Uncovering parallel biogeography using phylogenomics in a widespread army ant genus

The genus Labidus is a clade of New World army ants (Hymenoptera: Formicidae) that are keystone predators in tropical and subtropical environments. Current taxonomy recognizes three worker-based species with broad geographic ranges, but each comprises multiple cryptic species with more restricted ranges. We reconstructed the phylogeny for Labidus using ultraconserved elements. We used these to inform the historical biogeography of this genus to reveal a pattern of parallel biogeography among its two most widespread worker-based clades. In both the Labidus coecus and L. praedator clades, a geographically central clade composed of several cryptic species in Central and northern South America is sister to a clade of peripheral isolates: one in Central and northern South America, one in southern South America. Two hypotheses that could lead to this parallel biogeography are 1) Brown’s overlooked hypothesis of centrifugal speciation in which genetic novelty is generated at the denser center of the range, with newer lineages at the center and older taxa persisting only at the periphery of their previously more extensive and contiguous ranges, or 2) habitat specialization, in which speciation occurs across a seasonal/aseasonal ecotone, with the seasonally adapted taxon spreading into the subtropics. These results have implications for our understanding of speciation processes and biogeography in the Neotropics, including the effects of the closure of the Panamanian Isthmus on dispersal, and may apply to other examples of disjunct distributions between Central and southern South America.