1Cooperation in ant foundress associations

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The harvester ant Pogonomyrmex californicus has populations that vary in whether queens construct nests alone or form cooperative associations of unrelated queens. These associations last through the lives of the queens and colony. What are the proximate mechanisms and ultimate benefit of cooperative nest founding?

We create laboratory social groups of normally pleometrotic, normally haplometrotic and mixed groups of both types to examine the proximate changes in behavior from solitary to cooperative nest founding, and to assess how individual social phenotype and fitness are affected by the presence of other queens.

2Social regulation of brood production within ant foundress associations

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Our pleometrotic foundress associations become polygynous colonies consisting of multiple queens and their worker offspring.  When these queens lay worker eggs, they contribute to the fitness of the colony, but at metabolic cost to themselves. This sets up the potential for cheating if some queens lay fewer eggs. Do polygynous queens socially regulate egg laying and brood production?

We are assessing maternity of brood and workers in laboratory associations, and conducting field experiments to determine whether queens contribute equitably to producing workers versus their own reproductive offspring.

3Relative success of polygynous versus single-queen colonies at maturity

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Our research suggests that cooperative sociality actually confers fitness benefit to queens during early colony establishment. However, it may conversely generate later reproductive costs at colony maturity. Are queens in polygynous colonies constrained in per capita reproductive output relative to single-queen colonies?

We are addressing this question in a series of field experiments, examining reproductive output and sex skew in our polygynous and single-queen populations. We are additionally addressing the ecological conditions that may influence reproduction, including nutrient availability and colony density.