| The red harvester ant, Pogonomyrmex barbatus, is widespread throughout deserts and grasslands of southwestern and south-central United States, as well as northern and central Mexico. The application of microsatellite DNA markers to study the genetic structure of a population of P. barbatus colonies near Rodeo, New Mexico, revealed a genetic basis for the queen-worker dimorphism. This genetic system of caste determination is associated with the separation of each species into two distinct genetic lineages. Matings within a lineage give rise to reproductive queens, whereas matings between lineages result in sterile workers, which are necessary to establish a colony. The genetic basis for reproductive caste has implications for the mating system P. barbatus, and imposes constraints on reproductive allocation in P. barbatus colonies. The population of P. barbatus that exhibits an association between genotype and caste has been part of an ongoing behavioral and demographic study for more than two decades. A population genetic analysis of the study population was undertaken to assess how the two lineage system of caste determination affects the mating system and genetic structure of the population. Despite their interdependence, the two genetic lineages found in P. barbatus are highly differentiated at both nuclear and mitochondrial DNA markers. The segregation of the population into two non-recombining lineages affects the evolution of multiple mating by P. barbatus queens, and the estimation of mating frequency by population genetic methods. The genetic composition of P. barbatus colonies, which results from the mating frequency of the colony queen and her pattern of sperm usage, is documented. Finally, while the predominant genetic structure in the population is due to high relatedness within colonies, there is a weak but significant signal of geographic differentiation above the colony level, and a detectable pattern of isolation by distance at the scale of 2 km. |
