EXPERIMENTAL INVESTIGATION OF THE MECHANISM OF REPRODUCTIVE DIFFERENTIATION IN THE QUEENLESS ANT, DIACAMMA SP., FROM JAPAN

We test two hypotheses about regulation of the reproductive division o f labour in the permanently queenless ponerine ant, Diacamma sp., from Japan. All workers emerge with gemmae (:tiny innervated thoracic appe ndages), but only one individual keeps them in each colony, and she is the only mated reproductive worker (gamergate). The gemmae of all oth er workers; are mutilated by the gamergate soon after their emergence, and they can never mate. In the presence of gamergate, mutilated work ers have inactive ovaries and do not behave aggressively. Two possible consequences of mutilation are: 1. olfactory signal-a pheromone inhib iting the oogenesis of mutilated workers is no longer released by the gemmae; and 2. endocrine degeneration of its afferent neuronal connect ions interferes reproductive physiology of a gamergate. Gemmae of game rgates were coated with shellac (to prevent pheromone emission) or rem oved, and over three weeks we studied any changes in ovarian activity of the gamergates as well as nestmate workers. Coating of gemmae did n ot elicit worker oviposition,suggesting that gemmae pheromones do not have a regulatory function. Experimental mutilation of gamergates resu lted in a slight increase in both the frequency of dominance interacti ons and the ovarian activity of mutilated workers, but this effect was much lower than in colonies where the gamergate was removed. This con trasts with the immediate change in the behaviour (aggressive to timid ) of newly emerged workers following mutilation.