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

The ant genus Nylanderia Emery has a cosmopolitan distribution and includes 150 described species and subspecies, with hundreds more estimated to be undescribed. Strong intra- and interspecific morphological variation and few to no diagnostic characters in the worker caste have stalled global taxonomic revision, often necessitating the availability of male specimens for species description and identification. Taxonomy is further complicated because at least 15 Nylanderia species are globetrotters: those which have moved beyond the boundaries of their native range, often through accidental or deliberate transportation by human activity. Nylanderia is one of the most frequently intercepted ant genera at ports of entry worldwide, but identifiers are often unable to provide species-level diagnosis. Seven globetrotting Nylanderia species belong to one of three morphologically difficult species groups: (1) N. bourbonica complex, (2) N. fulva complex, and (3) N. guatemalensis complex. We used target enrichment of ultraconserved elements (UCEs) from 165 specimens collected worldwide representing approximately 98 Nylanderia species to elucidate the phylogenetic position of these three complexes and estimate the number of species and delimit species boundaries within each. For each species complex, allelic phasing was used to separate heterozygous sites in each sample into two haplotypes, effectively doubling sample size and increasing population-level sampling. This phased approach was compared with an unphased approach under the multispecies coalescent. We also extracted the mitochondrial cytochrome C oxidase I (COI) locus from the UCE data to compare our genome-scale results with those using COI barcodes for molecular species delimitation.