Task partitioned nectar transfer in stingless bees (Meliponini): work organisation in a phylogenetic context.

1. The eusocial corbiculate bee tribes comprise the Apini (honey bees), Bombini (bumble bees), and Meliponini (stingless bees). Honey bee foragers (Apis) transfer nectar to receiver bees within the nest. This is an example of task partitioning, in which a task is split into sub-tasks connected by material transfer. Nectar transfer does not occur in Bombini. Although it is reported in some species of Meliponini, it has not been subject to detailed study. 2. Nectar transfer was investigated in five genera of Meliponini from Yucatan, Mexico (Melipona, Trigona, Scaptotrigona, Nannotrigona, and Plebeia). Nectar transfer occurred in all species and for > 99% of foragers. Multiple transfer, in which a forager unloads nectar to more than one receiver, occurred but at a lower level than in Apis. In M. beecheii, multiple transfer was associated strongly with putative recruitment dances. 3. The data provide some support for the hypothesis that task partitioning is favoured by large colony size, in that the Meliponini never have small colonies because colonies are swarm founded. This ensures that colonies are always large enough to prevent delays in finding a transfer partner imposing high costs. Further tests of this hypothesis are suggested. 4. Viewed in a phylogenetic context, the most parsimonious interpretation is that nectar transfer evolved once in the clade (Apini + Meliponini).