Lack of intraspecific aggression in the ant Tetramorium bicarinatum: a chemical hypothesis.

Tetramorium bicarinatum (Myrmicinae) is an ant species frequently found in tropical and subtropical areas, particularly in Africa, Southeast Asia (Japan), and South America (Brazil). The species is polygynous, reproduces by budding, and has sterile workers. Since the nests are widely distributed in a given area, the problem arises of territorial defense against conspecifics. Because not all ants defend territories, we assessed the defensive behavior of T. bicarinatum workers through intraspecific and interspecific aggressiveness tests. A detailed behavioral study of the interactions between workers from several different colonies of T. bicarinatum (originating from Japan and Brazil) showed that workers do not discriminate against conspecific nonnestmate individuals, but they are highly aggressive towards allospecifics (Myrmica rubra, Myrmicinae). The results suggest that each colony from this ant species possesses a similar colonial odor. Chemical analyses of the cuticular hydrocarbons of these species were made with gas chromatography coupled to mass spectrometry. Results showed that the different colonies of T. bicarinatum possess a common chemical profile mainly composed of straight-chain alkanes and alkenes, while M. rubra possess more methyl-branched alkanes. We suggest that methyl alkane cues play a determining role in colonial recognition and that these results could explain the underlaying basis of the lack of intraspecific aggressiveness in T. bicarinatum.