Sex allocation in a facultatively polygynous ant: between-population and between-colony variation

We investigated sex allocation in three U.K. populations ofthefacultatively polygynous ant Leptothorax acervorum over1-3 years.The first main finding was that, across sites, thepopulation sex-investmentratio changed from significantly femalebiased to significantly male biasedwith increasing polygyny.This was consistent with workers controlling sexallocationand reacting to changes in their population-level relatednessasymmetry.It was also consistent with local resource competition due toreproductionby colony budding under polygyny. Worker control was supportedbythe finding that queen number had no effect on sex allocationamong polygynouscolonies. The second main result was that monogynouscolonies consistentlyproduced more female-biased sex-investmentratios than polygynous colonies inone site only (Santon). Theresults from Santon supported both the relativerelatednessasymmetry hypothesis and the idea of sex ratio compensationdue tocolony budding. The workers' response to their population-levelrelatednessasymmetry reinforced the case for relatedness asymmetrybeing influential atthe colony level. The other populationscould have lacked split sex ratiosbecause polygynous colonieswere either comparatively rare or common, makingthem behaveas almost entirely monogynous (Aberfoyle) or polygynous (Roydon)populations.In Roydon, this was consistent with the inference from allozymedatathat monogynous and polygynous colonies did not differ in theirworkerrelatedness asymmetries. The final principal findingwas that, of hypotheseslinking the colony sex-investment ratiowith sexual productivity, there wassupport for the constantfemale hypothesis but not for the constant male, costvariation,or multifaceted parental investment hypotheses.