The success of alternative reproductive tactics in monogyne populations of the ant Solenopsis invicta: Significance for transitions in social organization

Newly produced queens from monogyne (single-queen) colonies of the ant Solenopsis invicta usually initiate reproduction independently, that is, without worker assistance. However, some recently mated queens attempt to bypass this risky phase of new colony foundation by entering established nests to reproduce, although it is unclear how often these queens are successful in natural populations. We surveyed a mature monogyne population of S. invicta in both 1995 and 1996 for colonies headed by queens incapable of independent colony founding (diploid-male-producing queens) in order to estimate the frequency of colonies that are headed by queens that initiated reproduction within established nests (adopted queens). Using the frequency of diploid-male-producing queens among the recently mated queens in this population, we estimated that the overall rate of queen replacement by adopted queens is about 0.7% per colony per year. Although theory suggests that a change to a novel queen reproductive tactic could be associated with a fundamental change in social organization (queen number), this does not appear to be the case in monogyne S. invicta. However, the evolution of nest-infiltrating reproductive tactics by queens in a monogyne population and the evolution of multiple-queen societies may result from similar ecological pressures facing newly mated queens. We therefore incorporate this strategy into an existing theoretical framework that was developed to explain the evolution of alternative social organizations in ants, providing testable predictions regarding the distribution and frequency of queen adoption in other single-queen ant societies.