More young geckos have been found hiding in the limestone towers of Southeast Asia

Landscapes in Southeast Asia once thought to stifle biological evolution may instead fuel its fires.

Karst ecosystems have been referred to as arks of biodiversity, a term that highlights their biological richness but also implies that they merely preserve ancient lineages. These landscapes, with their isolated caves, cliffs and burrows, were thought to shelter species from extinction without contributing much to evolution.

But the discovery over the past few years of nearly 200 species of geckos in such regions reveals that the karsts are far from stagnant. “They’re not museums, they’re species centers,” says evolutionary biologist Lee Grismer of La Sierra University in Riverside, California.

When Grismer first explored the karst landscapes of Myanmar in 2017, the wealth of life hidden within the limestone towers and caves left him amazed. During a 19-day expedition, these ancient rock formations, rising abruptly from the surrounding farmland, revealed geckos so distinctive and unexpected that his team identified 12 new species.

Since then, Grismer and his colleagues have entered similar formations across Southeast Asia, delving into the evolutionary secrets they hold. In early 2024, an expedition to western Cambodia discovered three new species of bow-toed gecko and a slender gecko—all detailed in forthcoming papers—bringing the number of gecko species he has described to about 185. “The biodiversity in these landscapes is just off the charts,” says Grismer.

The discoveries of geckos highlight this dynamism. Many karst-dwelling geckos belong Cyrtodactylusthe third largest genus of vertebrates in the world with nearly 400 species described so far. The geckos of this genus discovered by Grismer and his team are among the most recently evolved members of their groups. They exhibit unique adaptations, such as elongated limbs, larger eyes, and flatter heads, that enable them to cling to rock faces, much like expert climbers.

Grismer compares karst formations to islands in an archipelago. Each formation, he says, serves as an evolutionary microcosm, producing species completely different from neighboring karsts. “Species come from completely different species groups and different periods in history.”

The true extent of gecko diversity in the karsts remains unknown. Grismer and his colleagues have only surveyed about 20 percent of the formations in western Cambodia, and he plans to return there and to Myanmar in 2025. “It wouldn’t surprise me if there are another 200 species there.”