1Theodor-Boveri-Institut, LS Verhaltensphysiologie und Soziobiologie, 97074 Würzburg, Germany. 2Laboratoire d'Ecologie, CNRS UMR 7625, Université Pierre et Marie Curie, Paris, France.
Ant queens generally monopolize reproduction, and this is associated with the emission of pheromones which are hypothesized to either directly inhibit the ovaries of workers, or provide honest information on the basis of which workers optimize their inclusive fitness (e.g. Ratnieks, 1988, Am. Nat. 132:217, Keller & Nonacs 1993, Anim Behav.45: 787). We attempted to identify the source and chemical nature of this "queen signal" in Harpegnathos saltator, a species in which founding queens and mated egg-laying workers (gamergates) alternate (Peeters C & Hölldobler, 1995 PNAS 92:10977). We expected this signal to be present on the cuticle, as was shown in another queenless ant (Monnin et al 1998, J Chem Ecol 24:473). GC/MS-analysis of cuticular washes identified hydrocarbons with chain lengths ranging from 23 to 39. Cuticular hydrocarbons on the gaster were extracted by solid-phase microextraction, and GC analysis revealed that the profile of gamergates, egg-laying queens and non-reproductive individuals show qualitative differences in nine compounds. The rest of the compounds (N=14) differ qualitatively between infertile and reproductive individuals as was revealed by discriminant analysis. When previously infertile workers become reproductive they develop the characteristic gamergate profile within less than 76 days. The differences in the hydrocarbon-profiles between reproductives and non-reproductive individuals is not caused by a single compound but involve a complete shift in chain length of all compounds. In this ant species the cuticular hydrocarbons reflect physiological status associated with ovarian activity rather than being a consequence of pre-imaginal differentiation.