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.
Why study aging amphibians?
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.
What this means for climate change impacts on frogs and toads
With climate change, it’s likely that water temperatures where these species live will increase over the next few decades.
“Senescence will accelerate and lifespan will be shortened,” Cayuela said. “I think that’s the prediction that we can likely make.”
His paper suggests this likely applies not just to frogs and toads, but cold-blooded animals in general.
While individuals may be able to compensate by breeding earlier, Cayuela said that in many cold-blooded animals, the older individuals are bigger and contribute more to reproduction. Faster aging and shorter life spans may therefore have a negative impact on the entire population.
“It will be difficult to mitigate the effects of climate change on the demography of amphibians,” he added.
“But what you can do is reduce additional anthropogenic stresses like habitat loss.”
David Green is a biology professor at McGill University who has spent his whole career studying amphibians, including the impact of climate change on some Canadian species. He has collaborated with Cayuela before, but wasn’t involved in this particular study.
He was interested in the results. “It’s one of these great papers that confirms our suspicions, which is always reassuring,” he said.
It was known amphibians’ metabolisms should speed up in warmer surroundings. “This should make them live faster and die younger,” he said. “And lo and behold, it does.”
He said this could have negative impacts, as longer-lived species tend to be less vulnerable to poor environmental conditions in any given year compared to shorter-lived species. But frogs are generally long-lived, Green said.
“If they speed up and reproduce when they’re younger, it may not be so terrible.”
Stephen Lougheed, a conservation biology professor at Queen’s University, was also not involved in the study, but does research on how climate change is affecting organisms including amphibians. He said the fact that the researchers were able to detect the relationship between temperature and aging in wild populations is exciting.
“The implications, I think, are fairly profound because amphibians are one of the most threatened groups of terrestrial vertebrates in the world,” he said. This study is improving the understanding some of the factors that contribute to their decline, he added.
“And maybe that would allow us to make recommendations of how we might mitigate, accommodate or even reverse this.”