Reproductive Investment and Allocation Ratios for the Ant Leptothorax longispinosus: Sorting Out the Variation

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Abstract
Sex-ratio theory as applied to social Hymenoptera has implicated a large number of factors than can affect predictions about sexual allocation. I examine these factors for the tiny forest ant Leptothorax longispinosus by applying Sewall Wright''s path analysis to 10 yr of data from two geographical locations. Populations in Vermont and New York were similar with respect to nest sizes and the patterns of queen number but differed strongly in reproduction parameters. Nests in Vermont reared smaller sexuals and produced broods that were more male-biased than their counterparts in New York. Path analysis allowed the exclusion of differential rearing costs, local resource competition, and local mate competition: furthermore, it implicated conflict between queens and workers over alate masses, total investment in sexuals, and allocation to females. Despite considerable explanatory power, variation residual after path analysis showed that unmeasured parameters were important for reproduction patterns in this species. The most likely unmeasured determinants were resource-acquisition ability, not adequately estimated by worker number, and investment in colony growth. Given the immense variability in allocation ratios typically observed for social insects, conclusions concerning patterns of reproduction must be predicated on large data sets collected over several seasons and at different sites.