UCE phylogenomics inform the systematics and geographic range evolution of the harvester ant genus Pogonomyrmex

The harvester ant genus Pogonomyrmex is common in arid regions of North America, South America, and Hispaniola. Here, we use ultraconserved elements (UCEs) to infer the most comprehensive phylogeny of the genus to date. Our inferred topology largely supports previously hypothesized Pogonomyrmex evolutionary relationships and species groups. Our divergence dating analysis substantially pushes back the age of both Pogonomyrmex and the Pogonomyrmecini tribe, suggesting an early Eocene origin for Pogonomyrmex. We infer that Pogonomyrmex likely originated within the Pacific dominion ecoregion of Northern South America. Pogonomyrmex (excluding the Pogonomyrmex mayri clade) likely adapted to cooler and drier climates in the middle Eocene. The genus spread to North America in the late Eocene, likely aided by the ephemeral volcanic islands of the Panama Arc. A smaller group of Pogonomyrmex dispersed to Mesoamerica and North America in the Oligocene and to Hispaniola in the Miocene, most likely out of Mesoamerica. Our results suggest that adaptations to arid environments allowed Pogonomyrmex to spread and diversify in regions of the Americas that were actively becoming cooler and drier due to orogeny and other geologic processes.