Sociality in the North African small carpenter bee, Ceratina albosticta

Abstract

Small carpenter bees (genus Ceratina) are excellent taxa for studying early stages of social evolution, as they have high within and between species variability in social and parental behavior. Most species of Ceratina studied are facultatively social, with solitary and social nests in sympatry. Here, we examined the nesting and social biology of Ceratina albosticta from populations on the edge of the Sahara Desert in Morocco. Although the majority of nests were solitary, social colonies were relatively common and occurred in 16% of nests. Social nests typically contained two females; however, nests possessing up to four females were also detected. Two-female nests contained four times more offspring on average than solitary nests; therefore, their nest productivity per female was two times higher than in solitary nests. Social nests contained females of similar body size, but the female with larger ovarian development also exhibited greater wing wear. Ovarian dissections and wing wear data suggest that one female performs foraging and reproduction tasks, while the other female serves as a guard. The brood productivity of this facultatively social bee suggests a benefit to social nesting in this species. Moreover, the division of labor observed is recurrent across bee species found in the subfamily Xylocopinae. This is unlike the more traditional queen and worker roles found in the corbiculate and halictid bees, but an interesting and relatively understudied independent origin of eusociality.