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Why do turtles live long?

Jonathan (hatched around 1832) is the male aldabra tortoise who lives on the island of St. Helena in the British Overseas Territories in the Atlantic Ocean. Jonathan can be considered the oldest known tortoise of the living and the oldest known living land animal in general.

If to answer very shortly, the turtles live a long time, because they are a) cold-blooded and b) large. Let us explain these two answers.

Life is supported by chemical reactions. To the creature remained alive, the chemicals in it must constantly turn into each other, or, as they say, exchange. The speed of these transformations, or metabolism, is directly related to how active the animal can be, how much food it needs to eat, how much it needs to sleep and how much it will live.

The rate of metabolism depends on the size of the animal. In small animals, the surface of the body is large relative to the volume, and with increasing size of the animal, the surface area grows slower than its volume. For example, an elephant has about 0.03 square centimeters of the body surface per cubic centimeter of body volume, and the hamster has as much as 0.6, that is, 20 times more. Through this large surface, the heat dissipates, which the hamster carefully produces, so the hamster has to eat and burn many more nutrients per unit of body weight than the elephant. The metabolism of the hamster inevitably goes faster, because it eats a lot and generates a lot of heat, and from the processed food it is quickly disposed of and immediately absorbs the new one.

Animals with rapid metabolism are more active (when they are not sleeping), because they produce a lot of energy and because they need new food all the time. At the same time, they need to sleep more, because the toxic by-products of the work of neurons accumulate faster in their brains, to get rid of which, apparently, a dream is needed. If small rodents sleep up to 20 hours a day, then elephants – only 3-5 hours.

Vertebrate animals with a slow metabolism (that is, large animals) live longer than animals with rapid metabolism – this is a well-known pattern. Records of life expectancy among vertebrates – this is the whales, elephants and Galapagos tortoises, also quite large and growing, apparently throughout life.

Why with slow metabolism can live longer than with fast metabolism, this is not such a simple question. The answer is somehow related to the accumulation of damage and aging, which occur faster in animals with rapid metabolism, but not quite directly. For example, small rodents naked diggers are famous for their lack of signs of aging and resistance to cancer (which can occur due to a variety of injuries). But even without aging and with remarkable resistance to damage, these animals live no longer than 30 years. This is much more than the average life span of other animals of this size (which is about two years), but still significantly less than the average durations of large animals that are not free from aging. In theory, naked diggers could live until,

The most reasonable assumption is the balance of births and deaths, which should be maintained in the population. At some point, any individual must die to free the living space for a new, more adapted generation. But she must do this at a certain moment, in accordance with her speed of reproduction. In animals with fast metabolism, compared to the rest, life passes as if in an accelerated survey – they live it faster, but also more actively, leaving a large number of offspring in a fairly short time. Therefore, they quickly cope with their task members of the population and quickly free up space for a new generation. Elephants or other large animals multiply much less often than small animals and bring less offspring. Their lives seem to be slowed down, so they need to live longer in order to catch everything.

Likewise, the life of cold-blooded animals is slowed in comparison with warm-blooded animals. Cold-blooded animals do not spend resources on maintaining a constant high temperature and body, and hence, a high rate of exchange. Therefore, the exchange rate for them is as lucky: if the lizard is basking in the sun, it will be more active, and if not, then it will have to slow down a little. But on average, the rate of metabolism in cold-blooded animals is always lower than in warm-blooded animals, because it is not always sunny, and it is usually not easy to heat up in the sun to such body temperatures as in mammals or birds. Therefore, the life of cold-blooded animals is even slower than in warm-blooded animals.

The tortoise is a cold-blooded animal, and the turtles do live quite a long time. But the big turtles – the inhabitants of the Galapagos Islands, combine the slowness of the exchange of large animals and cold-blooded animals. Such a successful combination allowed them to set a record among vertebrates (if we take well-documented evidence) – 177 years of life.

But turtles should not be jealous, because, as already mentioned, their metabolic rate differs from ours. The rate of metabolism is associated with a sense of subjective time: the higher it is, the slower the perception of the animal in the world around. This speed of individual time can be determined by measuring the minimum frequency of flashes of light, from which the light begins to be perceived as continuous, the so-called critical flicker frequency (CFM).

How do we study the critical frequency of flicker fusion (CSFM) in animals

The animal is placed inside a transparent drum with vertical dark strips on the walls. Outside, another one of the same drum is placed, which can rotate at the required speed. The construction is illuminated by a bright light source.

Apparatus for measuring the critical frequency of flicker fusion (CSFM) in lizards. Image from the article TA Jenssen, B. Swenson, 1974. An ecological correlate of critical flicker-fusion frequencies for some Anolis lizards

Due to the rotation of the outer drum relative to the inner in the animal, it is felt that it has entered the rotating room and it makes movements as if trying to stay on the rotating floor (or, if the experiment is carried out on the fish, they make movement as if they were in a rotating current ). But beginning with a certain frequency of rotation of the drum, the animal ceases to notice the flickering of strips on the walls of the drum and ceases to behave as if it were in a rotating room. The corresponding frequency is the critical fusion frequency for the investigated animal.

In humans, this number is on the average 60 flashes per second, and the tortoise has 15. This means that according to the sensations of the turtle, the time goes 4 times faster than for a person: during a time for which a person manages to notice 4 flashes, the tortoise can notice only one.

It is easier to imagine this with the example of flies, in which KCMM is 4 times larger than in humans, 240 flickers per second. It seems to a person that he quickly flies a fly on a fly, but for a fly his movement looks very slow, so it is almost impossible to get to it. And on the outside everything looks the other way around – an animal that seems to be flying fast, moving slowly.

That is, 177 years for a turtle – it’s not so much.

So the first thing you can learn from this story is that turtles should not be jealous. The second, slightly less obvious, is that reducing the calorie content of food can increase life expectancy. Indeed, the more nutrients we process, the higher the metabolic load on our body. It does not pass without a trace, especially in those animals that, unlike naked diggers, are aging, and do not possess incredible resistance to damage. It is especially insulting to process the extra calories that most modern people who lead a sedentary lifestyle do not need. Experiments to limit the calorie content of food were carried out in mice and rats, as well as some fish and monkeys, and produced good results. In mice, for example, the average and maximum longevity could be increased by 30-50%The Effect of Retarded Growth Upon the Length of Life Span and Upon the Ultimate Body Size: One Figure .

Answered: Julia Kondratenko

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