Comparative Anatomy and Physiology of Animals
Lecture 14 Adaptations to cold environments 02/12/20
Cold environments
- Low temperatures are common at high latitudes, high altitudes, and is also seasonal in
temperate locations.
- Cold does not always mean problematic physiological problems for all species.
- Need to understand “normal” temperatures for activity are not the same for all species.
Responses of fishes to potential freezing
- Low temperature does not necessarily reduce activity in acclimated fishes.
- Freezing is an issue because of ice formation in the tissues, caused by contact with ice
crystals (nucleation).
- Marine teleosts- body fluids freezing point is -0. 8 oC.
- Polar oceans temperature is -1.8oC.
- Produce antifreeze proteins in liver and epidermis that absorb ice crystals to prevent them
from growing.
- Lowers freezing point of blood and minimise the risk of ice nucleation.
- Also, accumulation of glycerol in the blood.
Response of amphibians and reptiles to cold conditions
- Winter dormancy “hibernation”.
- Migration is rarely an option.
- Aquatic- bottom of water bodies that often freeze over at surface.
- Ice prevents air breathing so need to use skin or gills- aerobic activity causes hypoxia.
- Metabolic depression due to Q10 effect and hypoxia – lower rates of energy reserves.
Responses of reptiles to cold conditions
- Painted turtles (Chrysemys picta) remains in the nest to overwinter.
- No antifreeze in their body, but turtles remove nucleating agents from their bodily fluids and
organs- bodily fluids remain in a supercooled, liquid state.
- Integument is barrier to the penetration of ice into the body from the frozen soil.
- Increased reliance on anaerobic metabolism, circulatory system caused to shut down by
declining temperature.
- Alterations in acid/base status resulting from the accumulation of lactic acid may limit
survival by supercooled turtles.
Cold tolerance in birds
- Smaller birds have higher metabolic rates, higher SA:V ratio, and less insulation.
- Low temperatures lead to increased metabolic rate to increase heat production and
maintain high body temperatures.
- Bergman’s rule (1847): colder it gets, larger the body size, so high latitude species should be
bigger.
- Two main responses to cold temperatures: migration to avoid exposure or stay put and
respond to cold temperatures.
- In order to ensure high temperatures are maintained, birds have to adjust their basal
metabolic rate to counter increased loss of heat at cold temperatures.
Adjustments of BMR
- Shivering: involuntary isotonic trembling of skeletal muscle that generates heat. Commences
below critical low threshold – BMR cannot keep T b stable. Muscles have to fatigue-resistant
and most muscle fibres are not involved. Can increase BMR 5-fold (other physical activity =
Lecture 14 Adaptations to cold environments 02/12/20
Cold environments
- Low temperatures are common at high latitudes, high altitudes, and is also seasonal in
temperate locations.
- Cold does not always mean problematic physiological problems for all species.
- Need to understand “normal” temperatures for activity are not the same for all species.
Responses of fishes to potential freezing
- Low temperature does not necessarily reduce activity in acclimated fishes.
- Freezing is an issue because of ice formation in the tissues, caused by contact with ice
crystals (nucleation).
- Marine teleosts- body fluids freezing point is -0. 8 oC.
- Polar oceans temperature is -1.8oC.
- Produce antifreeze proteins in liver and epidermis that absorb ice crystals to prevent them
from growing.
- Lowers freezing point of blood and minimise the risk of ice nucleation.
- Also, accumulation of glycerol in the blood.
Response of amphibians and reptiles to cold conditions
- Winter dormancy “hibernation”.
- Migration is rarely an option.
- Aquatic- bottom of water bodies that often freeze over at surface.
- Ice prevents air breathing so need to use skin or gills- aerobic activity causes hypoxia.
- Metabolic depression due to Q10 effect and hypoxia – lower rates of energy reserves.
Responses of reptiles to cold conditions
- Painted turtles (Chrysemys picta) remains in the nest to overwinter.
- No antifreeze in their body, but turtles remove nucleating agents from their bodily fluids and
organs- bodily fluids remain in a supercooled, liquid state.
- Integument is barrier to the penetration of ice into the body from the frozen soil.
- Increased reliance on anaerobic metabolism, circulatory system caused to shut down by
declining temperature.
- Alterations in acid/base status resulting from the accumulation of lactic acid may limit
survival by supercooled turtles.
Cold tolerance in birds
- Smaller birds have higher metabolic rates, higher SA:V ratio, and less insulation.
- Low temperatures lead to increased metabolic rate to increase heat production and
maintain high body temperatures.
- Bergman’s rule (1847): colder it gets, larger the body size, so high latitude species should be
bigger.
- Two main responses to cold temperatures: migration to avoid exposure or stay put and
respond to cold temperatures.
- In order to ensure high temperatures are maintained, birds have to adjust their basal
metabolic rate to counter increased loss of heat at cold temperatures.
Adjustments of BMR
- Shivering: involuntary isotonic trembling of skeletal muscle that generates heat. Commences
below critical low threshold – BMR cannot keep T b stable. Muscles have to fatigue-resistant
and most muscle fibres are not involved. Can increase BMR 5-fold (other physical activity =
