Longitudinal sampling reveals a dynamic behavioral and genetic landscape in the Argentine ant large supercolony

The supercolonies of invasive ants are largest societies on Earth. Although this colony structure is rare in ants generally, invasive ants often transition from smaller ancestral colony structures in their native ranges to enormous, geographically widespread supercolonies in their introduced ranges, thus gaining ecological advantages through reduced intraspecific competition and increased population sizes. Historically, a single large supercolony (“LSC”) of the Argentine ant (Linepithema humile) has dominated nearly all of the introduced range in California. In this study, we assessed the long-term behavioral, genetic, and cuticular hydrocarbon (CHC) profile stability of LSC in California. We resurveyed 21 sites where L. humile colony identity was characterized between 1997-2007, 17 of which belonged to the LSC. In our 2022-2024 resurvey, we found that six of the 17 LSC sites are now occupied by different supercolonies, the majority belonging to the Lake Hodges population, which was present at only two sites in the initial survey. Using genomic data from ants collected at both timepoints, we found that genetic clusters are consistent with colony assignments made based on behavioral and CHC analysis. While we observed small changes in genetic diversity between the first and second survey periods, more variation was found between supercolonies rather than between sites or timepoints. Our results demonstrate that individual supercolonies can persist over multi-decadal time periods but, at the same time, over 1/3 of sites that initially belonged to LSC have been replaced by conspecific competitors.