Global domination by crazy ants: Phylogenomics reveals biogeographic history and invasive species relationships in the genus Nylanderia (Hymenoptera, Formicidae)

The globally distributed ant genus Nylanderia is among the world's most diverse ant genera, with at least 130 described species and hundreds more undescribed. Fifteen non-native or invasive “crazy ant” species are commonly encountered due to their abundance and widespread distributions. A molecular approach to understanding evolutionary history and revising Nylanderia taxonomy is needed because historical efforts have proven insufficient to define major lineages and determine species boundaries. Nomenclatural problems persist, especially where widespread non-native species are concerned. The disorder and frequent misidentification that has long characterized species-level taxonomy in Nylanderia is a result of the ants' limited morphological variation combined with taxonomists' near-complete dependence on external morphology for species delimitation. To address these problems, we generated the first genus-wide genomic dataset of Nylanderia using ultraconserved elements (UCEs) to resolve phylogeny among hypothesized major lineages, determine the age and biogeographic origin of the genus, and describe global biogeographic patterns. Sampling from seven biogeographic regions revealed an Indomalayan origin of crown Nylanderia and four major biogeographic clades. The Nearctic and Neotropical clades are distantly related, indicating two separate dispersals to the Americas. We also evaluated the integrity of species boundaries in four of the most widespread non-native Nylanderia species by sampling across their ranges and clarified their placement within biogeographic clades. In exhaustively sampling Nylanderia diversity in the West Indies, a “hot spot” for invasive taxa, we found five non-native species among 22 native species; many of these taxa remain morphologically indistinguishable from one another, despite being distantly related.