Why do tortoises live so long?

[Terry Allan Hall]

Didn't dolly the sheep have shorter telomeres which caused her shortened life span?

As I understand it (from a show I saw a few years ago on The Science Channel), a clone is an exact replica of the "donor" animal at that age, so a clone of, say, a 21-yo male is born w/ the age of 21 already in his genes...thus he'll age sooner (a clone of a 21-yo will be about biologically 70 when he's 50, in other words).

As I recall, Dolly is how they figured this out...

 

[Angi]

I am with Jacob on this.

 

[mctlong]

My non-scientific answer - They have the same amount of life in them as any other animal, but they just use it very very slowly.

 

[Terry Allan Hall]

My non-scientific answer - They have the same amount of life in them as any other animal, but they just use it very very slowly.

A Buddhist priest once told me that all living things get the same number of heart beats...those who use them up the fastest die the soonest.

Interesting perspective.

 

[dmmj]

My non-scientific answer - They have the same amount of life in them as any other animal, but they just use it very very slowly.

A Buddhist priest once told me that all living things get the same number of heart beats...those who use them up the fastest die the soonest.

Interesting perspective.

So if I stop my heart I will live forever?

 

[Terry Allan Hall]

My non-scientific answer - They have the same amount of life in them as any other animal, but they just use it very very slowly.

A Buddhist priest once told me that all living things get the same number of heart beats...those who use them up the fastest die the soonest.

Interesting perspective.

So if I stop my heart I will live forever?

Doubt it really works that way, so may I suggest that you find someone else to test your theory upon, first...maybe a politician or a televangelist, or someone equally "non-essential"...

A world w/o a Captain Awesome is a bleak world, indeed, to consider!

 

[Yvonne G]

A world w/o a Captain Awesome is a bleak world, indeed, to consider!

Indeed!

 

[Tccarolina]

Very interesting topic, GeoTerraTestudo and HLogic, the two of you have explained telomeres make more sense than any of my college biology teachers did!

I'd like to add that the herbivorous diet and size may not matter much in tortoise/turtle longevity, as american box turtles and snapping turtles may last as long as the oldest of the big tortoises. Also, aren't their records of Hermann's and Greek tortoises reaching old ages, 150ish in Britain? Of course, great age has only been verified in a few cases.

Steve

 

[bikerchicspain]

I Think They Live Long, Because They Eat Healthy and Mostly Vegetables!
Also In The Wild if They Are Scared Or Stressed Out They Can Hide in There Shell Which Makes
There Life prettyy Peaceful!

My thoughts exactly, they eat healthy, the temps are perfect, humidity perfect,and because they are not an animal that gets handled,cuddled, taken out for walks or for a beer
there stress levels are minimum.

 

[Madkins007]

I am not sure I would call the life of a wild tortoise 'low stress'. Certainly, the documented long lives in captivity are pretty stressless, but the life of a wild turtle or tortoise is about as stressed as any other species. Most turtles and tortoises serve as prey for SOMETHING in their habitat- full adult Red-foots are a major part of the jaguar's diet in some parts of South America.

Some other tortoises live in such marginal places that they are on the edge of starvation or dehydration much of the time. Making a desert tortoise release the water stored in its bladder is a death sentence in some seasons.

There is a reason tortoises are so well camouflaged and spend so much time hiding in protected shelters- even with their shells. Because they are so slow and have no real offensive weapons, any animal that can break, pierce, or bypass the shell can eat the poor things.

 

[Saloli]

Ah, a biology discussion. Yippee! My specialty. Okay, pull up a chair and let's get started.

When thinking about how long an organism lives, there are two levels to look at. The first is the proximal level, or the immediate mechanism by which an animal is able to do what it does. As Mark said, turtles do have certain characteristics that allow them to lead long lives. The second level is the ultimate level, which accounts for the evolutionary pressures that helped shaped the animal into what it is today. Since Mark covered the proximal causation above, I will now cover the ultimate causation. In ecology, the length of time an organism lives and the number of offspring it has are considered together as a life history strategy. And the theory that explores why certain plants and animals have the life history strategy they do is called r/K selection theory.

Some organisms are known as r-strategists because they operate near r, which is the maximum reproductive rate. Such plants and animals do not get very big, lead short lives, and leave behind a whole bunch of small and simple, but precocial (well-developed) offspring before they die. Good example of r-strategists are flies in the animal kingdom, and weeds in the plant kingdom, which meet most of the criteria above. They grow fast, they reproduce, and they die young. This is how their lines survive through the ages. Other organisms are called K-strategists because they have evolved near K, or the carrying capacity of the environment to support them. In other words, these creatures have evolved to use scarce resources efficiently, but also to wait a long time before they can reproduce. These organisms leave relatively few offspring and invest heavily in their development and care. A great example of a K-strategist plant would be a sequoia tree, and a great example of a K-strategist animal would be an elephant. Both of these organisms live a long time, get huge, and don't reproduce that often. In the case of the elephant, there is a tremendous amount of investment put into one offspring. Elephants have the longest pregnancies in the world at around 2 years. They reproduce only once every 4 years or so, and they give their offspring a lot of care and attention. Big contrast to cockroaches, isn't it? In reality, there is a spectrum between these two extremes. Very few organisms are entirely r-selected or entirely K-selected. Most plants and animals have some adaptations in response to r, and other adaptations in response to K.

