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Photos of the skull and mandible of the Ctenomys lessai.

Ctenomys lessai (skulls and mandibles above) is one of the four newfound species of tuco-tucos. The four species evolved independently from each other.

Photograph by Scott L. Gardner, Manter Laboratory, University of Nebraska-Lincoln

Carson Vaughan

for National Geographic

Published July 17, 2014

Four new species of gopher-like rodents have been discovered in southern Bolivia.

Commonly called tuco-tucos, after the short "tuc tuc" sound of their vocalizations, Ctenomys are small, burrowing mammals. The four new species were found by Scott Gardner, curator at the University of Nebraska State Museum, and his research team after nearly three decades of sporadic fieldwork in the Andes and surrounding lowlands.

Tuco-tucos grow up to 12 inches (30 centimeters) long, weigh less than 1 pound (0.45 kilograms), and subsist on a diet of roots and vegetation. Scientists believe there are 38 to 60 species in South America, 12 of which have now been identified in Bolivia.

Gardner says the expedition team first located the new species in the early 1990s, with help from local farmers eager to rid their fields of the "pest." Gardner—who had recently finished his doctoral dissertation on every known species of Ctenomys—says he knew early on that they were dealing with previously undescribed animals.

Mitochondrial DNA sequencing confirmed the species' distinct genetic makeup. Not only did the tuco-tucos vary physically—in terms of color, skeletal characteristics, and other features—they varied chromosomally too.

Named in honor of different colleagues who contributed to the research, the four new species—Ctenomys erikacuellarae, Ctenomys yatesi, Ctenomys andersoni, and Ctenomys lessai—are described in a paper published last month by the Museum of Texas Tech University.

"In the current environment of human-caused environmental disturbance and degradation," says Gardner, "the discovery of four previously unknown species that are relatively large in size is phenomenal." And, he adds, yet another new species will likely be identified following further analysis of his team's data.

View of the dorsal, ventral, and lateral of the Ctenomys lessai.
Ctenomys are small, burrowing mammals (Ctenomys lessai skins shown above).
Photograph by Scott L. Gardner, Museum of Texas Tech University

A Fecund Spot

The discovery also testifies to the extreme biodiversity of southern Bolivia, "which has not been really appreciated until now," said Jorge Salazar-Bravo, a biology professor at Texas Tech and a co-author of the paper.

The complex topography of the Andes—specifically the central Andean backthrust belt—creates microclimates and ecological conditions that vary throughout the region. It also creates geographical barriers preventing the movement of certain organisms—and therefore the exchange of genetic information.

These conditions "may especially stimulate species diversification in subterranean rodents," Gardner and his colleagues write. It may also confirm that the central Andean backthrust belt should be considered what the scientists call a "speciation engine."

Evolution in Action

The paper—also co-authored by Joseph A. Cook, curator of mammals at the Museum of Southwestern Biology at the University of New Mexico—says tuco-tuco species likely originated after the rapid rise of the Andes.

As the mountains rose, they formed a series of deep, parallel valleys and ridges stretching north to south along Bolivia's eastern flank, dividing the original tuco-tuco population.

"What very likely happened is that some of these subpopulations started moving north in one valley, and other populations started moving up other valleys," Salazar-Bravo says. "And so that created the separation that was necessary for these populations to evolve independently from each other.

"Identifying these new species was total validation," he adds. "It's testing the theory of evolution over and over and over again."

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