Try to hold your breath for more than 2-3 minutes, and those around you will have to call the ambulance. But the sperm whale can dive for more than one hour to depths greater than 1,200 meters (roughly 4,000 feet), with average dives of 45 minutes, to depths of 600-1,000 meters (1,968 to 3,280 feet). Elephant seals can spend up to two hours in depths over 1,500 meters (nearly 5,000 feet), but average dives last only 25-30 minutes, to depths of about 500 meters (1,640 feet).
Cuvier's beaked whales dive to maximum depths of nearly 1,900 meters (about 6,230 feet) with a maximum duration of 85 minutes. The average foraging dive for Cuvier's beaked whale is to a depth of 1,070 meters (about 3,500 feet) with a duration of 58 minutes. And all these seals and whales do it without passing out because of the lack of oxygen. A new research, published in the journal "Proceedings of the Royal Society B", shows that the secret is found in the amounts of special oxygen-carrying proteins encountered in their brains.
It has been thought for long that hypoxia (low oxygen) tolerance in sea mammals was due to their adaptations to increase oxygen transport to the brain. But, many researches showed that the oxygen amounts in their blood vessels dropped within minutes of diving.
"The kinds of levels we were seeing in arterial blood would have caused us to black out under
water", said lead author Terrie Williams, professor of ecology and evolutionary biology at the University of California, Santa Cruz.
The team investigated two newly found proteins, called neuroglobin and cytoglobin. They resemble hemoglobin, blood's iron-containing protein that transports oxygen, but these globins are encountered only in the brain. The researchers investigated levels of hemoglobin and brain globins in 16 mammal species, from land mammals (like bobcat and mountain lion) to shallow swimmers (like the bottlenose dolphin and California sea lion) and deep divers (like the pilot whale and Risso's dolphin).
Generally, the brains of sea mammals had higher amounts of hemoglobin and brain globins than those of terrestrial mammals, pointing that these proteins were involved in diving. The shallow-swimming and highly energetic bottle-nose dolphins, sea lions and sea otters presented larger levels of brain globins than the deep-diving whales.
"The agile swimmers need to shuttle oxygen quickly to the brain and so they rely on the brain globins rather than the hemoglobin. The more hemoglobin in the blood, the more viscous the blood becomes, making transport to the brain slower", said Williams.
But the researchers were surprised to find that the bobcat, opposite to dog-related species like foxes and coyotes, presented high levels of the brain globins in their tissues.
"Maybe it's not just breath-holding that stimulates these globins, but high levels of activity, such as sprinting", said Williams.
The discovery could explain strokes and aging in humans; by increasing globin synthesis in humans, the brain could be protected from negative effects of disease and aging.
"[The diving mammals] might be the group to look toward, because evolution and selective pressures would push them toward better protection", said Williams.
It has recently been proved that bowhead whales could live up to 200 years and more.
"What if you could do something that would keep your brain active for twice as long?" asked Williams.
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