That's how it is with turtles, which are kind of in between, but probably a bit closer to the "K" end of the spectrum. On the one hand, they lay many eggs and don't give them much parental care beyond finding a good spot for them (except for Manouria, which does exhibit some parental care by guarding the nest - kind of like a crocodile). Turtles hatchlings are the poster children for the concept of "Nature red in tooth and claw." Many of them get gobbled up by predators shortly after they hatch, and many more get eaten before they ever reach adulthood. Only a small percentage actually go on to have offspring of their own. On the other hand, turtles have evolved to take advantage of scarce resources by growing as big as possible before reproducing. So, they reproduce only once they have gotten to be relatively large and relatively old. Depending on the species, it can take many years until a turtle is finally ready to mate and lay eggs. This is actually true for a lot of large, egg-laying vertebrates. Turtles are actually kind of like sturgeon, which are some of the biggest fish in the world. Both turtle and sturgeon wait until they can get as big as they can so that they can really produce a lot of eggs. The more eggs they can produce, the better their offspring's chances at survival. Of course, even with the turtle order, there is a spectrum from r- to K-selection. The bigger the turtle, the more K-selected it is. This is true both in the water and on land. Small species don't wait as long to reproduce, and don't get to be as old, on average, as big turtle species. But when you compare them to other similarly sized reptiles, all turtles are close to the "K" end of the spectrum.

So, to answer your question, the reason tortoises live so long is so that they can produce the greatest number of healthy offspring they can, and so they can maximize their offspring's odds of surviving to adulthood and repeating the process.

BTW - There used to be more species of huge turtles in the world besides Galaps, Aldabras, and modern sea turtles. These giants were even more on the "K" end of the spectrum than most of today's smaller turtle species. But as I mentioned in an earlier post, some of these went extinct only a few thousand years ago. This was probably because, although their shells gave them great protection against cats, dogs, bears, etc., they were no match for humans and their tools. Archaeological evidence indicates that people used to flip 1-ton tortoises onto their backs, light a fire under them, and cook them in their own shell. Being essentially K-strategists, these giant tortoises' reproductive rate could not keep up with the rate at which people were eating them, so they went extinct. This is the risk of being a K-strategist: you have great adaptations for taking advantage of scarce resources, but if conditions change (like the arrival of a new predator, such as humans), you could go extinct.

Oh wow someone that understands selection theories. The r/k theory is still valid though there have been modifications (I'm a horrible speller dispite having passed english compostion and the other class on writting formal reports with a's). Sorry I don't often run into people in the the pet side of herpetoculure (I don't think that is correct) that understand the scientific principles. Though Terrapene aren't tortoises they match and exceed many in known ages of wild and captive individuals. Turtles also are very good a reparing telomeres, which means chromasomes stay in working order longer. Oh and by the way birds are technically reptiles in that they are theapod dinosaurs and thus archasaurs like crocodilians.

 

[zesty_17]

So, Geo- maybe you know this... I understand that DNA has a snippet that basically causes the strands to self-destruct over time. As primitive as chelonians are, do they have this bit?

That's right. All vertebrates - from fish to humans - have their DNA bundled up in chromosomes. The tips of these chromosomes have a tendency to unravel over time, causing aging-related health problems. For this reason, all vertebrates have telomeres on the ends of their chromosomes to keep them from unraveling. These telomeres are basically long, repetitive sequences of DNA bundled up with proteins called histones, that allow the chromosome to resist unraveling. The telomeres are very much analogous to the shoelace caps at the ends of shoelaces; without them, the shoelaces tend to turn into thread with repeated wear. Likewise, telomeres prevent chromosomes from exposing their DNA, thereby reducing the likelihood of mutations, as well as allowing the DNA to continue coding for necessary proteins as normal.

However, not all telomeres are equally effective. Humans, for example, with our 70+ year lifespan have telomeres that are reasonably good, meaning that they are relatively thick and resist wear and tear, but they are not perfect. This is one reason we tend to develop illness as we age (another reason is glycosylation, or the "gumming up" of our cells with excess sugars). Other animals have very thin and inefficient telomeres. Many rodents and carnivores, for example, only live a few years, so their telomeres are pretty minimal; that's all they need to be.

Other animals, though, have terrific telomeres. Many types of long-lived sharks and fish have very thick telomeres that take a very long time to break down. This is one reason why sharks don't develop cancer. They rarely experience any unwanted mutations, and their DNA functions normally throughout their lives. Animals like this experience little to no senescence, meaning that they get older without really getting particularly old (although they do eventually die, of course). I have not looked into telomere size in turtles specifically, but I betcha they must be quite hefty to allow a Galap to live for 150 years or more with little if any illness until his time finally does come.

But again, there were evolutionary pressures in animals like tortoises that caused them to develop these protective mechanisms, which in turn allow them to live for a long time. It is adaptive for a tortoise to experience little senescence, while a rat, for example, experiences significant senescence in captivity if it lives much longer than it would in the wild. Even in the absence of predators, rodents still don't live very long. They don't have the adaptations to give them long life, because in nature they don't need them. Tortoises, meanwhile, have a completely different suite of adaptations to help them live much longer.

There was an article about this back in 2003/4? It specifically spoke about the giant torts and longevity and cellular breakdown. If i find it, i will post on here.