Regulation of worker reproduction by direct physical contact in the ant Diacamma sp. from Japan

We investigated the function and transmission of signals that regulate worker reproduction in the ponerine ant Diacamma sp. from Japan, in which the morphological queen caste is absent and a mated worker (gamergate) reproduces as a functional queen in each colony instead. An inhibitory effect of a gamergate pheromone has been inferred in this species, because virgin workers frequently lay eggs in colonies without a gamergate, but rarely do so in the presence of one. We restricted the movements of gamergates and workers in experimental nests: one group of workers-always had a gamergate present; another group had no gamergate; and a third group could choose between having contact with a gamergate and avoiding contact. Only workers that had no contact with a gamergate were aggressive and developed ovaries with fully mature oocytes. The gamergate signal was thus nonvolatile and passed on only by direct physical contact with workers. Theoretically, there should be a gamergate-worker conflict over male production; however, workers apparently responded to the gamergate's presence by refraining from egg laying. The gamergate signal may inform workers of the presence of a gamergate who can police their reproduction. Even when given the opportunity to avoid direct contact with the gamergate and thereby escape its policing, the workers did not do so and never oviposited. This behaviour-may be a kin-selected trait, which mediates workers' sterility and in turn enhances colony efficiency.