Why do tortoises live so long?

[dmmj]

I have often pondered this question, and I really can't find an answer. Plus it seems like the bigger the tortoise the longer they live. Anyone got any answers? any theories? does anyone actually have the answer? I have heard lots the most common one is that their slow lifestyle leads to a longer life, but I have not seen any evidence one way or the other. One other one I think I have seen on here, is that turtles and tortoises don't die form old age just bad care and injury. So people lets get it started.

 

[Madkins007]

are multiple things going on here.

1. MOST chelonians do not live an extraordinary length of time. 30 years is considered about average for many species. In general, the largest are also the longest lived- but they also have the fewest predators (point 4).

2. As a rule of thumb, herbivorous species live longer than predatory ones. Meat eating is associated with lots of diseases and risks.

3. Slow metabolisms AND a slow, sedentary lifestyle means every metabolic process, including the simple aging of DNA, happens more slowly. This is one of the top issues.

4. Lack of predators. One shared trait of most of the longest-lived chelonians is a lack of predators or man-made hazards. They have been in zoos, remote areas away from cars, etc. One of the longest-lived box turtles known was from an area where most of the natural predators had been hunted out a long time ago.

 

[dmmj]

So the larger tortoises don't live longer because they are larger, but because they have less predators?

 

[Jacob]

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!

 

[October]

So the larger tortoises don't live longer because they are larger, but because they have less predators?

Or they live longer because they're bigger which makes fewer predators?

(Since Madkins said everything I was thinking, I'm gonna ramble) To me, it seems that torts are incredibly proficient at adapting to their environments once they reach a certain age/size. I don't mean that at 5" all the sudden that tiny, cold, dry aquarium is the perfect place for them. But more along the lines that either they die young from situations that do not facilitate good health or they are in a place that just meets the threshold of sustainable life and they just age right through it. And hopefully something changes and they are able to thrive again. But their ability to "conserve" themselves seems to have something to do with it.

Wow, does that even make sense? It's been 2 really rough weeks here. :/

 

[GeoTerraTestudo]

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.

 

[ALDABRAMAN]

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 first thoughts also, Low stress and great diet!

 

[Madkins007]

Low stress and great diet can play a role, but tortoises do not generally live in places with an abundance of high quality food. In most of their ranges, tortoises work hard to find enough nutrition and water to stay alive. Picking up a wild desert tortoise and making it urinate out of stress is pretty much a death knell.

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?

 

[dmarcus]

I can't add anything to this, but I sure have learned a lot from just the few post's already. Great thread!!!

 

[GeoTerraTestudo]

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.

 

[DocNezzy]

Great thread. Very informative.

 

[dmmj]

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

 

[Zouave]

One word .... "Obamacare"!

 

[Mao Senpai]

This has been very informative!

 

[GeoTerraTestudo]

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

Bingo. Dolly was cloned from the udder of a ewe that was already several years old. Thus, her DNA was not the "brand new" DNA of a newborn lamb, but rather the older, somewhat unraveled DNA of an adult sheep. And indeed, she started showing signs of senescence at a much younger age than most sheep do. In other words, Dolly was "born old," and this was due largely to the fact that her telomeres did not last as long from birth as they do in most sheep.

 

[HLogic]

Sorry to jump late into this thread but...

Didn't Dolly and several of her flock die of a form of lung cancer caused by a retrovirus prevalent in sheep kept indoors? Was there any evidence that telomere shortening or 'advanced' senescence played a role in her demise?

Didn't the r/K Selection Theory fall out of vogue some 20 years ago? Not to say that some of its posits are not valid but there was no experimental proof and even some experimental proof that demonstrated the opposite.

It seems that as much progress as has been made in the fields of genetics and genetic gerontology there is still a considerable amount to learn.

What is generally accepted is that telomere shortening is a normal, expected and desired behavior in most cell types. At a certain point, the shortened telomere triggers a 'cease and desist order' and the cell stops dividing or dies. This action prevents errors in DNA replication from proliferating which would cause the production of malformed proteins and associated problems.

When telomere shortening is prevented or reversing telomere shortening through the activation of telomerase (an enzyme that 'repairs' telomeres) occurs uncontrolled cell division is a potential result - the same action as occurs in many types of cancers (telomerase activation is found in ~90% of cancers). Luckily, telomerase is not normally found in somatic tissues with the exception of germ cells and some stem cells. So, long telomeres are a problem, right? Well, that's only the half of it, apparently short telomeres can indicate a predisposition to certain cancers in addition to the expected senescense. HUH??? Short AND long telomeres are bad? Very likely... As with most biological systems, there are normal ranges. It seems that telomere length may also fall into this category.

