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Rhytidoponera sp. 12 A.N.I.C. is a queenless Australian arid zone ant with multiple mated workers (= gamergates) breeding in the colonies. Rhytidoponera sp. 12 colonies are classified as Type 1 with full sisters, or Type 2 with related females from overlapping generations as co-existing gamergates. While Type 2 colonies can arise from workers accepting mated nestmates into the natal colony, the origin of Type 1 colonies is more difficult to explain, as no monogynous colony founding stage is known in this species. We applied microsatellites to study colony kin structure and its temporal variation over three sampling years, and used the data to infer colony-founding strategies and reproductive dominance. The average worker relatedness was always significantly higher than zero, but it differed greatly between colonies within each sampling occasion, ranging from approximately zero to 0.34. Furthermore, worker relatedness fluctuated in individual colonies over the sampling period, probably reflecting different stages of colony life cycles. Although gamergates lack dominance behaviour, assumption of some degree of reproductive skew must be invoked to explain the discrepancy between worker nestmate relatedness and the theoretical expectation based on the observed number of gamergates and relatedness among them. The effective (genetic) turnover rate of gamergates was 17% per year. This estimate results probably not only from actual changes in the gamergate pools, but also from changes in the reproductive skew between the gamergates. Incorporating gamergate relatedness estimates with worker nestmate relatedness estimates over multiple years suggested that one alternative for the origin of Type 1 colonies could be colony fission that involves kin-association between gamergates along mainlines.