Colony founding by pleometrosis in the semiclaustral seed-harvester ant Pogonomyrmex californicus (Hymenoptera: Formicidae)

Pleometrosis, or colony founding via multiple queens, occurs in a localized population of the seedharvester ant Pogonomyrmex californicus. In an apparently unusual secondary modification, queens of P. californicus are also obligate foragers; that is, queens must forage to garner the resources necessary to rear their first brood. Laboratory experiments measured the costs and benefits of pleometrosis and queen foraging in P. californicus in terms of queen survival, mass loss by queens and brood production. In all experiments, queen survival was positively associated with number of queens. Queen survival also varied with food level: survival was higher in fed treatments compared with unfed treatments at low queen numbers, whereas survival of unfed queens increased to the level of fed queens at higher queen numbers. Total mass loss of queens varied by food level, but not queen number, with fed queens losing about 50% less mass than unfed queens. Brood production also varied with queen number and food level. Total number of brood was positively associated with number of queens; at each queen number, fed queens produced more brood than unfed queens. The number of brood produced per queen, however, was similar across queen numbers. Fed queens also produced workers that were heavier than those produced by unfed queens, whereas head width of these minims was similar. Longer-term experiments revealed that these queen associations do not undergo queen reduction upon emergence of the first workers, but rather exhibit primary polygyny.