Reproductive conflict among ant workers inDiacamma sp. from Japan: dominance and oviposition in the absence of the gamergate

Summary Queens do not exist inDiacamma sp. from Japan, and a single worker (gamergate) mates and monopolizes reproduction in each colony. We isolated small groups of workers without the gamergate, and confirmed that after 7–15 days many workers were able to oviposit (Tab. 1). These egg-laying individuals engage in stereotyped attacks towards each other. In six groups of individually marked workers (Tabs. 3 to 7), the pattern of aggressive interactions always indicated that one worker was dominant. She usually initiated a large number of attacks, but was herself never attacked. This dominant worker (alpha) also ate the eggs just laid by others. There was no linear dominance hierarchy, although a second highest-ranking worker could be recognized (she was only attacked by alpha). When these workers were dissected 4–6 weeks after being orphaned, only the alpha worker had active ovaries; other individuals that had been observed to oviposit earlier exhibited resorbed ovaries. Dissection of another 12 orphaned groups, kept together for different periods of time (Tab. 2), confirmed that one dominant worker is able to suppress the ovarian activity of all others in her group. We discuss how these aggressive interactions also function to regulate the production of males in other contexts, even when the gamergate is present. This aggression is separate, however, from another competitive interaction, mutilation of the gemmae, that functions as a control of mating activity in this species.