Body temperature and life expectancy
Zoologists have found no differences in the average aging rate of cold-blooded and warm-blooded tetrapods
Sergey Kolenov, N+1
It is generally believed that cold-blooded animals age slower on average than warm-blooded ones. However, an analysis of the aging and life expectancy of 77 amphibian and reptile species has shown that this is not the case. Researchers have found that some of their species age more slowly and live longer than birds and mammals, while others — on the contrary. At the same time, turtles and hatterias turned out to be the record holders for longevity. As stated in the article for the magazine Science (Reinke et al., Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity), turtles age negligibly slowly. Perhaps it's all about their shell, which provides protection from predators and helps them live to an advanced age.
Among cold—blooded — more precisely, poikilothermic - animals there are many centenarians. For example, Galapagos turtles (Chelonoidis niger species complex) live on average for a hundred years, and Greenland polar sharks (Somniosus microcephalus) have a record of longevity among vertebrates — their average life expectancy is 272 years. At the same time, some fish, salamanders and turtles age negligibly slowly (negligible aging is called the rate of aging, which is difficult to statistically distinguish from zero, as well as zero correlation between age and the probability of death).
It is assumed that the high life expectancy of poikilothermic animals is associated with their relatively slow metabolism, the rate of which is further reduced in a cool climate. In addition, they grow all their lives, which means that natural selection should have eliminated from their genome most of the harmful mutations that manifest themselves at a late age. An additional factor providing poikilothermic animals with a long life may be various protective devices, such as turtle shells, crocodile osteoderms or venom of snakes and salamanders.
A team of zoologists led by Beth A. Reinke from Northeastern Illinois University decided to test these assumptions. To do this, they analyzed the literature data on how long representatives of 107 wild populations of reptiles and amphibians belonging to 77 species live. This information was collected by tagging and recapturing animals, and the research lasted from four to sixty years. For each population, Reinke and co-authors calculated the aging rate (derived from the mortality curve) and life expectancy (that is, the number of years after which 95 percent of adults in the sample die).
The researchers found that in every amphibian and reptile group included in the sample, there is at least one species with negligible aging. In this case, this means that mortality does not increase with age in such species and fertility does not decrease (the authors focus on two of the three Finch criteria; for comparison, the creators of the Anage database also take into account a number of physiological indicators of the body). The rate of aging of turtles was the slowest — an average of 0.04. At the same time, in 14 species of these reptiles included in the analysis, the aging rates were close, from -0.01 to 0.23. Hatteria age as slowly as turtles (their aging rate was 0.005). In crocodiles and salamanders, this process is faster (0.14 and 0.18, respectively), the aging rate of scaly reptiles, such as lizards and snakes, is 0.55, and tailless amphibians - 0.41.
The average life expectancy of turtles was 39 years, and hatteria — 137 years. In other reptiles and amphibians, these indicators were much more modest: 21 years in crocodiles, 12 years in scaly reptiles, ten years in salamanders and eight years in frogs.
Contrary to traditional beliefs, the authors found no evidence that poikilothermic tetrapods age slower on average and live longer than homoiothermic (warm-blooded) ones. Instead, it turned out that some amphibian and reptile species age more slowly and live longer compared to the average values for birds and mammals, while others, on the contrary, age faster and live less. A negative correlation between the rate of aging and life expectancy was found among both poikilothermic and homoiothermic animals.
Reinke and her colleagues also found that the rate of aging of cold-blooded animals depends on temperature. Reptiles age faster at high temperatures, and amphibians age slower. In addition, it turned out that amphibians and reptiles protected by a shell, osteoderms or poison age more slowly. Interestingly, species with carapace or osteoderms live longer than species with venom or devoid of protective devices.
At the last stage, the authors confirmed the existence of a relationship between the age of puberty and fertility on the one hand and the rate of aging and life expectancy on the other. It turned out that the earlier amphibians and reptiles begin to reproduce and the more offspring they bring, the faster they age. Previously, similar patterns were found in birds and mammals. At the same time, the rate of aging of amphibians is more influenced by fertility, and for reptiles, the age of the beginning of reproduction turned out to be more important. In addition, the later amphibians and reptiles begin to reproduce, the higher their life expectancy.
Thus, the most important factors affecting the aging rate and life expectancy of poikilothermic tetrapods are the ambient temperature, the presence of protective devices, the age of the beginning of reproduction and fertility. And the amazing longevity of turtles, apparently, is due to the fact that they have a shell that provides them with protection from predators.
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