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Endangered River Turtle’s Genes Reveal Ancient Influence of Maya Indians

August 17, 2011

A genetic study focusing on the Central American river turtle (Dermatemys mawii) recently turned up surprising results for scientists at the Smithsonian Conservation Biology Institute and collaborators involved in the conservation of this critically endangered species. Small tissue samples collected from 238 wild turtles at 15 different locations across their range in southern Mexico, Belize and Guatemala revealed an unexpected lack of genetic structure, the scientists wrote in a recent paper published online May 17, 2011 in the journal Conservation Genetics. The turtles, which are entirely aquatic, represent populations from three different river basins that are geographically isolated by significant distance and high mountain chains.

“We were expecting to find a different genetic lineage in each drainage basin,” said the paper’s main author, Gracia González-Porter of SCBI’s Center for Conservation and Evolutionary Genetics. “Instead, we found the mixing of lineages. It was all over the place.”

Despite appearing isolated, the genetic data showed the different turtle populations had been in close contact for years. But the researchers wondered how that was possible. The best possible explanation, González-Porter and her colleagues said, is that for centuries humans have been bringing them together. The turtles have been used as food, in trade and in rituals for millennia, widely transported and customarily kept in holding ponds until they were needed.

“For centuries, this species has been part of the diet of the Mayans and other indigenous people who lived in its historic distribution range,” the scientists said in the paper. “D. mawii was a very important source of animal protein for the ancient Mayans of the Peten (Preclassic period 800-400 B.C.) . . . And it is possible that these turtles were part of the diet of the Olmec culture more than 3,000 years ago.”

One specimen of the Central American river turtle was found in an ancient Teotihuacan burial site in Mexico, a spot located more than 186 miles from the known range of this turtle, the researchers said. An ancient sculpture of a Central American river turtle at the National Museum of Anthropology in Mexico City was found in the Basin of Mexico, more than 217 miles from the turtle’s range.

“The Central American River turtle is tame and resilient, which makes it easy to transport” González-Porter said. “Their shells give them lots of protection. People don’t have refrigeration so they put the turtles in ponds in their backyards.”

During the rainy season in the tropics, the water flows are huge, she said. Rivers and ponds flood, captive turtles escape and mix with the local turtles.

This ancient practice still persists today. In Guatemala, Central American river turtles are kept in medium-sized ponds where they can be easily captured when needed. Similarly, in the state of Tabasco, Mexico, captured turtles are kept in rustic ponds and raised until they are either consumed or sold.

The genetic analysis of the Central American river turtle was initiated because these animals are critically endangered. They are the last surviving species of the giant river turtles of the family Dermatemydidae. These animals are currently the most endangered turtle species in Central America. A recent increase in the commercial demand for its meat has pushed it to the brink of extinction—2.2 pounds of their meat can fetch $100. Most local populations have disappeared and the turtle is now largely restricted to remote areas that are inaccessible to humans.

The article, "Patterns of genetic diversity in the critically endangered Central American river turtle: human influence since the Mayan age?" was co-authored by:

The Smithsonian Conservation Biology Institute plays a key role in the Smithsonian’s global efforts to understand and conserve species and train future generations of conservationists. Headquartered in Front Royal, Va., SCBI facilitates and promotes research programs based at Front Royal, the National Zoo in Washington, D.C., and at field research stations and training sites worldwide.