DNA isolated from 1,600-year-old fossilized stools suggests migration from the Andes.
The answer to a Caribbean mystery could lie in fossilized faeces. An analysis of the microbial and plant DNA contained in a set of these fossils, or coprolites, sheds light on the origins of two ancient indigenous peoples who inhabited the islands of Puerto Rico before Christopher Columbus arrived in 1493. Microbial clues bolster the theory that the cultures had different origins and maintained distinct customs while sharing the island for hundreds of years.
Archaeologists have long suspected that two cultures called the Saladoids and the Huecoids had colonized Vieques, a small island just east of Puerto Rico’s largest island. It has been unclear, however, whether these populations were related or shared a common origin. Because of their distinctive style of pottery, the Saladoids are thought to have come from Venezuela, whereas the Huecoids may have come from the Andes of Bolivia. But experts based this supposition largely on differences in the styles of craftsmanship between the two peoples, including the discovery of carved Andean condors — which have a distinctive head crest — that have been found in Puerto Rico.
Researchers wanted a way to tell a more complete story. Both cultures left coprolites, so microbiologists Jessica Rivera-Perez of the University of Puerto Rico in Rio Piedras and Raul Cano of the California Polytechnic State University, San Luis Obispo, and their colleagues decided to inspect them for clues. They collected 10 samples of coprolite ranging in age from 1,000 to 1,600 years old, and extracted DNA. Using sensitive genetic-sequencing techniques, they were able to identify numerous bacterial, fungal and plant species.
Researchers extracted DNA from 10 coprolite samples, which ranged in age from 1,000 to 1,600 years old.
After analysing about 3.4 million DNA fragments, the researchers uncovered several dietary differences between the two peoples. The Huecoids’ stools contained DNA from maize (corn; Zea mays), which grows in the Andes, as well as from the yeast Saccharomyces. The traditional Bolivian fermented drink chicha includes yeast and maize. The Saladoid faeces contained no maize DNA. Rivera-Perez says that it had been unclear how maize first got to Puerto Rico; the fossil findings suggest that the Huecoids may have brought it with them.
And whereas the Saladoids’ stools contained a parasite that infects fish, those of the Huecoids contained one that infects marine invertebrates, highlighting another possible distinction between the two cultures.
When the researchers compared the bacteria in both populations’ coprolites with the stools of modern indigenous tribes in the Amazon, they found that the modern stools had very different microbial compositions. Rivera-Perez says that this could reflect differences in ancient and modern environments’ as well as how well organisms were preserved in the coprolites. The researchers will present their results at the American Society for Microbiology meeting in Boston, Massachusetts, next week.
Anthropologist Christina Warinner of the University of Oklahoma in Norman says that she is excited by the study because well-preserved DNA samples from the region are rare; DNA often degrades in the hot and humid climate of the Caribbean. Ancient DNA could be of further help in teasing apart the mystery of how the Caribbean was peopled, she says. She is currently studying the microbes and viruses preserved in ancient Mexican coprolites and tooth tartar in an attempt to understand how epidemics swept through the New World and decimated the native peoples.
Rivera-Perez says that the group next wants to start looking at specific genes in the microbes they found, such as those that help facilitate antibiotic resistance. Advances in DNA-sequencing technology, she adds, will allow researchers to extract even more information from the rare preserved samples. ”You can basically see what’s in there and start playing,” she says.