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. For example, the European Main supercolony spans over 6,000 km along the Mediterranean coastline. Despite the recent demographic history, including founder effects, Argentine ants thrive in the introduced range and displace native ant species. We took a comprehensive approach to investigate this highly invasive species’ recent demographic history and genome evolution, primarily focusing on introduced supercolonies. We used pooled whole genome sequence data of 100 workers from the species native range and each of the three invasive supercolonies – European Main, Catalonia, and Chile. Invasive supercolonies were highly differentiated from each other and harboured low genetic diversity. Despite this, we could detect signs of positive selection in their genomes – both supercolony-specific and shared patterns. Positively selected genes overlapped the most across invasive supercolonies, indicating altered and shared selective pressure in new habitats. These included, e.g., genes implicated in neurobiological functions. Moreover, we found balancing selection, both supercolony-specific and shared patterns, including many chemical signalling genes. We conclude that introduced Argentine ant supercolonies evolve adaptively, indicating that founder effects and low genetic diversity do not always hamper adaptability.