Abstract
BackgroundAnts form highly social and cooperative colonies that compete, and often fight, against other such colonies, both intra- and interspecifically. Some invasive ants take sociality to an extreme, forming geographically massive 'supercolonies' across thousands of kilometres. The success of social insects generally, as well as invasive ants in particular, stems from the sophisticated mechanisms used to accurately and precisely distinguish colonymates from non-colonymates. Surprisingly, however, the specific chemicals used for this recognition are virtually undescribed.ResultsHere, we report the discovery, chemical synthesis and behavioural testing of the colonymate recognition cues used by the widespread and invasive Argentine ant (Linepithema humile). By synthesizing pure versions of these chemicals in the laboratory and testing them in behavioural assays, we show that these compounds trigger aggression among normally amicable nestmates, but control hydrocarbons do not. Furthermore, behavioural testing across multiple different supercolonies reveals that the reaction to individual compounds varies from colony to colony -- the expected reaction to true colony recognition labels. Our results also show that both quantitative and qualitative changes to cuticular hydrocarbon profiles can trigger aggression among nestmates. These data point the way for the development of new environmentally-friendly control strategies based on the species-specific manipulation of aggressive behaviour.ConclusionOverall, our findings reveal the identity of specific chemicals used for colonymate recognition by the invasive Argentine ants. Although the particular chemicals used by other ants may differ, the patterns reported here are likely to be true for ants generally. As almost all invasive ants display widespread unicoloniality in their introduced ranges, our findings are particularly relevant for our understanding of the biology of these damaging invaders.
Highlights
Ants form highly social and cooperative colonies that compete, and often fight, against other such colonies, both intra- and interspecifically
We chose five cuticular hydrocarbon (CHC) that differed between colonies for synthesis and behavioural testing and selected two structurally similar CHCs (15-methyl pentatriacontane [15MeC35] and 17-methyl pentatriacontane [17MeC35]) for testing based on ease of synthesis (Figure 1)
To test these chemicals as colonymate recognition cues, we developed procedures to synthesize these CHCs
Summary
Ants form highly social and cooperative colonies that compete, and often fight, against other such colonies, both intra- and interspecifically. Chemical signalling is the most ancient mode of communication and it is still used in some form by all extant organisms [1]. The elaborate social systems of ants, for example, are largely regulated by chemical signals, but very little is known about the chemical labels that define colony membership. Many insects communicate using a class of chemicals known as cuticular hydrocarbons (CHCs). These waxy chemicals probably evolved as barriers to desiccation and microbial infection [3,4], they have since gained functions as cues for various types of recognition and communication (reviewed in [2,5,6]), including courtship [7], speciation [8] and parasitism via aggressive chemical mimicry [9]
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