The Phylogeny and Evolution of Ants

Originating most likely in the early Cretaceous, ants have diversified to become the world's most successful eusocial insects, occupying most terrestrial ecosystems and acquiring a global ecological footprint. Recent advances in our understanding of ant evolutionary history have been propelled by the use of molecular phylogenetic methods, in conjunction with a rich (and still growing) fossil record. Most extant ants belong to the formicoid clade, which contains ∼90% of described species and has produced the most socially advanced and dominant forms. The remaining ants are old lineages of predominantly cryptobiotic species whose relationships to one another and to the formicoids remain unclear. Rooting the ant tree is challenging because of ( a ) a long branch separating ants from their nearest outgroup, and ( b ) heterogeneity in evolutionary rates and base composition among ant lineages. These factors will need to be given careful consideration in future phylogenomic studies of ants.