Abstract
The ability of social insects to discriminate nestmates from non-nestmates is mainly achieved through chemical communication. To ultimately understand this recognition and its decision rules, identification of the recognition cues is essential. Although recognition cues are most likely cuticular hydrocarbons, identifying the exact cues for specific species has remained a daunting task, partly due to the sheer number of odor compounds. Perhaps unsurprisingly, one of the few species where the recognition cues have been identified, Formica exsecta, has only around ten major hydrocarbons on its cuticle. In this study we use previous results of this species to search for nestmate recognition cues in two other species of ants, Camponotus aethiops and Monomorium pharaonis. Employing chemical distances and observed aggression between colonies, we first ask which type of data normalization, centroid, and distance calculation is most diagnostic to discriminate between nestmate recognition cues and other compounds. We find that using a “global centroid” instead of a “colony centroid” significantly improves the analysis. One reason may be that this new approach, unlike previous ones, provides a biologically meaningful way to quantify the chemical distances between nestmates, allowing for within-colony variation in recognition cues. Next, we ask which subset of hydrocarbons most likely represents the cues that the ants use for nestmate recognition, which shows less clear results for C. aethiops and M. pharaonis than for F. exsecta, possibly due to less than ideal datasets. Nonetheless, some compound sets performed better than others, showing that this approach can be used to identify candidate compounds to be tested in bio-assays, and eventually crack the sophisticated code that governs nestmate recognition.
Highlights
Kin recognition is a fundamental ability that allows organisms both to avoid inbreeding and to direct cooperative behavior toward related individuals (Hepper, 1991)
THE MOST DIAGNOSTIC COMBINATION OF CALCULATION METHODS In the F. exsecta dataset, the most diagnostic combination is using normalization to percentages, a global centroid and PC1 distance, as this gave the highest ratio between the explained deviance of NMR cues over the explained deviance of task cues (Z-9-alkenes/linear alkanes = 753.08/127.45 = 5.91; see Figure 3)
We look only at the best combination, we find that the explained deviance of the All compound set dropped somewhat, whereas using compound sets NMR cues, High diagnostic power” (DP), Highest 5 DP, or Cluster 1 gave high levels of explained deviance
Summary
Kin recognition is a fundamental ability that allows organisms both to avoid inbreeding and to direct cooperative behavior toward related individuals (Hepper, 1991). Direct evidence for the use of hydrocarbons in nestmate recognition has been obtained in several ant and bee species, by testing the level of aggression toward NMs supplemented with synthetic hydrocarbons (Lahav et al, 1999; Dani et al, 2005; Ozaki et al, 2005; Martin et al, 2008b; Guerrieri et al, 2009), or to inert materials treated with either the hydrocarbon profile of fellow workers or synthetic mixtures of hydrocarbons (Wagner et al, 2000; Akino et al, 2004; Greene and Gordon, 2007; Martin et al, 2008b). Workers whose cuticles were supplemented with a synthetic Z-9-alkene www.frontiersin.org van Zweden et al
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