3 ms·

How would those events change the crystals within the lens of their eyes?

by kgwgk 7y ago

pvaldes 7y ago
Unlike us, fishes have continuous growing. And also unlike us, they do not use sugars. Its main source of energy is fat, that they store either in the whole body or in the liver. Sharks belong to the second group (something than was basic for the development of precision machines and robotics in fact). Being cold blooded species, fishes rely on the water temperature to warm itselves. When the temperature decreases under the viable range for its enzimatic gut activity, they stop eating, get sluggish and enter in "saving energy mode" until the circumstances got favourable again (instead to spend valuable resources chasing preys that they can't digest anymore). In a long migration through open sea they will cross extensive low-density preys areas and the result is similar. If the fat reserves eventually get depleted the fishes need to resort to its second and last source of energy: Proteins. They start burning muscle, recycling its proteins as fat and burning this fat. Fishes do this routinely when needed and can "de-grow" to some extent, shrink and recover quickly later. Sharks are particularly well adapted to alternate periods of feast and famine. In case of emergency, we can burn proteins in a similar way, but, unlike us, the weigh of aquatic animals is supported by water in part, so its skeletons are also reduced. Our skeletons are always saved until the last minute (We need it more than fishes need theirs). And this is the part used in carbon-14 tests. As proteins (like those in eye lenses) and fats are made of carbone, almost anything non indispensable in a fish body can be recycled and burn instead. Eyes are not essential structures for deep-water sharks (can rely in olfactory, electric and water pressure receptors instead), so if in a hurry, they can assign less resources for their maintenance. The result is that the eye lense will grow slower and with a lighter (cheaper) structure, therefore you have a more transparent area. A feasting period instead means some extra calcium (or other matherials) assigned to the eye maintenance. This is what makes the structure "readable" as a series of bands alternatively opaque and hyaline.
- kgwgk 7y ago
  They are looking at those proteins in the nucleus of the lens of the eye for a reason. Didn’t you wonder why? “In vertebrates, the eye lens nucleus is composed of metabolically inert crystalline proteins, which in the center (i.e., the embryonic nucleus) is formed during prenatal development (6, 7). This tissue retains proteins synthetized approximately at age 0 – a unique feature of the eye lens that has been exploited for other difficult-to-age vertebrates (6, 8, 9).” https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09/download_file?file_format=pdf&safe_filename=Eye%2Blens%2Bradiocarbon%2Breveals%2Bcenturies%2Bof%2Blongevity%2Bin%2BGreenland%2Bshark.pdf&type_of_work=Journal+article https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-99... “Because the epithelial basement membrane (lens capsule) completely encloses the lens, desquamation of aging cells is impossible, and due to the complete absence of blood vessels or transport of metabolites in this area, there is no subsequent remodelling of these fibers, nor removal of degraded lens fibers. [...] The lens fibre cells in the nucleus of an adult lens are thought to be produced during early embryonic life [2]. The lens plate is formed in the 4 mm embryonal stage. The lens fibre cells degrade all membrane-bound organelles and the older lens cells become compressed into the nucleus of the lens by the continuous formation of new fibres at the surface.” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001529 https://journals.plos.org/plosone/article?id=10.1371/journal...
  - pvaldes 7y ago
    Thanks for the links. It clears many things, but the main problem stills remain. Let me put you this example problem. "We have a box full of marbles and we can take two marbles out of the box each day. How many time it would take us to empty the box of marbles? As you had noticed yet, this is an unsolvable problem Now lets assume than we examine a Greenland shark's eye lense and register a value of "X" remaining radioactive carbon-14 atoms and then we take a look to a human eye lense of known age and found "Y" remaining radioactive C14 atoms. To simplify the problem we will assume that all atoms in a eye lense are trapped there forever, no new carbon atoms were physically added or removed, and the size, weight, and fiber density in the lense are the same for both human and shark. Having in mind that decay ratio is independent on taxonomy and there is not any reason to think that radioactivity would decay faster in a particular vertebrate... if X = Y; could we conclude than the shark and the human had the same age? The answer is: Not, we can't infer the shark age. And this is the same problem than with the box of marbles.

