The breeding system of the fire ant Solenopsis invicta: effects on colony genetic structure.

Genetic and observational data are combined to describe the breeding system in a polygyne population of Solenopsis invicta using a formal theoretical framework that links properties of the breeding system with colony genetic structure. Queens of S. invicta mate only once, and the study population is outbred. The number of mated queens per nest is variable but generally low, with the average relatedness of nest-mate queens indistinguishable from zero. The genetic data are sufficiently complete that worker relatedness in individual nests can be estimated accurately, and the values obtained are shown to be well accounted for by the number of queens present in each nest. Thus, variance in maternity apportionment among nest-mate queens or internest movement of ants need not be invoked as determinants of colony genetic structure. Average worker nest-mate relatedness results from the opposing effects of two groups of factors: single mating by queens and the apparent closed nature of the societies elevate relatedness, while the presence of multiple queens and their low relatedness to one another depress it. This study also reveals consistent differences within nests in the matrilineal composition of worker and queen brood. This constitutes further evidence for inequities among nest-mate queens in the allocation of their progeny to the two castes at a single point in time.