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Science reveals why turtles live so long

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the terrestrial animal oldest in the world is Jonathan, a giant turtle who lives in the Seychelles archipelago and who turned 190 a few months ago. It is estimated that born about 1832although since there was no record it could have done so even earlier.

Jonathan is also the longest living reptile in history. However, his is not the only case. Some species of turtles and other ectotherms (cold-blooded animals) are known to have a extraordinarily long life.

In fact, the magazine Science publishes this week two independent studies on the aging and life expectancy of these long-lived animals. The first of them, carried out by researchers from the University of Southern Denmark (SDU), has analyzed tortoises of 52 different species that live in zoos and aquariums in many countries.

“In general, evolutionary theories of aging have been made about mammals. That is why it has been possible to verify that this process exists in them and in birds, but this has not always been verified in reptiles and amphibians, which have very different life cycles and survival strategies”, explains Fernando Colchero, co-author of the study.

The second investigation, which brings together an international team of 114 scientists led from the USA, has studied reptiles and amphibians of 77 different species that live freely in more than 100 populations around the world.

“If we can understand what allows some animals to age more slowly, we can better understand aging in humans, and we can also define conservation strategies for reptiles and amphibians, many of which are threatened or endangered,” explains David Miller, lead author of the University PennState.

Turtles in zoos and aquariums

For their part, experts from the Danish university have observed that 75% of tested turtle species show extremely slow senescence and, in some cases, even the lack of biological aging, which is defined as negligible.

The term insignificant senescence was coined during the last century by biogerontologist Caleb Finch to denote organisms that show no evidence of biological aging, such as measurable reductions in reproductive capacity or increases in mortality rate with the age.

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As explained by Dalia Conde, another of the authors of the first study, many species of turtles can reduce their rate of aging in response to better conditions of life in zoos and aquariums, compared to the wild.

This means that senescence it’s not inevitable for all organisms”, comments Rita da Silva, first author of the article.

In primates, including humans, the improvement of environmental conditions determines a decrease in infant mortality, but aging rates do not change or change very little. This is very typical in many groups of mammals and we believe that possibly also in birds, but it was not the case with turtles”, adds Colchero.

Growth after sexual maturity

According to some evolutionary theories, senescence appears after sexual maturity as an exchange between the energy that an individual invests in repairing damage to their cells and tissues, and the energy that they contribute to reproduction so that their genes are passed on to the following generations.

This compensation implies that after reaching sexual maturity, individuals stop growing and begin to experience senescence, the gradual deterioration of bodily functions with age. Before, the consensus was that the most complex organisms could not stop aging. However, there are species, such as many turtles, that in sexual maturity continue to grow.

“It is surprising that in turtles and in many reptiles they not only manage to reduce the rate of aging, but also their ability to reproduce increases with age. For example, the number of eggs that a female tortoise can lay when she has just reached sexual maturity is only a fraction of what she can lay when she is older,” insists Colchero.

Keep in mind, however, that the fact that some animals show negligible senescence does not mean that they are immortal: your risk of death does not increase with age, but is still greater than zero.

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“Although these animals are not exposed to certain potential causes of death when found in zoos and aquariums, all of them will die at some point due to unavoidable causes, as diseases”, he emphasizes.

Reptiles and amphibians living in the wild

In the same way, the authors of the second study document how several animals have particularly low rates of aging; in addition to turtles, also crocodiles, salamanders and toads, among others.

“It sounds very drastic to say that they don’t age at all, but basically once they’ve stopped reproducing their probability of dying does not change with age”, points out Beth Reinke, a researcher at the Northeastern Illinois University and first author of this work.

The objective of this research was to analyze the difference in aging and longevity between ectotherms and endotherms (warm-blooded animals) that live in freedom.

In the ectothermic animals, the body temperature varies according to the external (environmental); Reptiles and most fish are examples. The endothermsInstead, like humans and all mammals, they internally generate their own heat and thus regulate their body temperature regardless of that of the external environment.

Miller explains that the hypothesis of thermoregulatory mode suggests that ectotherms, which use external temperature to regulate their body temperature and thus often have lower metabolisms, age more slowly than endotherms. “People tend to think, for example, that mice age fast because they have a high metabolismwhile turtles age slowly due to their low metabolism”, indicates the researcher.

However, the way an animal regulates its temperature is not necessarily indicative of its aging or longevity. “We found no support for the idea that a lower metabolic rate implies that ectotherms age more slowly. That relationship is only true for turtles, suggesting that they are unique among ectotherms,” he concludes.

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Environment section contact: crisisclimatica@prensaiberica.es

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