Reduced genetic variation and the success of an invasive species

Despite the severe ecological and economic damage caused by introduced spec ies, factors that allow invaders to become successful often remain elusive. Of invasive taxa, ants are among the most widespread and harmful. Highly i nvasive ants are often unicolonial. forming supercolonies in which workers and queens mix freely among physically separate nests. By reducing costs as sociated with territoriality, unicolonial species can attain high worker de nsities, allowing them to achieve interspecific dominance. Here we examine the behavior and population genetics of the invasive Argentine ant (Linepit hema humile) in its native and introduced ranges, and we provide a mechanis m to explain its success as an invader. Using microsatellite markers, we sh ow that a population bottleneck has reduced the genetic diversity of introd uced populations. This loss is associated with reduced intraspecific aggres sion among spatially separate nests, and leads to the formation of interspe cifically dominant supercolonies. In contrast, native populations are more genetically variable and exhibit pronounced intraspecific aggression. Altho ugh reductions in genetic diversity are generally considered detrimental, t hese findings provide an example of how a genetic bottleneck can lead to wi despread ecological success. In addition, these results provide insights in to the origin and evolution of unicoloniality, which is often considered a challenge to kin selection theory.