Task allocation and reproductive skew in social mass provisioning carpenter bees in relation to age and size

The mass provisioning carpenter bees comprise two tribes, the Xylocopini an d the Ceratinini. Although social nesting occurs in both tribes, no morphol ogical castes have evolved and females are totipotent, which makes the trib e as a whole highly suitable to test predictions of reproductive skew model s. We review current information for the two tribes with respect to reprodu ctive competition and reproductive skew and then investigate whether the ob served skew fits with predictions from optimal skew theory. Social nests of Xylocopa species include a non-foraging guard and a foraging egg layer who completely dominates reproduction. Reproductive dominance is settled by ag gression, and the probability of winning this fight is influenced by both a ge and size. In Ceratina species, task allocation is also very clear: one f emale guards the nest, while the other female(s) forage(s). Although the gu ard is usually the first to produce an egg, her eggs are frequently replace d by those of the forager, and skew is incomplete. Using comparisons between species and genera the impact of ecological const raints on solitary nesting, relative group productivity and relatedness on reproductive partitioning between dominants and subordinates are investigat ed in a qualitative way. In support of the optimal skew model, strong const raints on solitary nesting coincided with strong skew However, the predicte d effects of relatedness and group productivity on skew were not found. Fur thermore, no support was found for the predictions of the optimal skew mode l that high skew coincides with frequent aggressive testing and risky task performance by subordinates.