Phylogenomic Delimitation of Morphologically Cryptic Species in Globetrotting Nylanderia (Hymenoptera: Formicidae) Species Complexes

Abstract The ant genus Nylanderia Emery has a cosmopolitan distribution and includes 150 extant described species and subspecies, with potentially hundreds more undescribed. Global taxonomic revision has long been stalled by strong intra- and interspecific morphological variation, limited numbers of diagnostic characters, and dependence on infrequently collected male specimens for species description and identification. Taxonomy is further complicated by Nylanderia being one of the most frequently intercepted ant genera at ports of entry worldwide, and at least 15 globetrotting species have widespread and expanding ranges, making species-level diagnoses difficult.Three species complexes (‘bourbonica complex’, ‘fulva complex’, and ‘guatemalensis complex’) include globetrotting species. To elucidate the phylogenetic positions of these three complexes and delimit species boundaries within each, we used target enrichment of ultraconserved elements (UCEs) from 165 specimens representing 98 Nylanderia morphospecies worldwide. We also phased the UCEs, effectively doubling sample size and increasing population-level sampling. After recovering strong support for the monophyly of each complex, we extracted COI barcodes and SNPs from the UCE data and tested within-complex morphospecies hypotheses using three molecular delimitation methods (SODA, bPTP, and STACEY). This comparison revealed that most methods tended to over-split taxa, but results from STACEY were most consistent with our morphospecies hypotheses. Using these results, we recommend species boundaries that are conservative and most congruent across all methods.This work emphasizes the importance of integrative taxonomy for invasive species management, as globetrotting occurs independently across at least nine different lineages across Nylanderia.