Lehrstuhl Tierphysiologie, Universität Bayreuth, D-95440 Bayreuth, Germany.
The ability of individuals to discriminate nestmates from alien conspecifics is a pre-requisite for maintaining the integrity of insect colonies. Nestmate recognition is based on colony-specific labels which are supposed to be cuticular hydrocarbons as their compositions are distinguishable between colonies. In some ants there is strong evidence that the hydrocarbon composition (HC) in the postpharyngeal gland (PPG) is largely congruent with that found on the cuticle. In consequence, links between the hydrocarbons of the PPG and cuticular-bound colony-specific recognition cues are hypothesised. In the ant Myrmicaria eumenoides we studied the HC in the PPG and on the cuticle in relation of age and task of ants. The results are: (1) In nursing ants, HCs in the PPG and on the cuticle were congruent. In contrast, in foraging ants, both HCs were modified and compositions in the PPG and on the cuticle differed strongly. Modifications were not due to environmental factors but due to internal factors. (2) Modification of HCs was a continuous process and correlated with the task shift from nursing to foraging. Modification, however, did not correlate with age of ants. (3) When growing older ants could follow two lines: staying in the nest and keeping HCs unchanged or leaving the nest and changing the HCs of PPG and cuticle. Based on our results we conclude that the congruency of hydrocarbons in the PPG and on the cuticle as well as the model of a uniform colony label for each colony - assuming the HCs to be the colony specific labels - are not a general phenomena in ants.