RELATEDNESS THRESHOLD FOR THE PRODUCTION OF FEMALE SEXUALS IN COLONIES OF A POLYGYNOUS ANT, MYRMICA-TAHOENSIS, AS REVEALED BY MICROSATELLITE DNA ANALYSIS

The genetic relationships of colony members in the ant Myrmica tahoens is were determined on the basis of highly polymorphic microsatellite D NA loci. These analyses show that colonies fall into one of two classe s. In roughly half of the sampled colonies, workers and female offspri ng appear to be full sisters. The remaining colonies contain offspring produced by two or more queens. Colonies that produce female sexuals are always composed of highly related females, while colonies that pro duce males often show low levels of nestmate relatedness. These result s support theoretical predictions that workers should skew sex allocat ion in response to relatedness asymmetries found within colonies. The existence of a relatedness threshold below which female sexuals are no t produced suggests a possible mechanism for worker perception of rela tedness. Two results indicate that workers use genetic cues, not queen number, in making sex-allocation decisions, (i) The number of queens in a colony was not significantly correlated with either the level of relatedness asymmetry or the sex ratio. (ii) Sex-ratio shifts consiste nt with a genetically based mechanism of relatedness assessment were s een in an experiment involving transfers of larvae among unrelated nes ts. Thus workers appear to make sex-allocation decisions on the basis of larval cues and appear to be able to adjust sex ratios long after e gg laying.