Researchers find that havens for biodiversity near the equator may owe their existence to the tropical climate.

It’s not the palm trees and lush terrain that have lured so many different species to habitats along the Earth’s equator—it’s the temperature.

According to a study slated for publication in the June 13th issue of Proceedings of the National Academies of Sciences, the immense biodiversity in the world’s tropical habitats could be a result of high environmental temperatures, which speed evolutionary change.

A research team led by biologist Andrew Allen of the National Center for Ecological Analysis and Synthesis created a model to quantify the effects of temperature on genetic evolution. In devising the algorithm, the group assumed that metabolism—the rate at which an organism transforms energy—influences the rate of genetic change.

For cold-blooded animals especially, environmental temperature plays a big role in regulating metabolism. Thus, by the researchers’ model, high temperatures found along the equator can speed up the metabolisms of certain organisms that live there, thus fostering faster genetic change and, eventually, the evolution of new species.

“If you speed up the rate at which organisms transform energy, they reproduce more quickly and they die younger,” Allen said. “DNA gets replicated more quickly because reproduction happens more quickly.”

Furthermore, Allen said, it’s possible that organisms with faster metabolisms accrue genetic mutations more quickly because their bodies generate more free radicals, unstable chemical elements or compounds that have one unpaired electron, which are thought to induce mutations.

Allen’s model predicted that the rate of genetic variation in a certain type of plankton is 15 times faster when it lives near the equator than when it lives in the Arctic. Data spanning 30 million years of the plankton fossil record supported the model’s predictions, according to Allen.

The research group also found that the amount of energy needed to create a new species is fixed—as well as enormous. It takes 1023 joules of energy—more than the entire world consumes via fossil fuels in a year—to create just one new species of plankton, Allen said.

“It’s a huge number,” he said. “But when you think about how many generations and millions of years it really takes for a species to evolve, it makes sense.”

Kaustuv Roy, a biologist at the University of California, San Diego agreed that the idea of environmental temperature driving speciation was interesting, but he suggested this relationship may be too simple. 

“Whether temperature’s the only cause of the global distribution that we see remains to be seen,” Roy said.

Indeed, factors beyond environmental temperature are likely to also contribute to rates of speciation, said Allen, especially for warm-blooded animals, which can internally regulate their own temperatures.

Originally published June 8, 2006

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