Changes in worker polymorphism in Myrmicaria opaciventris Emery (Formicidae, Myrmicinae)

Summary:

The colony ontogeny of Myrmicaria opaciventris was studied by comparing worker number and worker size in foundations with one queen (haplometrosis) or 2 to 6 queens (pleometrosis) and in established colonies. Measurements taken of head width related to scape length showed that the worker caste is weakly polymorphic and exhibits a unimodal size distribution. Classically, the first workers produced in both types of foundations are smaller than those emerging later. Moreover, the worker caste allometry changes with the type of foundation and the age of colony: it varies from a negative allometry for haplometrotic foundations to a stage of isometry in pleometrotic foundations and finally a positive allometry for established colonies. The number of workers produced by the queens is classically larger in pleometrotic than in haplometrotic foundations. However, two uncommon phenomena are described in this species: (1) queen association during colony founding increases their individual fecundity; and (2) the workers produced differ in size and allometry according to the type of foundation.