Two studies that analyzed dozens of species of reptiles and amphibians indicate that there really is something very special about the longevity of turtles. The vast majority of them, it seems, age very slowly or not at all—at least not in the way that humans get older.
The conclusions of the research have just been published in the specialized American journal Science, one of the most important in the world. If the observations are correct, this is an important contribution to the debate about the nature of aging, considered one of the great mysteries of biology.
It turns out that it’s not entirely clear whether so-called senescence (as experts call the process) is inevitable in the case of creatures such as animals, or whether, in some cases, it happens in a much less predictable and inevitable way. Discoveries on the subject may have important medical implications, especially at a time when the proportion of elderly people in the world population has become increasing.
In one of the studies, led by Beth Reinke, from the University of Northeastern Illinois (USA), researchers studied 77 species of reptiles and amphibians in the wild, through studies of capture, tagging and release over time, in periods with average duration of 17 years (reaching, in some cases, six decades). That is, the animals were captured, marked and, if possible, recaptured in the future for further analysis.
The second research, whose first author is the Portuguese Rita da Silva, from the University of Porto, studied turtles that live in zoos and aquariums and belong to 52 different species. In this case, it was possible to analyze records about the entire life trajectory of the animals.
Turtles, of course, are obvious candidates for the rank of vertebrate Methuselah, thanks to their known longevity. But expanding the range of analysis to a wide range of reptiles and amphibians is interesting because it makes it possible to take into account a series of characteristics that can influence longevity.
Among these possibilities are, for example, ectothermy (the popular “cold blooded” of these animals). This type of metabolism, generally slower than that of animals such as mammals, could, in theory, lead to slower wear and tear of the body’s cells and tissues. Other potentially important features are the presence of body armor (as, of course, in the case of turtles) and the ability to inoculate poison.
In both cases, these are characteristics that considerably increase the defensive capacity of the species that possess them. With this, in theory, the animal can adopt a more peaceful life cycle, with less “hurry” to reach sexual maturity and reproduce – and this, therefore, should translate into greater longevity.
Indeed, the reproductive cycle is another crucial point. Apparently, animals that tend to have young at an early age age faster than those that go through a long period of growth before mating for the first time. The idea is that the organism needs to “choose” where to invest its energies: rapid reproduction or longer growth. In the first case, rapid aging would be just a by-product of the fact that the body does not have the energy to spend on the constant “fixing” of its molecules.
The first study showed clear evidence that factors such as the presence of armor and the delay in reaching reproductive age are indeed important for longevity, putting tortoises in an enviable position (along with tuataras, extremely primitive New Zealand lizards that can also one hundred years of life).
The second study used statistical analysis to show that, contrary to what happens with humans, 75% of turtle species do not experience an increase in their mortality rate as individuals get older. This corresponds to a very low or “virtually undetectable” senescence rate, Rita da Silva told Sheet. Which is not the same thing as eternal life, of course.
“The risk of mortality is still greater than zero,” she explains. “These individuals are equally subject to causes of death such as illness and accidents. There may also be other dynamics at play.”
In addition, there are records that supercentennial tortoises (ages that could exceed 150 years) can develop problems typical of human old age, such as cataracts in the eyes and heart disease. For now, the mystery of what happens in their bodies remains.
