Fanged Frogs Evolve to Fill Island’s Ecological Niches

Brandon T. Bisceglia

Darwin’s finches may have some competition. A team led by Biologist Ben Evans at McMaster University report that they have found a group of frogs that evolved to fill a plethora of niches on the Indonesian Island of Sulawesi. The researchers discovered 13 species of frogs on the island, all belonging to the genus Limnonectes. Nine of the species had never before been described by scientists.

The frogs showed an unusual array of adaptations, living in both the wettest and driest parts of the island. Some species fertilized their eggs internally, while others did it externally. Some had webbed feet for life in swift-moving water, while others that lived on land had minimal webbing. Some were small, others large.

This discovery echoes one by Charles Darwin nearly two centuries ago. He realized that finch species across the Galapagos archipelago had adapted to the differences in their environments. It became one of the most famous illustrations of his theory of evolution.

“Darwin found that the finches had evolved changes to the shapes of their beaks, allowing them to access different food sources,” said Evans in a press release from McMaster. “With the frogs, we found that they have made a number of adaptations including in body size, amount of webbing in their feet and how they raise their young – all of which matched the demands of their particular ecological niches.”

The group of frogs is named for their “fangs,” pairs of bony protrusions that stick up from their lower jaws. They are not teeth, and scientists are not yet sure what they are used for. Evans and his team speculate in their paper that the diversity of fanged frogs on Sulawesi is due in part to a lack of competition for ecological slots. He notes for comparison that there are fewer species of Limnonectes in the Philippines, which should have the twin advantages of being much larger and being composed of numerous islands. However, another genus of frogs called Platymantis competes for space in the Philippines. That group is absent from Sulawesi.

In all, the researchers caught 683 frogs by hand. The team’s paper is titled “Adaptive Radiation and Ecological Opportunity in Sulawesi and Philippine Fanged Frog (Limnonectes) Communities.” It was published in the August issue of The American Naturalist.