Population genomics of the invasive Argentine ant (Linepithema humile) – adaptive evolution in the introduced supercolonies despite low genetic diversity

The Argentine ant ( Linepithema humile ), native to South America, has spread globally over the past 150 years, forming extremely large supercolonies in its introduced range. Despite the recent demographic history, including founder effects, Argentine ants thrive in the introduced range and displace native ant species. We adopted a comprehensive approach to investigate selection signals across the whole genome of this highly invasive species, with a specific focus on introduced supercolonies. We also investigated genome-wide diversity and divergence patterns and compared the results with earlier microsatellite marker data studies. We used pooled whole-genome sequence data from 100 workers from the species’ native range and each of the three invasive supercolonies – European Main, Catalonia, and Chile. Invasive supercolonies harboured low genetic diversity and were genetically highly differentiated. Despite this, we could detect signs of positive selection in their genomes. Some of the selected genes showed parallel adaptive evolution in invasive supercolonies. Furthermore, there were no signs that a social organisation based on unrelated workers had led to impaired adaptability (genetic meltdown). We conclude that introduced Argentine ant supercolonies evolve adaptively, indicating that founder effects, low genetic diversity and supercolony social organisation do not always hamper species adaptability.