Two widely separated populations (central Arizona and southern California) of the seed-harvester ant Pogonomyrmex californicus vary in colony founding behavior and queen morphology/physiology. In central Arizona, single queens found colonies, whereas multiple, apparently unrelated queens found colonies in southern California. In both populations queens display the primitive behavior of foraging.
Patterns of queen survival and worker production vary between populations. Foraging is obligatory in the Arizona population of P. californicus as single queens can survive and eclose workers only when provided food. In the California population, single unfed queens also have low success at eclosing workers, but multiple unfed queens commonly eclose workers. Pleometrosis also enhanced queen survival, which progressively increased from one to five queens. These data support the hypothesis that joining groups is advantageous when haplometrotic colony founding is risky. The pleometrotic population also exhibits primary polygyny rather than the more typical pattern in which colonies reduce to monogyny after workers eclose.
Physiological traits also differed between the two populations. In central Arizona, queens exhibited a low fat content, lack of storage proteins, and a low queen-worker size dimorphism relative to that of fully claustral congeners. Alternatively, queens from southern California had a fat content similar to that of claustral congeners, and a queen-worker dimorphism intermediate to the Arizona population and fully claustral congeners. Colony growth rate also appears to be faster for single queens from Arizona relative to those from California. Moreover, behavioral and physiological differences indicate the possibility of incipient speciation. This conclusion is supported by seasonal differences in mating flights (late May-early June in Arizona, late June-early July in California), which effect reproductive isolation of the two populations.
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA