Bergmann’s rule within physiological ecology postulates that animals get larger at higher latitudes and altitudes. Similarly, the temperature-size rule predicts that although animals grow more slowly at cold temperatures, they reach a larger adult size (but see Angiletta and Dunham 2003). A study published today in the Proceedings of the National Academy of Sciences takes these ideas one step further. Researchers have shown that temperature is also the predictor behind the observation that ectotherms, or cold-blooded animals, live longer at higher altitudes and latitudes.
Stephan Munch and graduate student Santiago Salinas, both of Stony Brook University, collected lifespan data for more than 90 animal species, from terrestrial, freshwater, and marine environments. They studied organisms with different average longevities–from copepods that live only 12 days to mussels that can live as long as 74 years. In particular, pearl mussels have astounding geographic variation in lifespan: In Spain, they live about 29 years, but at a higher latitude in Russia they can live up to 200 years.
The scientists found that the trajectory of changing lifespan with changing temperature closely mimicked that predicted by the metabolic theory of ecology, or MTE, which makes physiological predictions irrespective of body size. Said Salinas in a press release:
“You can think of an animal as a beaker in which chemical reactions are taking place. 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.”
Salinas made the compelling argument that this finding implies that small changes in temperature, such as those created by global warming, could be a big deal:
“It is interesting to consider how cold-blooded species are likely to react in the face of global warming. Because of the exponential relationship between temperature and lifespan, small changes in temperature could result in relatively large changes in lifespan. 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.”