Recent range expansion of the Argentine ant in Japan
Correspondence: Maki N. Inoue, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.
The Argentine ant, Linepithema humile, has been spreading via human activities from its native range in South America across much of the globe for more than a century. This invasive ant was first detected in Japan in 1993. Its successful world-wide expansion is attributed to a social structure, namely supercoloniality, whereby individuals from separate nests cooperate. Here, we examined the genetic structure of L. humile populations to understand its invasion history.
We analysed mitochondrial DNA of Linepithema humile workers from native and other introduced populations and then integrated previously registered sequences.
Sequencing revealed six haplotypes distributed across its introduced ranges, of which five were present in Japan. The first haplotype was shared by the dominant Japanese, European, North American, Australian and New Zealand supercolonies; the second by the Kobe C supercolony and a Florida population; and the third by the Kobe B and secondary Californian supercolonies and North Carolina colonies. The remaining three haplotypes were each restricted to the Kobe A, Tokyo and Catalonian supercolonies, respectively. Each of the five mutually antagonistic supercolonies was fixed for one of the five haplotypes, and multiple supercolonies were found within a small area.
The large number of haplotypes found in Japan likely reflects the strong propagule pressure of L. humile resulting from the fact that the country is one of the top five importers of trade commodities world-wide. The short invasion history of L. humile in Japan could explain the maintenance of genetic diversity of each independent introduction. In addition, our sampling mostly occurred at major international shipping ports that are likely to be primary sites of introduction. The several recently established L. humile populations within a small area in Japan provide an opportunity to identify the sources of introduction and the local patterns of spread.