Dive Physiology: Aquaporin duplication in human genome

[wet]

[I'd appreciate any comments on whether AQP7 may have duplicated in the human genome (selected for in our ancestors) because of daily diving (breath hold O2 conservation) giving a survival advantage.]

An analysis of DNA from 10 primate species reveals that, compared with the genome of chimpanzees and gorillas, our genome includes many more duplicates of a gene called aquaporin 7 (AQP7), which transports water and sugary compounds into cells. Humans appear to have five copies of this gene, whereas chimps have just two, and other primates carry only one copy.

Genetic boost

Humans are believed to possess anywhere from 20,000 to 25,000 different genes. But in some cases, we carry multiple copies of the same gene. And the more duplicates of a gene that exist within a cell, the more protein from the gene that gets produced, according to James Sikela at the University of Colorado Health Sciences Center in Aurora, Colorado, US.

In some cases, though, having an extra copy of a gene can translate into a serious health problem. For example, a given cell normally has two copies of the gene for a brain protein called alpha-synuclein. But people born with a third copy of this gene are predisposed to developing Parkinson's disease.

Given the potential influence exerted by extra gene copies, Sikela and his colleagues wondered how humans might differ from other primate species in terms of the number of duplicates we carry. The team extracted DNA from blood samples taken from various primates including humans, along with chimpanzees, gorillas, baboons, lemurs and several others.

The researchers calculated how many copies of various genes each species carries with the help of DNA "micro-array" technology. If large quantities of the DNA from a given genome attached to certain parts of the micro-array chip, this indicated that it contained multiple copies of a specific gene.

After using this method to screen more than 20,000 genes, Sikela and his colleagues found 84 genes for which the copy number in the human genome differs from that of other primates.

Endurance boost

The AQP7 gene in particular caught their attention. The protein made by the gene functions as an important channel in the cell membrane. Specifically, the channel allows water and a sugary compound called glycerol to enter the cell, where they are used to produce energy. This has the potential to make a difference in long bouts of exercise, when the body needs to mobilise energy molecules from fat stores.

Duplicate genes help humans go the extra mile - being-human - 30 July 2007 - New Scientist

The source is New Scientist, the article focuses on endurance running on savannas, but I think diving played a larger part in the genetic selection for Aquaporin. Savanna chimps were not selected for aquaporin duplication any more than chimps which live in the deepest tropical rainforest, and savanna baboons were not selected for more aquaporin than rainforest monkeys, so IMO savanna living does not equal higher aquaporin duplication.

However, more efficient energy production while underwater is valuable to a breath-hold diver, for better endurance underwater (while surrounded by abundant water supplies) and extra fat stores is not detrimental to a diver (it insulates the body core aka "bioprene") but may be detrimental for a distance runner (See the Kenyan marathon runners and San Bushmen persistence hunters in the Kalahari desert, generally very skinny, almost no fat reserves, amidst scarce water resources.

DDeden

[wet]

"Breathing" through skin in mice and frogs: O2 detection

brief article note:

NewsBlog: The Scientist
Like frog, like mouse
Posted by Bob Grant
[Entry posted at 17th April 2008 05:06 PM GMT]
For the first time, scientists have identified in mammals an essential mechanism used by amphibians to adjust to low-oxygen environments.

According to a study published today (Apr 17) in the journal Cell, the skin of mice can sense oxygen levels in the air and helps the rodents cope with oxygen-poor conditions.

While science has long-known that epidermal gas...

[Adrian]

An analysis of DNA from 10 primate species reveals that, compared with the genome of chimpanzees and gorillas, our genome includes many more duplicates of a gene called aquaporin 7 (AQP7), which transports water and sugary compounds into cells

This is because, nature, in her infinite wisdom, knew humans would eventually be heavy drinkers and junk food eaters!

[octopus]

...but I think diving played a larger part in the genetic selection for Aquaporin.

There is one thing I cannot understand about Aquatic Ape hypothesis.
It claims that spending time in/around the water brought some evolutionary adaptations to humans. Assuming this is true, I wonder why our eyes did not adapt for underwater vision also. Eyes do adapt very quickly and it would take fairly modest change (evolutionary speaking) to see better underwater. Considering vision is the sense primates most rely on (our “top” sense) it seems it would have been under high evolutionary pressure (hence speeding it up).

