Experts have a new understanding of why cold-blooded creatures typically have such lengthy lifespans in comparison to their size according to a recently published, exhaustive study of ectothermic tetrapods, or reptiles and amphibians.
With 114 separate researchers examining 107 distinct wild populations representing 77 different species, it is the largest study on lifespan and aging to have ever been published. Data on the way that animals regulate their body temperature, the temperature of their surroundings, unique traits, and rate of life have been collected and examined for decades.
Scientists were interested in learning how these creatures are able to evade the inevitable death for such a long time because 26 of the 30 known vertebrate species that may live above the age of 100 years are ectotherms.
The study produced a number of results, including a relationship between slower aging and physical or chemical characteristics that defend species, such as strong armor, spines, shells, or venomous bites. Longer lifespans were also associated with physical characteristics that safeguarded species.
These, which are formally referred to as protective phenotypes, are extremely important.
"These various protective mechanisms may reduce animals' mortality rates within generations," according to evolutionary biologist Beth Reinke, from Northeastern Illinois University. "Thus, they're more likely to live longer, and that can change the selection landscape across generations for the evolution of slower aging."
"It sounds dramatic to say that some species don't age at all, but basically their likelihood of dying does not change with age once they're past reproduction."
Negligible aging occurs when an animal has a one in 100 risk of dying at age 10 and a one in 100 chance of dying at age 90.
At least one species from each group of ectotherms, including frogs, salamanders, lizards, crocodilians, and turtles, showed little aging.
A contrary conclusion from the research, however, was not supported: having a lower metabolism and relying on ambient temperatures to regulate body temperature, as do cold-blooded species, was not a guarantee of long life. According to the research, ectotherms can live significantly longer or significantly shorter lives than endotherms of same size (warm-blooded animals).
Compared to birds and mammals, there was a significant difference in aging rates and longevity. The slow-aging wild turtles were selected out by the researchers because they were the only species examined in which a lower metabolism was connected to slower aging and a longer lifespan, and because they were the species in which the protective phenotypic impact was largest.
"It could be that their altered morphology with hard shells provides protection and has contributed to the evolution of their life histories, including negligible aging – or lack of demographic aging – and exceptional longevity," explains evolutionary biologist Anne Bronikowski from Michigan State University.
Data from animals that had been caught, tagged, released back into the wild, and observed were used in comparison phylogenetic approaches.
The research described in this study is likely to be helpful in the future in a variety of ways, including looking at human aging patterns or working on cold-blooded animal conservation efforts. This is partially because of the length of time the research spans.
The team aims to investigate how soft shell turtles and hard shell turtles age differently, which may be sufficient to more precisely pinpoint the causes behind it. There is also a lot more to look into as a result of the study.
"Longitudinal research is responsible for many research findings, such as the monogamy and host-parasite relations in sleepy lizards," claims ecologist Mike Gardner of Flinders University in Australia.
"These long-term datasets underpinning animal lifespans are also vital for reptile conservation efforts."
The research has been published in Science.
