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Follow the Ants

A population genetics study of ants has led scientists to reconsider when North and South America were joined by the Isthmus of Panama, Nature News reports.

The Field Museum's Corrie Moreau and her colleagues genotyped ants belonging to nine Eciton ant species to determine their phylogeny, as they recently reported in Molecular Ecology. The researchers' analyses suggested that Central American Eciton lineages diverged from their sister South American lineages between four million and seven million years ago. As Eciton species only move on dry land, this indicates that the Isthmus of Panama may have been formed earlier than previous estimates of three 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," Moreau tells Nature News. She notes that some geological studies have also suggested an earlier formation of the isthmus.

But Nature News adds that not all geologists are convinced. The Smithsonian Tropical Research Institute's Anthony Coates points out that multiple lines of evidence support the three million year estimate of the isthmus' age. In addition, a sister ant species was able to raft to the Caribbean, something that Eciton might have been able to do as well, if the distance was small, Nature News adds.