[wet]

Originally Posted by octopus

There is one thing I cannot understand about Aquatic Ape hypothesis.
It claims that spending time in/around the water brought some evolutionary adaptations to humans. Assuming this is true, I wonder why our eyes did not adapt for underwater vision also. Eyes do adapt very quickly and it would take fairly modest change (evolutionary speaking) to see better underwater. Considering vision is the sense primates most rely on (our “top” sense) it seems it would have been under high evolutionary pressure (hence speeding it up).

CiteULike: Visual training improves underwater vision in children.

Since evolutionarily "recently" developing primitive boats and nets (whereby sitting/wading becoming more significant than diving) became employed for food foraging; diving and underwater vision have been under much less selection pressure. The high degree of nearsightedness/farsightedness in humans (not in plains dwelling animals) may indicate that childhood was once a period of visual plasticity.

Human ancestors did not become fully aquatic like whales, nor semi-aquatic specialists like sea lions (with their large round bulging eyes), but they maintained a general association with shore resources (waterside ambush of large game, mangrove oyster prying, sand clam digging, sea turtle egg digging) and off-shore food foraging (reef diving for molluscs, fish, crustaceans, sea urchins, kelp, aquatic plants), as well as inland foraging (fruits, nuts, flint for cutting tools), as omnivores; able to jog along beaches, wade in shallows, swim to nearby islets, dive more than a meter deep, backfloat while resting and nibbling, climb coconut palms and figs, climb rocky shore cliffs (caves, sea bird eggs, berry bushes), etc. Developing specialized aquatic vision like dolphins would have interfered with these mixed activities.

"Aquatic ape" does not mean fully adapted aquatics, but rather that our ancestors became the most water-associated of the known hominoids, while the others became more forest-associated or inland marsh-associated.
DDeden

[octopus]

Human ancestors did not become fully aquatic like whales, nor semi-aquatic specialists like sea lions (with their large round bulging eyes), but they maintained a general association with shore resources (waterside ambush of large game, mangrove oyster prying, sand clam digging, sea turtle egg digging) and off-shore food foraging (reef diving for molluscs, fish, crustaceans, sea urchins, kelp, aquatic plants), as well as inland foraging (fruits, nuts, flint for cutting tools), as omnivores; able to jog along beaches, wade in shallows, swim to nearby islets, dive more than a meter deep, backfloat while resting and nibbling, climb coconut palms and figs, climb rocky shore cliffs (caves, sea bird eggs, berry bushes), etc.

I do not think this is being point of argument between scientists. It is certainly not inconsistent with fossil evidence. Many characteristics (thermoregulation, descended larynx, breath control, fat, tears, sebaceous glands, body proportions) can be decently exaplained by the hypothesis.

...that childhood was once a period of visual plasticity.

Still is. This is when our neural nets form most of their connections for image processing. I think I could go with explanation like this. Humans do seem to have rather powerful processing aparatus, although image quality might not be the best, as our eye cannot focus underwater (problem at sensory end).

Thanks for the article - interesting stuff.
Gypsy Secret: Children of sea see clearly underwater: Science News Online, May 17, 2003

[wet]

Originally Posted by octopus

I do not think this is being point of argument between scientists. It is certainly not inconsistent with fossil evidence. Many characteristics (thermoregulation, descended larynx, breath control, fat, tears, sebaceous glands, body proportions) can be decently exaplained by the hypothesis.


Still is. This is when our neural nets form most of their connections for image processing. I think I could go with explanation like this. Humans do seem to have rather powerful processing aparatus, although image quality might not be the best, as our eye cannot focus underwater (problem at sensory end).

Thanks for the article - interesting stuff.
Gypsy Secret: Children of sea see clearly underwater: Science News Online, May 17, 2003

I forgot to note, todays great apes have much smaller eyeballs than humans and some prehistoric hominids; some (many?) neandertals and Homo erectus had large, more bulging forward (but beneath the protruding brow ridge) and slightly more lateral eyeballs. So it is possible that our ancestors 2ma - 100ka had proportionately larger eyes compared to brain size, and as the brain enlarged the eyes didn't keep increasing, due to more and more technological activities like fine tool crafting of spears, traps, baskets, dugout boats, etc. which were done ashore and in rockshelters and quarries.

I have seen many pictures of Moken kids, but not one that wore eyeglasses.
Today however, due to politics, economics and the 12/04 tsunami, their lifestyle has been grounded and "modernized", their diving has probably become marginalized, while schooling has increased.
DDeden