Evolution: aquatic mammal low oxygen adaptations (Evolution)

by David Turell , Thursday, December 03, 2020, 22:00 (1233 days ago) @ David Turell

Extraordinary changes were required and this is what is found:

https://phys.org/news/2020-12-marine-mammals-oxygen-perspective-covid-.html

"'Diving marine mammals experience a lifetime of rapid physiological transitions between normal oxygenation and hypoxia [low oxygen levels]," Williams said. "They've got ways to protect themselves and allow their organs to keep functioning while holding their breath for hours at a time, but there's a whole suite of biological adaptations that had to happen for them to be able to do that."

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"The heart and brain are especially sensitive to oxygen deprivation, and marine mammals have multiple mechanisms to protect these and other critical organs. In the first place, marine mammals have much higher oxygen carrying capacity than humans due to their greater blood volume and hemoglobin concentrations. In addition, some marine mammals contract their spleen during dives to release a store of oxygen-rich blood cells into the circulation. To avoid blood clots resulting from such high concentrations of red blood cells, many species lack a key clotting factor found in other mammals.

"Other adaptations include greatly increased concentrations of oxygen-carrying proteins such as myoglobin in heart and skeletal muscles and neuroglobin and cytoglobin in the brain. In addition, numerous safety factors and biochemical buffers enable even the most oxygen-dependent tissues in marine mammals to withstand not only low oxygen but also the subsequent reperfusion of tissues with oxygenated blood. In humans, reperfusion after a heart attack or stroke often leads to additional tissue damage."

Comment: These are intense physiological and phenotypical alterations. It always raises the observation, why if survival as a mammal is so complex why did mammals enter an aquatic life? Unless there is great stress for survival it is a very difficult path to follow. Migration to a better spot is more sensible and practical. Note human divers also can develop the ability to contract the spleen after persistent deep diving. That and prolonged control of the respiratory center is all humans can accomplish by practice.