Zero-speed aging
Captive turtles refused to grow old
Sergey Kolenov, N+1
A male giant turtle (Aldabrachelys gigantea) named Jonathan. Wikimedia Commons.
Zoologists have found out that the aging rate of many species of turtles when kept in captivity is zero. At the same time, for representatives of some species, the risk of death decreases with age. As noted in the article for the magazine Science (da Silva et al., Slow and negligible senescence among testudines challenges evolutionary theories of senescence), further studies of turtles will help refine evolutionary theories of aging.
Turtles can live a very long life. For example, a male giant turtle (Aldabrachelys gigantea) named Jonathan, who now lives on the island of St. Helena in the Atlantic Ocean, has reached the venerable age of 190 years. And a female Galapagos tortoise (Chelonoidis niger species complex) named Harriet was at least 176 years old at the time of her death in 2006. Scientists suggest that at least two species of turtles age negligibly slowly — that is, the rate of their aging is difficult to statistically distinguish from zero, and the correlation between age and the probability of death is zero.
A team of zoologists led by Fernando Colchero from the Species360 conservation organization decided to learn more about how turtles manage to live for so long. To do this, the researchers collected information about the captivity of 52 species of turtles, differing in body weight, life expectancy and features of life cycles. For females of 47 species and males of 39 species, they estimated the age structure of mortality, life expectancy and the rate of aging.
Based on these data, the authors calculated the rate of aging at the age when the survival function reaches 0.2 (that is, by the age when 80 percent of adults have time to die). It turned out that for females of 35 species and males of 31 species of turtles (74.5 percent and 79.5 percent, respectively), the aging rate at this age is zero. Females of two species and males of one species, including Mediterranean (Testudo graeca) and black freshwater turtles (Siebenrockiella crassicollis), demonstrated a negative aging rate. In several other species, including gigantic ones, the aging rate turned out to be close to zero.
Kolchero and his colleagues believe that zero, negative and near-zero aging rates may indicate negligible aging in most turtle species (it should be noted that the authors focus only on one of Finch's criteria and do not take into account fertility and a number of physiological indicators of the body). Nevertheless, in females of ten species and males of seven species of turtles, the aging rate was positive. This indicates that their risk of death increases with age even in captivity, where they are protected from predators and receive food and treatment. At the same time, in females of 37 species and males of 34 species of turtles, the aging rate was lower than in modern humans, and also significantly lower than in most mammals.
As the authors suggested, life expectancy in adulthood for both sexes of turtles positively correlates with their body weight. Males of species with reverse sexual dimorphism, in which females are larger than males, tend to live longer than males of species in which males are larger than females. This is probably due to the fact that with reverse sexual dimorphism, males are less aggressive towards each other, which reduces the risk of death during conflicts over partners. Calculations also showed that male turtles live on average 20 percent longer than females. However, the researchers could not find any differences in the rate of aging between the sexes.
In their work, Kolchero and co-authors used data on turtles that are kept in captivity. To test whether the results obtained can be transferred to wild populations of these reptiles, the researchers compared the life expectancy and aging rate in captivity and in the wild for three species of turtles: painted (Chrysemys picta) and red-eared (Trachemys scripta), as well as forest kinix (Kinixys homeana). It turned out that the last two species in nature age several times faster than in captivity. Painted turtles from wild populations, on the contrary, age a little slower than relatives from zoos and nurseries.
According to a recent study, the rate of aging of humans and other primates is unchanged, and the increase in human life expectancy, which was observed throughout the XX century, is due to the fact that they die later, But in captive turtles, the rate of aging can reach zero or even become negative. The authors hope that further studies of these reptiles will help refine existing evolutionary theories of aging, which have mainly been tested on mammals and birds.
One of the reasons for the amazing longevity of turtles may be the presence of a protective shell. Zoologists came to this conclusion after analyzing the aging rate and life expectancy of 77 species of amphibians and reptiles. In addition, the researchers found that, contrary to popular belief, cold-blooded animals on average age no slower than warm-blooded ones.
Portal "Eternal youth" http://vechnayamolodost.ru