SRA

Leaf-cutting ants are dominant herbivores in the Neotropical region. They are important ecosystem engineers and many species are agricultural pests of great ecological and economic importance. Leaf-cutting ants in the genus Atta Fabricius are widely distributed throughout the Americas. Phylogenetic relationships within the genus remain uncertain, and the delimitation and identification of some Atta species are problematic. Here, we address these uncertainties by employing phylogenomic markers (ultraconserved elements, hereafter UCEs) in an analysis that includes 2340 UCE loci from 224 Atta specimens from across the geographic distribution of the genus and 49 outgroup specimens. Our results inferred the monophyly of Atta and its 14 studied species (out of the 15 known and identifiable species) with high support, representing the most comprehensive phylogenetic estimate to date for this leaf-cutting ant genus. Within the genus Atta, we recovered four well-supported clades that coincide with the groups of species previously recovered and correlated with the prior described subgenera, Archeatta Goncalves, Atta s.s. Emery, Epiatta Borgmeier, and Neoatta Goncalves. Our use of the former subgeneric names here is entirely informal. Our analyses identified a series of major events in the Miocene, such as the origin of leaf-cutting ants 18.9 Million years ago (Ma), the divergence of Acromyrmex Mayr and Atta around 16.7 Ma, and crown-group origin of Atta around 8.5 Ma. Extant Atta species evolved very recently, originating in the late Pliocene and early Pleistocene, approximately 3.3 to 1.2 Ma (crown-group age). The Archeatta clade, occurring in North and Central America and the Caribbean, is the sister group of the remainder of all other Atta species, and its species retained the most plesiomorphic traits within the genus. The Atta s.s clade is composed of two species occupying North, Central, and South America. Species in the Epiatta clade, containing seven species, are entirely South American, and the two species of the Neoatta clade occur in Central and South America. The Neoatta clade includes the species Atta robusta Borgmeier, the species with the youngest crown-group age in the genus of 0.3 Ma. Our phylogeny provides the first evidence that Atta goiana Goncalves belongs to the Epiatta clade and indicates, for both the Epiatta and Neoatta clades, an interesting pattern in which closely related species exhibit distinct ecologies. The very young ages of the genus Atta and its component species indicate a recent, rapid radiation. Our biogeographic analyses suggest that the common ancestor of the genus Atta originated in North America and that a daughter lineage, which subsequently dispersed to South America, rapidly diversifying in the newly formed Cerrado biome