Reversible plasticity in brain size, behavior, and physiology characterizes caste 2 transitions in a socially flexible ant (Harpegnathos saltator)

Phenotypic plasticity allows organisms to respond to changing environments throughout their lifetime, but these changes are rarely reversible. Exceptions occur in relatively long-lived vertebrate species that exhibit seasonal plasticity in brain size, although similar changes have not been identified in short-lived species, such insects. Here we investigate brain plasticity in reproductive workers of the ant Harpegnathos saltator. Unlike most ant species, workers of H. saltator are capable of sexual reproduction, and they compete in a dominance tournament to establish a group of reproductive workers, termed “gamergates.” We demonstrated that, compared to foragers, gamergates exhibited a 19% reduction in brain volume in addition to significant differences in behavior, ovarian status, venom production, cuticular hydrocarbon profile, and expression profiles of related genes. In experimentally manipulated gamergates, 6-8 weeks after being reverted back to non- reproductive status their phen...