(ORDO NEWS) — A new published and incredibly thorough study of ectothermic tetrapods – reptiles and amphibians – provides experts with new insights into why cold-blooded animals have such long lifespans relative to their size.
This is the most comprehensive study of longevity and aging ever published: 114 different scientists studied 107 different wild populations spanning 77 different species.
Decades of data on how animals thermoregulate, environmental temperature, distinctive features and pace of life were collected and analyzed.
Of the 30 known species of vertebrates that can live up to 100 years, 26 are ectotherms, so the scientists wanted to find out how these animals manage to avoid inevitable death for so long.
The study uncovered many findings, including a link between species-protective physical or chemical traits – such as tough armor, spikes, carapace, or a venomous bite – and slowing down aging. Species-protective physical traits have also been associated with longer lifespans.
Technically these traits are known as protective phenotypes and they can be of great importance.
“These various defense mechanisms can reduce animal mortality over several generations,” says evolutionary biologist Beth Reinke of Northeastern Illinois University. “Thus, they are more likely to live longer, and this could change the intergenerational selection landscape in favor of a slower aging evolution.”
“It sounds dramatic to say that some species don’t age at all, but in fact their likelihood of dying doesn’t change with age once they stop reproducing.”
If an animal has a one in 100 chance of dying at age 10 and a one in 100 chance of dying at age 90, then it is negligible aging.
For the average US woman, by contrast, the odds are one in 2,500 at age 20 and one in 24 at age 80.
Slight aging has been observed in at least one species in each group of ectotherms, including frogs, salamanders, lizards, crocodiles, and turtles.
However, the study did not confirm another hypothesis: dependence on external temperatures to maintain body temperature (as cold-blooded animals do) and the associated lower metabolism is not a guarantee of long life.
The team found that ectotherms can live much longer or much shorter lives compared to similarly sized endotherms (warm-blooded animals).
This variation in aging rates and lifespan was much greater than in birds and mammals. The researchers isolated slow-aging wild tortoises: it was the only species in which a lower metabolism was associated with slower aging and lifespan, and it was the species with the strongest protective phenotype effect.
“It is possible that their altered, hard-shelled morphology provides protection and contributed to the evolution of their life histories, including little or no demographic aging and exceptional longevity,” says evolutionary biologist Ann Bronicowski of Michigan State University.
Comparative phylogenetic methods have been applied to these animals, which have been captured, tagged, released back into the wild and observed.
The research described in this paper may prove useful in the future in a variety of fields, whether it is studying the patterns of human aging or the work on the conservation of cold-blooded animals – and this is partly due to the breadth of coverage of time.
On top of that, there’s more to come: The team wants to study how soft-shelled and hard-shelled turtles differ in terms of aging, which may be enough to better understand why.
“Longitudinal studies are responsible for many of the scientific findings, such as monogamy and host-parasite relationships in sleepy lizards,” says ecologist Mike Gardner of Flinders University in Australia.
“These long-term datasets supporting animal longevity are also vital to reptile conservation efforts.”
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