Tropical frogs can adapt to climate change, but rapid warming still a huge threat

Sooglossus frog - Sooglossus sechellensis from the island of Praslin. Credit: Ji
Sooglossus frog - Sooglossus sechellensis from the island of Praslin. Credit: Jim Labisko

A population of Seychelles frog have adapted to a warmer climate over time, but as these adaptations have evolved gradually, the rapidly warming climate still poses a threat to species’ survival, according to a new study led by a UCL researcher.

In the study published in Global Change Biology , the researchers report that a subgroup of the Seychelles frog (Sooglossus sechellensis) adapted to historic sea level rise after finding themselves on an island with a different climate.

The frog is endemic to the islands of Mahé, Silhouette and Praslin in the Seychelles. The researchers focused on a population of Sooglossus sechellensis which were been forced to inhabit the significantly warmer island of Praslin.

Along with a warmer temperature, Praslin also lacks the high-elevation mist forest habitat that Sooglossus sechellensis inhabits on Mahé and Silhouette. With the population on Praslin having little to no opportunity to avoid the hotter climates, the researchers hypothesised that the population of frogs on Praslin must have adapted to survive in warmer environments than their closest living relatives and ancestors.

Co-author Dr Jeff Streicher (Natural History Museum) said: "Tropical amphibians exemplify the situation that faces a whole range of species due to human-induced climate change.

"We wanted to know how and if this isolated population of frogs had adapted to a warmer climate, to try and understand how organisms will cope as the climate becomes hotter."

Tropical amphibians, particularly those that inhabit islands, are vulnerable to a warming climate due to a range of factors - they are ectothermic (their body temperature is regulated by the external environment), prone to desiccation and are often restricted to very specific areas.

Using a wide range of data that included body size, bioacoustic data and elevational distribution, the researchers were able to show that some tropical amphibians have survived episodes of historic warming and therefore may have the capacity to adapt to the currently warming climate. For example, the frogs on Praslin were living at a lower, and therefore warmer elevation, than their closest living relatives on other islands. They also had the same activity patterns as their other island counterparts despite the warmer temperatures.

Lead author Dr Jim Labisko (UCL Centre for Biodiversity & Environment Research) said: "There were no apparent differences between the timings of daily vocal activity of the frogs on any of the islands, which was particularly interesting.

"On the islands of Mahé and Silhouette, different sooglossid species are each active at different times of day but there is only one species of sooglossid on Praslin, so no related competitors, and so we might have expected the Praslin frogs to shift their activity pattern to cope with the warmer temperatures and be more active at cooler periods, such as at night. However, this wasn’t the case and the frogs maintained the timing of their vocal activity, even at a warmer temperature."

Despite these adaptations, the researchers, including scientists from the Seychelles Islands Foundation and Perth Zoo, warn that local extinction is still a likely outcome for tropical frogs in a rapidly warming world. The frogs on Mahé and Silhouette (the closest living relatives of the frogs on Praslin) diverged from the frogs on Praslin around 8 million years ago. Therefore, the adaptions to a warmer climate seen in the frogs on Praslin may have occurred very gradually. Genetic evidence and differences in call characters from the study also suggests that the frogs on Praslin may have even evolved into a new species.

Dr Streicher said: "This population of frogs appear to have been able to adapt to a warming climate, even if this level of adaptation may have taken a long time. It’s exciting to think that this adaptive potential could also be present in other populations of climate-vulnerable organisms."

Dr Labisko said: "With a rapidly warming climate, it’s really important to understand how different species respond to climate change.

"Our study provides evidence that vulnerable species (even little brown island frogs!) can adapt to warmer climates, but they may only be able to do so when warming is gradual and natural selection can occur over millions of years. That makes the current climate crisis a major concern as most species will not have millions of years to adapt to rapidly rising temperatures."