NESTMATE RECOGNITION IN THE ANT CATAGLYPHIS NIGER - DO QUEENS MATTER

This study compares two basic models for the origin and maintenance of colony gestalt odor in the polygynous ant species Cataglyphis niger. In the first model, queens are centers of de novo biosynthesis and dis tribution of recognition odors (''queen-centered'' model); in the seco nd, colony odors are primarily synthesized and distributed by workers (''worker-centered'' model). We tested the behavioral patterns that ar e predicted from each model, and verified by biochemical means the dis tributional directionality of these signals. Encounters between nestma tes originating from split colonies were as amicable as between nestma tes from non-split colonies; queenless ants were as aggressive as thei r queenright nestmates, and both were equally aggressed by alien ants. These results indicate that queens have little impact on the recognit ion system of this species, and lend credence to the worker-centered m odel. The queen-centered model predicts that unique queen substances s hould be produced in appreciable quantities and that, in this respect, queens should be more metabolically active than workers. Analysis of the chemical composition of postpharyngeal glands (PPGs) or cuticular extracts of queens and workers revealed high similarity. Quantitativel y, queens possessed significantly greater amounts of hydrocarbons in t he PPG than workers, but the amount on the thoracic epicuticle was the same. Queens, however, possess a lower hydrocarbon biosynthesis capab ility than workers. The biochemical evidence thus refutes the queen-ce ntered model and supports a worker-centered model. To elucidate the di rectionality of cue distribution, we investigated exchange of hydrocar bons between the castes in dyadic or group encounters in which selecti ve participants were prelabeled. Queens tended to receive more and giv e less PPG content, whereas transfer to the epicuticle was low and sim ilar in all encounters, as predicted from the worker-centered hypothes is. In the group encounters, workers transferred, in most cases, more hydrocarbons to the queen than to a worker. This slight preference for the queen is presumably amplified in a whole colony and can explain t heir copious PPG content. We hypothesize that preferential transfer to the queen may reflect selection to maintain her individual odor as cl ose to the average colony odor as possible.