Carolina Rezaval

To survive, animals must balance opportunity and risk, yet how internal motivational state biases this trade-off remains poorly understood. Here we show that hunger gates nociceptive avoidance in Drosophila to enable food approach under conflict. Using a behavioural assay in which flies must cross an electric shock barrier to reach food, we find that starvation promotes shock tolerance only when food-related olfactory cues are present. This state- and context-dependent behavioural shift is mediated by a defined neuromodulatory circuit. Leucokinin neurons encode hunger and convey this information to PV5K1 lateral horn output neurons, which integrate internal state signals with food odour cues and suppress shock-responsive FB2B neurons in the ventral fan-shaped body. Accordingly, electric shock–evoked activity in FB2B neurons is suppressed in starved flies exposed to food cues. These findings identify a circuit mechanism by which motivational state gates aversive processing to bias action selection towards goal-directed behaviour. Teaser: Hunger enables flies to suppress nociceptive avoidance when food cues signal reward availability via a defined neuromodulatory circuit.

Romantic engagement can bias sensory perception. This ‘love blindness’ reflects a common behavioural principle across organisms: favouring pursuit of a coveted reward over potential risks¹. In the case of animal courtship, such sensory biases may support reproductive success but can also expose individuals to danger, such as predation^2,3. However, how neural networks balance the trade-off between risk and reward is unknown. Here we discover a dopamine-governed filter mechanism in male Drosophila that reduces threat perception as courtship progresses. We show that during early courtship stages, threat-activated visual neurons inhibit central courtship nodes via specific serotonergic neurons. This serotonergic inhibition prompts flies to abort courtship when they see imminent danger. However, as flies advance in the courtship process, the dopaminergic filter system reduces visual threat responses, shifting the balance from survival to mating. By recording neural activity from males as they approach mating, we demonstrate that progress in courtship is registered as dopaminergic activity levels ramping up. This dopamine signalling inhibits the visual threat detection pathway via Dop2R receptors, allowing male flies to focus on courtship when they are close to copulation. Thus, dopamine signalling biases sensory perception based on perceived goal proximity, to prioritize between competing behaviours.

Romantic engagement can bias sensory perception. This ’love blindness’ reflects a common behavioral principle across organisms: favoring pursuit of a coveted reward over potential risks. In the case of animal courtship, such sensory biases may support reproductive success but can also expose individuals to danger, such as predation. How do neural networks balance the trade-off between risk and reward? Here, we discover a dopamine-governed filter mechanism in male Drosophila that reduces threat perception as courtship progresses. We show that during early courtship stages, threat-activated visual neurons inhibit central courtship nodes via specific serotonergic neurons. This serotonergic inhibition prompts flies to abort courtship when they see imminent danger. However, as flies advance in the courtship process, the dopaminergic filter system reduces visual threat responses, shifting the balance from survival to mating. By recording neural activity from males as they approach mating, we demonstrate that progress in courtship is registered as dopaminergic activity levels ramping up. This dopamine signaling inhibits the visual threat detection pathway via Dop2R receptors, allowing male flies to focus on courtship when they are close to copulation. Thus, dopamine signaling biases sensory perception based on perceived goal proximity, in order to prioritize between competing behaviors.

Naive males court both virgin and mated females but learn through experience to discriminate between them, thus minimizing futile investments in nonreceptive female flies. In the laboratory, we can exploit the innate courtship enthusiasm of males and manipulate their behavior by placing them with a nonreceptive female (immature virgin females, decapitated mature virgin females, or mature mated females), termed as the courtship suppression/conditioning assay. Early studies showed that male flies that experience failure to mate upon interaction with nonreceptive previously mated females show decreased motivation to court (courtship suppression). Courtship suppression is an important experimental paradigm for studying genes and neuronal circuits that mediate short- and long-term memory. The anti-aphrodisiac male-specific pheromone 11-cis-vaccenyl-acetate plays a key role in this conditioned response, as male flies learn to associate its presence on mated females with the failure to mate.

