How Homogenous is a Supercolony? High-Resolution Sequencing Revels Population Genetic Structure in the Introduced Range of Tawny Crazy Ant (Nylanderia fulva (Mayr): Hymenoptera: Formicidae)

Background The tawny crazy ant ( Nylanderia fulva (Mayr)) is native to South America and was first reported in the continental United States (US) in 1938. It was not until the 1990s in Florida and 2000s in Texas that this ant was considered a serious pest in the US. Tawny crazy ant (TCA) is currently considered an invasive pest in six US states. A limited number of low-density molecular markers have previously shown little genetic differentiation among Nylanderia fulva across their geographic distribution in the US. Results Using high-throughput sequencing we obtained high-density molecular markers, a total of 4,557 single nucleotide polymorphisms (SNPs), that provided increased resolution for detecting population genetic differences. There was genetic variation among tawny crazy ants in the US and Argentina. Additionally, there was substructure among some geographic locations in the US (i.e., Texas, Louisiana, Alabama, Mississippi, Georgia, and Florida). Samples from Colombia and Perú were genetically very distant from N. fulva in Argentina and US, and thus they are likely potential cryptic species or belong to another cryptic species complex. Conclusion There is genetic differentiation observed between and within tawny crazy ants in Argentina and the US as well as among tawny crazy ants in the US. Locations associated with port cities in the US are most closely related to ants from Buenos Aires, Argentina. The higher levels of differentiation among other locations and Buenos Aires may be the result of the introduction of an unidentified genotype, admixture, a sample size artifact, or a combination of these factors. Although these tawny crazy ants may act as a supercolony across wide geographic scales, our results support that N. fulva is structured into genetically differentiated populations.