Sex Allocation and Colony Maintenance in Monogyne and Polygyne Colonies of Formica truncorum (Hymenoptera: Formicidae): The Impact of Kinship and Mating Structure

Abstract

The aim of this article is to discriminate between genetic (worker-queen conflict) and ecological (mating structure, colony productivity) determinants of resource allocation in ants. Both the allocation to growth versus reproduction (reproductive allocation) and the allocation to males versus females (sex allocation) were analyzed as a function of colony kin structure, colony productivity, and mating structure in monogyne and polygyne populations of the ant species Formica truncorum. Colonies headed by single queens (monogyne colonies) were smaller and produced more sexuals per adult worker than those with multiple queens (polygyne colonies). Monogyne colonies with a high total production relative to colony size invested excess resources in reproduction, whereas the reproductive allocation did not change with increased productivity in polygyne colonies. The results suggest that workers control reproductive allocation. The population-level sex ratio was female biased in the monogyne population and male biased in the polygyne population. The colony-level variation in sex allocation in the monogyne colonies was best explained by variation in relatedness asymmetry (the relative relatedness of workers to males vs. females) among colonies, together with colony size and the percentage of sexuals in the brood (r2 = 0.77). In polygyne colonies male bias increased with increasing production of sexuals, which suggests that local resource competition was the main determinant of colony-level sex-allocation variation in these colonies.