It takes a finely tuned ear to describe the characteristics of a frog’s call—is it chirping, trilling, or is that more of a chucking sound? Each frog’s call is unique to its species, and by studying these animals, scientists like herpetologist David Blackburn are finding new evidence about how Africa itself has evolved. Highly sensitive to their surroundings, frogs can be very particular about the places where they live, and probably have been for 250 million years. When a frog’s habitat changes, it often must shift to a more suitable area if it is to survive, so studying the modern-day distribution of frog species helps reveal the history of the landscapes in which they live.
In 2011, Blackburn was part of a small team which mounted an expedition to Burundi, a small but densely populated country which borders the vast Congo River Basin, the Great Rift Valley, and Lake Tanganyika—an intriguing geographic crossroads for biologists. Their objective: to seek out the long-lost Bururi long-fingered frog (Cardioglossa cyaneospila) which hadn’t been seen there by scientists since 1949, during surveys conducted while the nation was under Belgian administration.
Since then, the country has seen political unrest, population growth, and habitat loss, so the research team was pleasantly surprised to find the habitats of the Bururi Forest Reserve were still relatively intact when they arrived. Blackburn had a hunch that the Bururi long-fingered frog’s call would sound similar to that of its suspected relatives in Cameroon, more than 1,400 miles away. Sure enough, on the fifth night he found one on a log by following the sound of its call.
Scientists believe that many of the species in Burundi’s high-elevation forests may be closely related to plants and animals found in Cameroon’s mountains, suggesting that at some point in the past, a cooler climate may have allowed the forests to become contiguous between them. The lone long-fingered frog specimen collected, which now resides in the Academy’s herpetology collection, can now be used for DNA studies to estimate how long the Cardioglossa species from Burundi and Cameroon have been genetically isolated from one another. The results will shed light on Africa’s historical climate conditions, a topic that has far-reaching implications for understanding the evolution of life in the continent that gave rise to our own species. Events that impacted frog evolution, like a wet or arid period a million years ago, would also have affected human ancestors.