The Antiquity and Evolutionary History of Social Behavior in Bees

A long-standing controversy in bee social evolution concerns whether highly eusocial behavior has evolved once or twice within the corbiculate Apidae. Corbiculate bees include the highly eusocial honey bees and stingless bees, the primitively eusocial bumble bees, and the predominantly solitary or communal orchid bees. Here we use a model-based approach to reconstruct the evolutionary history of eusociality and date the antiquity of eusocial behavior in apid bees, using a recent molecular phylogeny of the Apidae. We conclude that eusociality evolved once in the common ancestor of the corbiculate Apidae, advanced eusociality evolved independently in the honey and stingless bees, and that eusociality was lost in the orchid bees. Fossil-calibrated divergence time estimates reveal that eusociality first evolved at least 87 Mya (78 to 95 Mya) in the corbiculates, much earlier than in other groups of bees with less complex social behavior. These results provide a robust new evolutionary framework for studies of the organization and genetic basis of social behavior in honey bees and their relatives

Casteless sociality in an allodapine bee and evolutionary losses of social hierarchies

Communal behaviour is a form of social behaviour where two or more females nest together and have no reproductive hierarchies. Communal behaviour has often been regarded as an evolutionary ‘stepping stone’ to more complex forms of sociality involving castes, as well as a social form derived from solitary behaviour with no further evolution towards eusociality. However, recent phylogenetic studies on halictine bees suggest that some instances of communal behaviour are derived from eusociality. Here, we describe social nesting in an allodapine bee, Braunsapis puangensis, which has been introduced to Fiji from southern Asia. We show that this bee has a casteless form of sociality similar to communal organization, but which has been derived from an ancestrally hierarchical social system. This is likely due to a combination of small benefits for social nesting that rapidly saturate as colonies become larger, along with low costs for dispersal. We suggest that casteless forms of sociality have frequently evolved from hierarchical societies across many insect groups, but the analyses required for recognizing such societies are often undeveloped and hampers comparative approaches. Transitions from hierarchical to casteless societies challenge the notion that eusociality is an evolutionary ‘end point’ and we argue that eusociality can, in some cases, be regarded as an evolutionary step towards egalitarian societies. We also suggest that evolutionary periods involving reproductive hierarchies could select for traits that allow individuals to better assess their social environment and subsequently enable lower reproductive skew.C. R. B. da Silva, M. I. Stevens, M. P. Schwar