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Cold-blooded critters in hot water: Could global warming shorten the life spans of some animals?

Spanish pearl mussels don’t usually make it into their 30s. The same species bathing in Russia, however, can live for nearly 200 years.

The secret to the Russian pearls’ longevity may be slowly undermined if Earth’s seas continue to warm, because cooler waters supply the fountain of mussel youth, according to a study published today in the Proceedings of the National Academy of Sciences.

“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,” study co-author Stephan Munch of Stony Brook University in Long Island, N.Y., said in a statement. Alternatively, one might expect local adaptations or geographic variations in predator and food abundance to account for disparities in longevity.

Indeed, ambient temperatures were found to be exponentially related to life span in 87 percent of the more than 90 cold-blooded species studied—some in the wild, others in the lab. (The latter experiments could address the effects of varying temperatures without confounding habitat differences.) Munch and his student, Santiago Salinas, selected the animals from a range of environments, latitudes and average life spans, and controlled for body size in their analyses.

“You can think of an animal as a beaker in which chemical reactions are taking place,” Salinas said in a statement. “The same rules that apply to a liquid inside a beaker should apply to animals.”

Chemists know a rise in temperature will increase reaction rates; he suggests the same may be true of living things.

“This is really strong support for a fundamental prediction from the metabolic theory of ecology,” says James H. Brown of the University of New Mexico, who served as an editor on the paper and co-authored a seminal 2004 study on MTE theory, which suggests a mathematical relationship between body size, body temperature and metabolic rate. “The basic theory says that metabolic rates are higher on a per gram basis in smaller organisms and at higher temperatures,” says Brown. “So when it’s hotter, biological rates should go faster and biological times, like life span, should go shorter.”

MTE theory has been in hot water recently, with some ecologists suggesting it glosses over too many details. “Their argument would be that it is misleading to use a model that is as simple as ours,” says Brown. “They would argue that organisms have mechanisms to ameliorate some of the temperature differences.” 

Munch and Salinas note that temperature alone didn’t explain all the variability in their study—other local factors, such as predation, likely played a role. But they warn that their results might still be chilling news for cold-blooded critters. Based on current climate predictions, the researchers estimate these animals’ lives could shorten by as much as 42 percent in the next century using the MTE model.

“Small changes in temperature could result in relatively large changes in life span,” said Salinas, adding that these repercussions could extend to “changes to ecosystem structure and stability.” 

Photo of cold-blooed alligator and turtles by SteveByland via iStockPhoto

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