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In this dissertation, I evaluate the ecological drivers and fitness consequences of non-kin queen cooperation, by comparing the reproduction of mature single-queen versus polygynous harvester ant (Pogonomyrmex californicus) colonies in the field. I captured and quantified the total number and biomass of reproductives across multiple mating seasons, comparing between populations that vary in the proportion of single queen versus polygynous colonies, to assess the fitness outcomes of queen cooperation. Colonies in a mainly polygynous site had lower reproductive investment than those in sites with predominantly single-queen colonies. The site dominated by polygyny had higher colony density and displayed evidence of resource limitation, pressures that may drive the evolution of queen cooperation.
I also used microsatellite markers to examine how polygynous queens share worker and reproductive production with nest-mate queens. The majority of queens fairly contribute to worker production and equally share reproductive output. However, there is a low frequency of queens that under-produce workers and over-produce reproductive offspring. This suggests that cheating by reproducing queens is possible, but uncommon. Competitive pressure from neighboring colonies could reduce the success of colonies that contain cheaters and maintain a low frequency of this phenotype in the population.
Much is still unknown about dominance hierarchies. Many different species form dominance hierarchies and each species have very different ways of forming these hierarchies. Some engage in various different dominance interactions to establish a dominant position. This experiment aims to use the ant species, Harpegnathos saltator, as a model to explore what sets dominant individuals, or gamergates in this case, apart from non-dominant individuals, or non-gamergates. H. saltator ants perform various different behaviors such as dueling, which is a mutually beneficial behavior, dominance biting, which is an aggressive behavior, and policing which is used to bring down those who are dominant. These behaviors can be used to study the importance of initiation and aggression in hierarchy formation. This experiment will explore how aggression through dominance biting, duel initiation, group size, and time period affect the formation of gamergates. To do so, socially unstable colonies of 15, 30, and 60 ants were video recorded for days until gamergates were established. Then, from the recordings, a period of high activity was selected and observed for dueling, duel initiation, dominance biting, dominance bite downs, and policing. The results showed that gamergates tended to perform dominance biting and dominance bite downs far more than non-gamergates during the period of high activity, but not as clearly with duelling and duel initiations. It was inconclusive whether or not the combination of both dueling and dominance biting was what set gamergates apart from non gamergates as different groups showed different results. Gamergates performed visibly more dominance bite downs than non-gamergates, so aggression may be important in setting gamergates apart from non-gamergates. In terms of group size, the smallest group had the least number of gamergates and the least activity, and the medium and large group had a similar number of gamergates and activity.