Reproductive potential shapes the expression of nurse-to-forager transition genes in the workers of stingless bees (Meliponini)

Little is known about the molecular mechanisms that underlie the division of labor in stingless bees. We investigated the expression of a set of candidate genes associated with the nurse-to-forager transition in the honey bee in two stingless bee species, Melipona quadrifasciata and Frieseomelitta varia. These species differ with respect to worker reproduction. The workers of M. quadrifasciata lay trophic and reproductive eggs, but those of F. varia are completely sterile. For M. quadrifasciata nurses, we found elevated vitellogenin (Vg) and low juvenile hormone esterase (jhe) transcript levels in the abdomen, in agreement with their reproductive potential. In F. varia, Vg and methyl farnesoate epoxidase (mfe) transcript levels were high in the heads of foragers, indicating an association with foraging behavior. For malvolio (mvl) and foraging (for), both involved with food search behavior, mvl showed persistent low expression in the head, but increasing levels in the abdomen of both species, speaking against a role in behavioral development. The for transcript levels in F. varia were higher in foragers, both in the head and the abdomen, i.e., consistent with foraging. In M. quadrifasciata, however, for expression was higher in the heads of nurse bees, and, thus, is unlikely to play a role in foraging. The results for the two stingless bee species, in comparison with honey bees and bumble bees, indicate that the degree of worker sterility appears to be the primary factor that shapes the expression pattern of key genes in the life history of social bees.