So then, if right-sized telomeres are the right thing to have, perhaps there is something else playing a part in this story. There are proteins associated with telomeres (TRF1, TRF2, ORC2 & ORC4). There are maintenance mechanisms for telomeres (telomerase). There is even RNA (TERRA) associated with telomeres and their maintenance. All of these play a role in DNA replication - as if you needed to be told!

Of course, there are other mechanisms at play in genetic maintenance and expression, too. 'Supervisor' proteins that control the expression of certain genes (FoxO). There are other non-genetic factors (although ultimately and intimately related to genetic expression) such as steroids (DHEAS) and many other players on the field as well. Some of the intermediate products (peroxide, hydroxyl & singlet oxygen) of normal cell respiration alter nucleic acids, proteins and lipids contributing to senescence. Exogenous free radicals can also have similar effects.

Enough already!!! Currently there are about 300 senescence-related hypotheses. Obviously, many touch on parts of the true process as they can be shown to measure certain aspects of senescence in vitro and in vivo. Thus far, a single hypothesis has not shown proof that encompasses cellular, organ and somatic senescence. It is unlikely that a single factor is at play and that many processes are involved over extended periods of time that ultimately result in what we know as old age and finally death. BTW, the mechanisms of aging in one life form are almost always inapplicable in another. In short, there is a lot left to learn...

Oh yeah, why do tortoises live so long? As it turns out, most lower vertebrates (fish, amphibians & reptiles) live longer than similarly sized higher vertebrates (birds, monotremes & mammals). There are exceptions. They also seem to be able to avoid the age-dependent fecundity barrier better or simply do not have that barrier. There are exceptions. Additionally, it is known that limiting caloric intake during infancy extends life expectancy in many organisms - no better diet plan than that of a tortoise! The same does not apply to humans... Genetics and gene expression, metabolism and energetics, environment and evolution (and many other -ics, -isms and -ions) all played parts in the development of processes that relate to senescence or the lack thereof.

There is an interesting article of study done with reptiles and in particular chelonians. While reading this bear in mind that in vitro cultured human fibroblasts have a 60 - 80 division (replication) limit.

Reptile Age (and then some) <== Click here!

Oh so much to learn!

 

[GBtortoises]

I have a few opinions on why tortoises live so long:

1) They're not married.

2) They don't have teenagers.

3) They don't smoke, drink or drive fast cars.

 

[stells]

That is probably quite true!!! LOL

I have a few opinions on why tortoises live so long:

1) They're not married.

2) They don't have teenagers.

3) They don't smoke, drink or drive fast cars.

 

[GeoTerraTestudo]

Didn't Dolly and several of her flock die of a form of lung cancer caused by a retrovirus prevalent in sheep kept indoors? Was there any evidence that telomere shortening or 'advanced' senescence played a role in her demise?

The Roslin Institute insists that Dolly's demise was due to disease typical to normal sheep, but I don't buy it. I think she was born old.

Didn't the r/K Selection Theory fall out of vogue some 20 years ago? Not to say that some of its posits are not valid but there was no experimental proof and even some experimental proof that demonstrated the opposite.

It is true that life strategy theory has been developed and expounded upon. The r- and K-strategies are not dichotomous, but rather lie on a spectrum. They are still considered valid concepts in ecology and evolutionary biology, and I use them almost everyday.

HUH??? Short AND long telomeres are bad? Very likely... As with most biological systems, there are normal ranges. It seems that telomere length may also fall into this category.

That's very interesting. I did not know that there is a Goldilocks, just-right telomere length. That does make sense, though.

In short, there is a lot left to learn...

Yep, glycosylation, oxidation - all of these are forms of wear and tear on the body at the molecular level, and they all count.

Oh yeah, why do tortoises live so long? As it turns out, most lower vertebrates (fish, amphibians & reptiles) live longer than similarly sized higher vertebrates (birds, monotremes & mammals).

Yes, metabolic rate may have something to do with it. For a given body mass, a fish, amphibian, or reptile needs about 1/10th as much food as a bird or mammal. This has implication for aging, because that means you are not giving off as many free radicals, so your cells are not going to suffer as much oxidative stress. As you said, there are a lot of factors involved, but metabolic rate does seem to be important.

BTW - Monotremes, marsupials, and placentals are all included in Class Mammalia.

Thanks!

 

[wrmitchell22]

I have a few opinions on why tortoises live so long:

1) They're not married.

2) They don't have teenagers.

3) They don't smoke, drink or drive fast cars.

Lol, you have figured it out, good job!