Ant genomes rewrite history of Panama land bridge

Colliding tectonic plates pushed up a strip of land from the watery abyss that once divided North and South America, forming the isthmus of Panama. But a study now hints that this happened millions of years earlier than scientists had thought.
               

Evolutionary and population-genetics data from Eciton army ants, which can only travel on dry ground, suggest that the isthmus formed 4–8 million years ago. The research, published on 25 October in Molecular Ecology1, challenges the long-held idea that the link between continents emerged no more than 3 million years ago.

“Our genomic data is very strong evidence that the army ants crossed this region much earlier in time than the model of the simple closure of the isthmus suggests,” says Corrie Moreau, associate curator at the Field Museum in Chicago, Illinois, and co-author of the study. She notes that recent geological studies have also hinted that the isthmus may have emerged earlier than 3 million years ago.

Genetics and geology collide

Moreau and her colleagues used a technique called genotyping to sequence small fragments of DNA from the genomes of multiple individuals from all nine Eciton species, which are found from Brazil to southern Mexico. This allowed the researchers to compare genetic variations both between species and within different individuals of the same species.

Anthony Coates, a geologist at the Smithsonian Tropical Research Institute in Panama City, is sceptical of any evidence contradicting the isthmus’s 3-million-year age. “There are still a series of investigations in different disciplines that all converge on the same number of around three million years ago. This is extremely rigorous evidence,” Coates says.

The geological battle lines, it seems, have been drawn. Whether they can form an ideological land bridge similar to the physical one that researchers are studying remains to be seen.