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Following up on last week's post on pearl mussel longevity and antioxidants (or not), here's more on the relationship between longevity and environmental temperature in cold-blooded species:
Munch and Salinas looked at lifespan data from laboratory and field observations for over 90 species from terrestrial, freshwater, and marine environments. They studied organisms with different average longevities - from the copepod Arcartia tonsa, which has an average lifespan of 11.6 days, to the pearl mussel Margaritifera margaritifera, which has an average lifespan of 74 years. They found that across this wide range of species, temperature was consistently exponentially related to lifespan.
The relationship between temperature and lifespan 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."
Scientists in the audience can find the paper at PNAS. The lesson proposed here, I think, is that the study of comparative longevity between species - largely undertaken to gain insight into aging in higher species, and partly in search of mechanisms that might one day be introduced into a re-engineered human metabolism - might benefit from skipping over cold-blooded animals. If the overwhelming majority of differences can be explained by temperature, then the odds of finding something interesting and new are far lower than for investigations of warm-blooded species.
Which is not to say that I think searching for ways to alter human biochemistry is a good way ahead. It'll happen, because a large research community is presently heading in that direction, but I don't see it being either (a) rapid, or (b) very helpful for those of us who will be old when results start to emerge. Slowing aging down doesn't do much for those who are already old.
 Munch, S., & Salinas, S. (2009). Latitudinal variation in lifespan within species is explained by the metabolic theory of ecology Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0900300106
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Posted by Reason
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