Acomprehensive study on invasive aliea species and supercolonies of ants

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In this research on Formica yessensis which exhibits a supercolony on the coast of Ishikari, Hokkaido, We confirmed the presence of a chemosensory sensillum which was previously discovered in workers of a phylogenetically close ant Camponotus japonica. Whereas the sensillum responded even to hydrocarbons of nestmates, the response was less intense than that to hydrocarbons of workers from other colonies, indicating that this organ of F. yessensis retains the function of nestmate recognition. Within the supercolony, the response of the sensillum was significantly correlated with the geographic distance of the analyzed nests, suggesting that there is a little antagonistic relationship even between the nests which do not show any aggressive behaviors. The presence of the antagonistic relationship between the supercolonial nests was also suggested by a mathematical analysis of the behavioral data which was obtained in the outdoor observation of F. yessensis workers. Moreover, the analysis of microsatellite DNA demonstrated that the kin relatedness within the supercolony was as low as that between different colonies. Although the intranidal kin relatedness was a little higher, the standard deviation was high, indicating that the nestmates were composed not only of kins but also of non-related workers and queens. These results suggest that the kin selection is not an important factor to maintain the supercolony. Probably, one of more important factors is the strong wind which often blows flying alates to the sea and accordingly offers advantages to the post-mating queens which abandon the flight and enter the natal or neighboring nests. The relatively homogeneous habitat on seaside dune may be another key factor which facilitated the development of polygyny and the reduction of internidal antagonism on the Ishikari Coast.