How would those events change the crystals within the lens of their eyes?

by kgwgk 7y ago

How would those events change the crystals within the lens of their eyes?

Unlike us, fishes have continuous growing. And also unlike us, they do not use sugars. Its main source of energy is fat, that they store either in the whole body or in the liver. Sharks belong to the second group (something than was basic for the development of precision machines and robotics in fact). Being cold blooded species, fishes rely on the water temperature to warm itselves. When the temperature decreases under the viable range for its enzimatic gut activity, they stop eating, get sluggish and enter in "saving energy mode" until the circumstances got favourable again (instead to spend valuable resources chasing preys that they can't digest anymore). In a long migration through open sea they will cross extensive low-density preys areas and the result is similar. If the fat reserves eventually get depleted the fishes need to resort to its second and last source of energy: Proteins. They start burning muscle, recycling its proteins as fat and burning this fat. Fishes do this routinely when needed and can "de-grow" to some extent, shrink and recover quickly later. Sharks are particularly well adapted to alternate periods of feast and famine. In case of emergency, we can burn proteins in a similar way, but, unlike us, the weigh of aquatic animals is supported by water in part, so its skeletons are also reduced. Our skeletons are always saved until the last minute (We need it more than fishes need theirs). And this is the part used in carbon-14 tests. As proteins (like those in eye lenses) and fats are made of carbone, almost anything non indispensable in a fish body can be recycled and burn instead. Eyes are not essential structures for deep-water sharks (can rely in olfactory, electric and water pressure receptors instead), so if in a hurry, they can assign less resources for their maintenance. The result is that the eye lense will grow slower and with a lighter (cheaper) structure, therefore you have a more transparent area. A feasting period instead means some extra calcium (or other matherials) assigned to the eye maintenance. This is what makes the structure "readable" as a series of bands alternatively opaque and hyaline.

kgwgk 7y ago
They are looking at those proteins in the nucleus of the lens of the eye for a reason. Didn’t you wonder why? “In vertebrates, the eye lens nucleus is composed of metabolically inert crystalline proteins, which in the center (i.e., the embryonic nucleus) is formed during prenatal development (6, 7). This tissue retains proteins synthetized approximately at age 0 – a unique feature of the eye lens that has been exploited for other difficult-to-age vertebrates (6, 8, 9).” https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09/download_file?file_format=pdf&safe_filename=Eye%2Blens%2Bradiocarbon%2Breveals%2Bcenturies%2Bof%2Blongevity%2Bin%2BGreenland%2Bshark.pdf&type_of_work=Journal+article https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-99... “Because the epithelial basement membrane (lens capsule) completely encloses the lens, desquamation of aging cells is impossible, and due to the complete absence of blood vessels or transport of metabolites in this area, there is no subsequent remodelling of these fibers, nor removal of degraded lens fibers. [...] The lens fibre cells in the nucleus of an adult lens are thought to be produced during early embryonic life [2]. The lens plate is formed in the 4 mm embryonal stage. The lens fibre cells degrade all membrane-bound organelles and the older lens cells become compressed into the nucleus of the lens by the continuous formation of new fibres at the surface.” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001529 https://journals.plos.org/plosone/article?id=10.1371/journal...
- pvaldes 7y ago
  Thanks for the links. It clears many things, but the main problem stills remain. Let me put you this example problem. "We have a box full of marbles and we can take two marbles out of the box each day. How many time it would take us to empty the box of marbles? As you had noticed yet, this is an unsolvable problem Now lets assume than we examine a Greenland shark's eye lense and register a value of "X" remaining radioactive carbon-14 atoms and then we take a look to a human eye lense of known age and found "Y" remaining radioactive C14 atoms. To simplify the problem we will assume that all atoms in a eye lense are trapped there forever, no new carbon atoms were physically added or removed, and the size, weight, and fiber density in the lense are the same for both human and shark. Having in mind that decay ratio is independent on taxonomy and there is not any reason to think that radioactivity would decay faster in a particular vertebrate... if X = Y; could we conclude than the shark and the human had the same age? The answer is: Not, we can't infer the shark age. And this is the same problem than with the box of marbles.