SEROTONIN CONVERTS MATING HISTORY INTO BEHAVIOURAL STRATEGY

Across an animal’s life, the same sensory world can demand very different strategies: sometimes it pays to keep sampling and pursuing opportunity, other times to let experience constrain future action. We use male Drosophila to ask how the mating state enforces such a strategy shift across behaviours. Here, we show that a single mating coordinately promotes aversive long-term memory (LTM), suppresses exploration, and reduces risk-taking under motivational conflict through a pair of serotonergic neurons (SPNs). Virgins form short-term aversive memory yet fail to consolidate aversive LTM, and they show heightened novelty seeking in a Y-maze and sustained exploration in an open field; mating reverses these profiles. SPN-specific knockdown of the cAMP phosphodiesterase dunce (dnc) in virgins is sufficient to phenocopy the mated state, reducing exploration while enhancing aversive LTM. In an assay requiring males to cross an electric shock barrier to access a mating partner, virgins show higher approach than mated males, and disrupting mating-state signalling to SPNs restores high approach in mated males. Mechanistically, in vivo imaging reveals that inhibiting dnc boosts serotonin release from SPNs, identifying a molecular lever that can tune this state-dependent switch. Together, these findings identify SPNs as a state-sensitive hub that converts mating history into a unified ethological strategy, aligning aversive LTM consolidation, exploration, and risk taking with reproductive state.