriction reduces cooling through blood flow regulation.

Evaporation as Heat Transfer

  • Panting: Represents a significant evaporative cooling mechanism, facilitating the loss of water during respiration.

13. Temperature Tolerance in Ectotherms

  • Lethal Temperatures: Defines the range within which ectotherms can survive; death or loss of function occurs beyond this range.

  • Pilot Experiments: To determine lethal temperatures (LT50) across various species have shown:

    • Upper tolerance examples:

    • Desert pupfish (Cyprinodon macularius): Survives in the range of 40-41°C with an LT50 of 43°C.

    • Goldfish: LT50 of 37°C.

    • Antarctic fish (Trematomus): LT50 of 6°C, adapted to live at -1.0°C.

Heat Shock Proteins

  • Molecules that act as chaperones, preventing proteins that have unfolded from aggregating and promoting their proper folding into a functional three-dimensional state.

14. Lower Temperature Tolerance

  • Freezing: Leads to ice crystal formation, altering cellular osmolality and causing physical destruction.

  • Freeze Resistance: Mechanisms to avoid ice crystallization (e.g., species like Sceloporus jarrovii and Chrysemys picta).

  • Freeze Tolerance: Some species like Rana sylvatica use glucose or glycerol as natural antifreeze agents within their cells (Pough et al., 2001).

15. Advantages and Disadvantages of Ectothermy

  • Advantages: Ectotherms spend relatively small amounts of metabolic energy on thermoregulation.

  • Disadvantages: Potential biochemical and physiological limitations, impacting energetic efficiency and survival related to thermal regulation.

16. Endothermic Regulation

  • Thermoregulatory Mechanisms in Endotherms:

    • The concept of a thermoneutral zone—where metabolic output is minimized while maintaining a stable temperature.

    • Adaptations to Cold:

    • Strategies include reduced heat loss through insulation and enhanced metabolic efficiency.

    • Torpor: A state of decreased physiological activity.

    • Adaptations to Heat:

    • Size increase as an adaptation for heat regulation.

    • Behavioral changes (e.g., curling into a ball to reduce surface area).

    • Huddling: to decrease heat loss.

17. Mechanisms to Increase Heat Production in Endotherms

  • Skeletal Muscle Contraction: Shivering is a rapid involuntary muscle contraction method for heat production.

  • Non-shivering Thermogenesis: Involves the metabolic activity of brown fat to generate heat.

  • Activity Levels: Increased activity can also raise body temperature.

  • Specific Dynamic Action (SDA): The energy expenditure associated with metabolizing food, contributes to heat production.

  • Solar Radiation Absorption: Gains heat from sun exposure.

  • Counter-Current Heat Exchange: Utilizing fine vessels enables animals to retain body heat effectively.

18. Upper Temperature Regulation in Endotherms

  • Behavior: Adapting behaviors to minimize thermal stress.

  • Pelage Thickness: Variations in fur or body coverings assist in temperature regulation.

  • Strategies for Evaporation:

    • Sweating, Panting, Gular Fluttering: behaviors to facilitate evaporative cooling.

    • Salivary Spreading: A method of cooling through saliva application.