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Biology

Eli5: How can certain animals such as frogs and flies freeze solid and survive, but most mammals suffer extreme tissue damage?

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At least part of the answer is that some animals evolved ice-binding proteins or antifreeze proteins. These proteins prevent the growth of ice crystals which can rupture cells.

so wee need to modify ourselves with those proteins to enable cryo-sleep, got it!

First step... Drink antifreeze

Done. Now what?

Call 911 or your local Poison Control centre.

You guys crack me up. First chuckle of the day. Thanks.

Same here, as my day started like 30 minutes ago

This guy chuckles.

That's pretty much what they already do for cryogenics; the hard part continues to be bringing them back to life.

Didn't they do that to Solid Snake in Metal Gear Solid? Gave him an antifreezing peptide?

Also, to be fair this is a very delicate mechanism - they too can suffer tissue damage/death if the process fails. While they are better equipped, they are not infallible.

1 point·3 months ago·edited 3 months ago

Meh, as a stickler for wording in explaining evolution I'd modify your explanation.

It's not that they evolved it to survive, it's that only those that could survive in those conditions were able to procreate and pass on their genes.

Let's say for example that our entire population were subjected to a plague that destroyed our immune systems resulting in our death, except that there is a small percent of the population that survives. Those individuals did not evolve to survive a plague, but they all shared a genetic mutation that prevented their deaths (an immunity, a counter-agent, who cares - the point is it's in their DNA and they were already born with it). Now if those survivors have offspring, while we do not know how dominant that gene is (like Brown eyes and Blue eyes), we do know there is a chance their offspring will inherent the dominant version of that gene and also survive (and there is a chance they will only get a recessive version and may still die).

Later on we aren't going to say that humans evolved a way to survive, because that wording (which always bugs me) implies that our bodies are making a choice, but they're not. We simply get lucky to be born with mutations that allow us to survive/procreate better. Evolution is simply the process by which only those able to survive their environments are able to produce offspring who in turn pass on their favorable genes.

So that all is to say that frogs/crocs etc have survived the freezing cold because throughout the last millions of years, these types of dramatic climate changes have happened and those that couldn't survive would have died off a lonnnng time ago. Only those that had genetic mutations such as the ice-binding proteins and antifreeze proteins mentioned above, survived and thus passed on those genes to their offspring.

The main danger with freezing is that the ice crystals that form poke holes in the cell membranes. Without functional cell membranes there is nothing (or at least not enough) to keep your cell-stuff in place and the cell dies pretty quickly. This is also how all antibacterial chemicals like soaps and alcohol work (NOT antibiotics).

Antifreeze prevents the formation of these ice crystals, or at least keeps them limited in some way that they do less or no damage to the cell membranes. This is actually used in microbiological labs; if you want to freeze your cells or bacteria, you put them with a bit of some specific antifreeze component.

Unfortunately for most cells and bacteria antifreeze is also very toxic. But, some animals have evolved components that act with a similar function as antifreeze.

Original Poster3 points·3 months ago

So the answer is that they simply don’t freeze? So this also would prevent tissue damage from the fluid expanding as well I presume?

So if the temperature drops lower, it would probably kill the animal?

I'm not 100% on the first part, but the last part? Yes.

Proteins (the little machines that do nearly everything in cells) tend to only work at specific temperatures. Outside of their goldilocks range, they can unfold or wrongly fold themselves, which can permanently ruin them. That's what makes eggs turn opaque and relatively solid when you cook them.

We don't know! I'm working in a lab right now studying insects that can survive being frozen. They have certain characteristics that can control ice crystal growth which probably helps.

Do these characteristics prevent ice crystal formation or cause the water to freeze in crystals small enough that they don't puncture cells?

It has more to do with the size of the animal, and protection it may have from damage caused by freezing.

It takes longer to freeze a pound of meat, than a hot dog due to mass and how thick it is affects length of time for the center to cool. A gentleman by the name of Birdseye discovered that food frozen in the beginning of winter, often preserved worse than food frozen during the height of winter. He came up with the concept of flash freezing produce to ship from farm to peoples homes.

What they found was that the faster something freezes, the smaller the ice crystals are, which limits cellular damage. Freeze a frog, or an ear of corn, slowly, and ice crystals turn the flesh to mush. Flash freeze them, and they are still 'fresh' when thawed, and crisp and intact.

the frogs that can freeze and thaw, have very small bodies, so that helps with time it takes to freeze, but it also helps with time it takes to thaw. The limbs of the frog will thaw first, while the center of it's body will still be frozen. Limbs without a beating heart will quickly begin to suffocate so thawing requires this doesn't go on too long. The physical size of the frog helps with that and it tends to thaw pretty evenly.

A mammal could similarly survive a freeze but it would have to be small enough to freeze quickly, much smaller than a mouse, and it would benefit from cellular antifreeze which is seen in some reptiles and fish, but not mammals yet. Not that it wouldn't work in mammals, just that mammals evolutionary niche is to go into low energy mode during winter, or hibernate, rather than to freeze, so evolution hasn't really selected for it.

I'd love to see any sources on this. You are being purely speculative. Mammals could never freeze and survive, we have completely different metabolism than ectothermic insects and frogs. Yes, the size and quality of ice crystallization may matter, but it's got nothing to do with the size of the organism

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