Physically fit frogs have faster-changing genomes, says a new study of poison frogs from Central and South America.

Stretches of DNA accumulate changes over time, but the rate at which those changes build up varies considerably between species, said author Juan C. Santos of the National Evolutionary Synthesis Center in Durham, North Carolina.

In the past, biologists trying to explain why some species have faster-changing genomes than others have focused on features such as body size, generation time, fecundity and lifespan. According to one theory, first proposed in the 1990s, species with higher resting metabolic rates are likely to accumulate DNA changes at a faster rate, especially among cold-blooded animals such as frogs, snakes, lizards and fishes. But subsequent studies failed to find support for the idea.

The problem with previous tests is that they based their measurements of metabolism on animals at rest, rather than during normal physical activity, Santos said.