Warm
Turtle
in Cold Water...
Metabolic
Heat
Unlike most of its reptile relatives which are thermoconformers
and vary their body temperatures, leatherbacks can maintain a constant body
temperature over a broad range of ambient temperatures. Leatherbacks use several
different evolutionary and thermoregulatory adaptations to accomplish this
feat. Big body mass, insulation,
and counter current heat exchange allow leatherbacks
to contain metabolic heat generated by muscles and other tissue, keeping them
warm even in frigid waters.
Oxygen consumption of pectoralis muscle
from green and leatherback turtles. Error bars represent + or - 1 SE.(Penick
et, al., 1998)
Most
reptiles have to thermoregulate behaviorally by basking, hibernating, changing
their body posture, or hiding in the shade, just to name a few. By changing
their behavior to obtain desired body temperatures, reptiles demonstrate that
their physiological functions are thermally dependent. This simply means that
if a reptile is not in the right temperature range then its physiological functions,
such as digestion and crawling speed are not operating at optimal or peak levels.
Because, metabolic rates of animal tissues typically decrease with decreasing
temperature, most animals (especially reptiles) cannot function in cold environments.
When an animal's temperature and metabolic rate drop to the point where it loses
the ability to carry out normal functions, it is said to be 'cold stunned'.
For example, outside of tropical or sub-tropical waters, green sea turtles are
highly susceptible to cold stunning and they lose the ability to swim and dive
(Penick et al., 1998). Therefore, green sea turtles and most other reptiles
are highly dependent on environmental conditions to regulate physiological functions.
Although
most reptiles lose the ability to function optimally outside of tropical or
sub-tropical temperatures, leatherbacks have proven that their muscle tissue
metabolism is thermally independent of their environment or remains stable over
a broad range of ambient temperatures. This metabolic adaptation is one of the
biggest factors that allow leatherbacks to journey into cold artic waters. In
one study, the metabolic rates of leatherback pectoralis muscles were completely
insensitive from 5 to 35 degress Celcius (Penick et al., 1998). The ability
to uncouple muscle function from its surroundings using their big bodies and
counter current heat exhcangers has played a key role in enabling the leatherback
to
successfully
disperse to different thermal niches all around the planet. In almost any ambient
temperature, leatherbacks' muscles function at an optimal metabolic level, so
they have the ability to be active when other turtles cannot. Another important
source of metabolic heat for leatherbakcs is their liver. They have a very large
liver and as it breaks down nutrients it also generates heat (Euro
Turtle). Through the use of insulation, counter current heat exchangers,
and big body mass, leatherbacks are able to contain most of the metabolic heat
generated by their liver and muscles, allowing them to stay warm, even in cold
water.
main homepage. 