Researchers Show Warmer Environment Means Shorter Lives for Cold-Blooded Animals
Temperature explains much of why cold-blooded organisms such as fish, amphibians, crustaceans, and lizards live longer at higher latitudes than at lower latitudes, according to research published at the end of July in the Proceedings of the National Academy of Sciences (PNAS) online. Assistant Professor Stephan Munch and Ph.D. candidate Santiago Salinas, both from the School of Marine and Atmospheric Sciences (SoMAS), found that for a diverse range of species whose body temperatures vary with the temperature of their surroundings, ambient temperature is the dominant factor controlling geographic variation of life span within species.
“We were intrigued by the fact that pearl mussels in Spain have a maximum lifespan of 29 years, while in Russia, individuals of the same species live nearly 200 years,” said Munch. “We wondered how a relatively small difference in latitude (Spain 43ºN and Russia 66ºN) could have such a drastic impact on life span. While one might expect that local adaptations or geographic variations in predator and food abundance would account for this disparity, we wanted to see whether the geographical variation in life span that we see in all sorts of species has a common physiological basis in temperature.”
Munch and Salinas looked at life span data from laboratory and field observations for more than 90 species. They studied organisms with different average longevities and found that across this wide range of species, temperature was consistently exponentially related to life span.
The relationship between temperature and life span that Munch and Salinas found through data analysis was strikingly similar to the relationship that the metabolic theory of ecology (MTE) predicts. The MTE is a modeling framework that has been used to explain the way in which life history, population dynamics, geographic patterns, and other ecological processes scale with an animal’s body size and temperature.
“You can think of an animal as a beaker in which chemical reactions are taking place,” said Salinas. “The same rules that apply to a liquid inside a beaker should apply to animals. Chemists have a relationship for how an increase in temperature will speed up reaction rates, so the MTE borrows that relationship and applies it, with some obvious caveats, to living things.”
The life span in 87 percent of the free-living species Munch and Salinas studied varied as predicted by the MTE. Yet after removing the effect of temperature, there was still considerable variation in life span within species, indicating that other, local factors still play a role in determining life span.
“It is interesting to consider how cold-blooded species are likely to react in the face of global warming,” said Salinas. “Because of the exponential relationship between temperature and life span, small changes in temperature could result in relatively large changes in life span. We could see changes to ecosystem structure and stability if cold-blooded species change their life histories to accommodate warmer temperatures but warm-blooded species do not.”