Aging accelerates for frogs and toads in warmer climates, study finds

Frogs and toads live faster and die younger in warmer habitats, a new study has found. That adds to evidence that cold-blooded animals may face accelerated aging and a shortened lifespan as climate change heats up the Earth.

The study looked at populations of two species native to western Canada and the U.S., the Columbia spotted frog and the western toad, along with the European common frog and the common toad, also from Europe.

The researchers looked at the increase in mortality with age, known as "senescence." That measure is used as a way to capture all effects of aging, from slower reaction time that could make it easier to be captured by predators to increased susceptibility to disease.

They found that the rate of senescence in the four species increased as the mean average temperature increased.

"In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline," said the study published this week in Proceedings of the National Academy of Sciences.

Warmer temperatures speed up metabolism, the chemical processes that allow animals to use energy to do things such as move and grow. Warm-blooded animals like humans keep a stable body temperature and therefore a pretty stable metabolic rate. But for cold-blooded animals such as amphibians, reptiles, fish and insects, body temperature, metabolism and the animal's activity level are driven by the ambient temperature, said Hugo Cayuela, lead author of the study.

"And of course, senescence is influenced by metabolism and activity," said Cayuela, who started the project while at Laval University in Quebec City and is now a postdoctoral researcher at Université Claude Bernard in Lyon, France. 

That had been shown in lab studies of animals such as worms and fruit flies.

But there actually hadn't been much study of aging in amphibians, Cayuela said, beyond evidence that, like humans, they show age-related genetic damage in their cells as they get older.

Cayuela suspected he could probably learn something from data that had already been collected to monitor amphibian populations, which are declining worldwide.

Cayuela and his collaborators from institutions in Switzerland, France, Sweden, Finland, the U.S. and China analyzed data from populations of four species that had been monitored over 11 to 29 years. (Frogs and toads of those species typically have a lifespan of about a decade). 

Each year, researchers caught adult frogs and toads of those species at specific locations using nets or their hands and tagged them with microchips similar to the ones used to identify pet dogs and cats if they get lost. Multiple times a year, the researchers returned and recaptured as many individuals as they could, using the tags to identify them, since they tend not to travel very far. That allowed them to follow individuals as they aged and estimate mortality over time.

What they found is that senescence in all four species increased as the average annual temperature increased. In three out of the four, the median lifespan also decreased with increasing temperature. Cayuela said it wasn't clear why that wasn't the case for the fourth species, the Western toad.

With climate change, it's likely that water temperatures where these species live will increase over the next few decades.