Courtship inDrosophila melanogasterinvolves a series of innate, complex behaviors that allow male and female flies to exchange sensory information and assess the quality of a potential mate. Although highly robust and stereotypical, courtship behaviors can be modulated by internal state and experience. This protocol describes methods for designing and carrying out experiments that measure courtship performance in single-pair assays, in which a male is paired with a female, or in competitive assays, in which a male is presented with a female and with a male competitor. It also includes approaches for measuring female sexual receptivity during courtship.

Courtship behaviors inDrosophila melanogasterare innate and contain highly stereotyped but also experience- and state-dependent elements. They have been the subject of intense study for more than 100 years. The power ofDrosophilaas a genetic experimental system has allowed the dissection of reproductive behaviors at a molecular, cellular, and physiological level. As a result, we know a great deal about how flies perceive sensory cues from potential mates, how this information is integrated in higher brain centers to execute reproductive decisions, and how state and social contexts modulate these responses. The simplicity of the assay has allowed for its broad application. Here, we introduce methods for studying male and female innate reproductive behaviors as well as their plastic responses.

During reproduction, male and female flies use wing vibration to generate different acoustic signals. Males produce a courtship song before copulation that is easily recognized by unilateral wing vibration. In copula, females produce a distinct sound pattern (copulation song) with both wings. Sexual rejection of immature virgins and aggressive encounters between males are also accompanied by sound pulses generated by wing flicks. Fly song has frequency ranges audible to the human ear and can be directly listened to after appropriate amplification. When displayed in an oscillogram, audio recordings can be mapped on wing-movement patterns and thus provide a fast and precise method to sample and quantify motor behaviors with high temporal resolution. After recording different fly sounds, their effect on behavior can be tested in playback experiments.

Upon copulation, females undergo a switch-like change in their behavior and physiology, known as “postmating responses.” These strong behavioral and physiological changes are triggered by the transfer of male seminal proteins during copulation. Postmating response is associated with strong reduction in receptivity, indicated by the females kicking their legs toward the suitor and curving their abdomen downward to hide their genitalia from them and extruding their ovipositor at the tip of the abdomen, which physically prevents copulation. The transfer of male-specific pheromones, such as 11-cis-vaccenyl-acetate, during copulation further reduces female attractiveness. In addition, mated females exhibit increased ovulation, egg-laying behavior, enhanced feeding behavior, and changes in food preference. However, females increase their rate of remating when they are in social groups or in the presence of food. This protocol describes methods for measuring female postmating behaviors, such as oviposition, female sexual receptivity, and mating plug ejection.

Background: Lipid homeostasis is an evolutionarily conserved process that is crucial for energy production, storage and consumption. Drosophila larvae feed continuously to achieve the roughly 200-fold increase in size and accumulate sufficient reserves to provide all energy and nutrients necessary for the development of the adult fly. The mechanisms controlling this metabolic program are poorly understood. Results: Herein we identified a highly conserved gene, orsai (osi), as a key player in lipid metabolism in Drosophila. Lack of osi function in the larval fat body, the regulatory hub of lipid homeostasis, reduces lipid reserves and energy output, evidenced by decreased ATP production and increased ROS levels. Metabolic defects due to reduced Orsai (Osi) in time trigger defective food-seeking behavior and lethality. Further, we demonstrate that downregulation of Lipase 3, a fat body-specific lipase involved in lipid catabolism in response to starvation, rescues the reduced lipid droplet size associated with defective orsai. Finally, we show that osi-related phenotypes are rescued through the expression of its human ortholog ETFRF1/LYRm5, known to modulate the entry of β-oxidation products into the electron transport chain; moreover, knocking down electron transport flavoproteins EtfQ0 and walrus/ETFA rescues osi-related phenotypes, further supporting this mode of action. Conclusions: These findings suggest that Osi may act in concert with the ETF complex to coordinate lipid homeostasis in the fat body in response to stage-specific demands, supporting cellular functions that in turn result in an adaptive behavioral response.