Juvenile hormone in a facultatively-social bee is associated with development and reproduction, but not sociality

Eusocial Hymenoptera are characterized by specialization of foraging and reproductive phenotypes that are absent in their solitary ancestors. Hymenopteran species that are facultatively-social, where some populations show solitary living and social ones show a clear distinction between reproductive and non-reproductive individuals, can hint at the physiological shifts associated with the evolution of eusociality. In addition to its role as a regulator of development and reproduction in insects, Juvenile Hormone (JH) pathways are thought to be central to the evolution of insect eusociality. While there is some consistency in the way that JH signaling has been used in caste differentiation and reproduction across diverse bee lineages, the specific effects of JH can differ by taxon and social context. Elucidating the function(s) of JH signaling within a facultatively-social species can therefore enhance our understanding of its role in the evolution of eusociality in bees. Here, we examined JH titers in the small carpenter bee (Ceratina calcarata) in relation to its developmental stage, sex, body size, age and social organization. We found that JH titer increases after adult eclosion and is linked to a mother’s fecundity independent of her age and body size. The JH levels of social daughters and mothers did not differ from solitary ones, however. In concert with recent findings of a gonadotropic role of JH in Xylocopa, JH likely regulates development and fecundity across carpenter bees (Xylocopinae). But in contrast to other insect lineages, JH signaling in carpenter bees may not be very sensitive to social context.