Army ant invasions reveal phylogeographic processes across the Isthmus of Panama.

Female army ants cannot fly, making them very poor dispersers across water barriers. This dependence on terrestrial corridors motivated the investigation by Winston et al. (), published in this issue of Molecular Ecology, into the role of Panamanian isthmus formation in the diversification of Eciton army ants. Complete closure of this isthmus occurred around three million years ago (3 Ma), but it has also been hypothesized that earlier, temporary land connections facilitated additional colonization events between South and Central America over the past 13 million years or more. The phylogenomic and population genomic analyses by Winston et al. () uncovered multiple incursions of Eciton lineages into Central America between 4 and 7 Ma. Their study contributes to a growing body of evidence arguing that transitory land bridges predating 3 Ma supported substantial intercontinental biotic exchange.