Genome-wide SNPs reveal the social structure and invasion pathways of the invasive tropical fire ant (Solenopsis geminata)

Elucidating invasion pathways of invasive species is often challenging because invasive populations frequently have low genetic diversity caused by genetic bottlenecks during introduction events. Genome-wide sequencing such as Restriction Site-Associated DNA Sequencing (RADseq) can overcome these challenges by generating thousands of genome-wide single nucleotide polymorphic (SNP) markers. The tropical fire ant, Solenopsis geminata, is a global invader with low genetic diversity in its introduced range, making RADseq one of the best available methods to investigate its population genetics. We used double digest RADseq to generate 3,834 SNPs to compare the genetic diversity of S. geminata in its introduced range to its most likely source of introduction, determined the invasion pathways among populations at an unprecedented level of detail for this species, and determined the social structure of S. geminata workers collected in 13 locations worldwide. We found that introduced S. geminata went through a strong genetic bottleneck. We also identified multiple secondary introduction events among S. geminata populations, indicating that the bridgehead effect is an important driver in the global spread of this species. We found that all colonies in the introduced range were polygyne (i.e., with more than one queen) which may increase their invasion success and potential to cause adverse effects.