Do Defensive Compounds Affect the Success of Invasion of the Argentine Ant?

Abstract

One of the main traits of invasive ants is the formation of supercolonies, large networks of polygynous nests lacking intraspecific competition, which allows them to reach high densities that facilitate their spread. However, different supercolonies exhibit different success in expanding along the world. Here, we explore whether the main chemical defensive compound of the Argentine ant could play a role in the differential invasiveness of supercolonies. We assessed differences in the amount of iridomyrmecin among supercolonies in the native range and in three invasive supercolonies: the Main supercolony (the most extended worldwide), and the Corsican and the Catalonian supercolonies (both with a restricted local distribution in Europe). We found that even if the amount of iridomyrmecin varied greatly between invaded regions in the three supercolonies in Europe and the native supercolonies in South America, the differences did not seem related to the success of invasion. The amount of iridomyrmecin of the Main supercolony was the lowest while the highest corresponded to the Corsican supercolony, with the Catalonian having intermediate values. This suggests that the success of a given invasive supercolony may not be explained by higher quantities of this defensive compound. Alternatively, reducing iridomyrmecin quantities in the invasive range could lead to more investment in other fitness traits that increase the invader's competitive ability. Our results open the way for exploring the contribution of defensive compounds in the competitive ability and spread of this global invader.