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Abstract The New World army ants (Hymenoptera: Formicidae) comprise the 5 genera of the Eciton species group, and together they are important keystone predators in tropical and subtropical environments. Generic boundaries in the group have been considered solid and stable for nearly 100 years. Workers of the widespread and diverse genus Neivamyrmex are readily separable from the other 4 genera by lacking a subapical tooth on the tarsal claw, while males can be separated with genitalic characters. The genus Labidus is also widespread and is often abundant, with several species that are conspicuous surface foragers. The least known species of Labidus is L. mars, the workers of which have the tarsal tooth but otherwise share many traits with some Neivamyrmex, being completely eyeless and subterranean. This led us to question its generic placement. Here, we used ultraconserved element (UCE) phylogenomics to show that Labidus mars belongs to the genus Neivamyrmex. All phylogenies, inferred using multiple partitioning schemes and a species tree analysis, recovered the same topology, placing Labidus mars workers within Neivamyrmex. Sequenced males of L. mars were found to be within Labidus and thus incorrectly associated with L. mars. Based on these results and review of key specimens, including types, the following taxonomic changes are made: Neivamyrmex mars (Forel 1912) is a new combination; Labidus nero (Santschi 1930) (rev. stat.) is a male-based taxon revived from synonymy under L. mars; and L. denticulatus (Borgmeier 1955) (new stat.), a male-based taxon and former subspecies of L. mars, is raised to species. 

Obligatory ant–plant symbioses often appear to be single evolutionary shifts within particular ant lineages; however, convergence can be revealed once natural history observations are complemented with molecular phylogenetics. Here, we describe a remarkable example of convergent evolution in an ant–plant symbiotic system. Exclusively arboreal,Myrmelachistaspecies can be generalized opportunists nesting in several plant species or obligately symbiotic, live-stem nesters of a narrow set of plant species. Instances of specialization withinMyrmelachistaare known from northern South America and throughout Middle America. In Middle America, a diverse radiation of specialists occupies understory treelets of lowland rainforests. The morphological and behavioural uniformity of specialists suggests that they form a monophyletic assemblage, diversifying after a single origin of specialization. Using ultraconserved element phylogenomics and ancestral state reconstructions, we show that shifts from opportunistic to obligately symbiotic evolved independently in South and Middle America. Furthermore, our analyses support a remarkable case of convergence within the Middle American radiation, with two independently evolved specialist clades, arising nearly simultaneously from putative opportunistic ancestors during the late Pliocene. This repeated evolution of a complex phenotype suggests similar mechanisms behind trait shifts from opportunists to specialists, generating further questions about the selective forces driving specialization. 

Abstract The classification of ants (Hymenoptera: Formicidae) has progressed in waves since the first 17 species were described by Linnaeus in the 1758 edition of Systema Naturae. Since then, over 18,000 species-rank names have accumulated for the global myrmecofauna, of which ~14,260 living and ~810 fossil species are valid. Here, we provide a synopsis of ant biodiversity and review the history and classification of the family, while highlighting the massive growth of the field in the new millennium. We observe that major transformation has occurred for ant classification due to advances in DNA sequencing technologies, model-based hypothesis testing, and imaging technologies. We therefore provide a revised and illustrated list of diagnostic character states for the higher clades of Formicidae, recognizing that vastly more work is to be done. To facilitate discussion and the systematic accumulation of evolutionary knowledge for the early evolution of the ants, we suggest an informal nomenclatural system for the higher clades of ants, based on names currently in use and a set of names that have been democratically selected by the authors. To guide future work on ant systematics, we summarize currently available databases and present perspectives on regions in need of biodiversity exploration, challenges facing the field, and the future of ant taxonomy.