Body size, demography and foraging in a socially plastic sweat bee: a common garden experiment

摘要

Phenotypic plasticity may evolve when conditions vary temporally or spatially on a small enough scale. Plasticity is thought to play a central role in the early stages of evolutionary transitions, including major transitions such as those between non-sociality and sociality. The sweat bee Halictus rubicundus is of special interest in this respect, because it is socially plastic in the British Isles: Nests are social or non-social depending on the environment. However, sociality comprises a complex suite of inter-related traits. To further investigate social plasticity in H. rubicundus, we measured traits that are potentially integral to social phenotype at a northern site, where nests are non-social, and a southern site where nests can be social. We found that foundresses at non-social sites were smaller, produced offspring of a size more similar to themselves, initiated nesting later, and took longer to produce their first female offspring. They began provisioning earlier in the day, finished earlier, and collected more pollen loads. Common garden experiments suggested that these differences represent mainly plasticity, as expected for traits involved in the overall plastic social phenotype, with only limited evidence for fixed genetic differences in foraging. Conditions during overwintering did not have major effects on a foundress' subsequent behaviour.