Mating-Induced Behavioral Changes in Female Drosophila Are Modulated by Serotonin

Mating influences the physiology of female animals and induces changes in behaviors associated with securing resources for their offspring. Modulatory neurotransmitters are known to adjust behavioral responses of animals according to environmental cues and internal physiological states. In that regard, it has been shown that serotonin (5-HT) modulates some post-mating behavioral features in Drosophila. However, it remains unknown whether serotonin regulates post-mating social behavior or responses to food cues in flies, which are among several behaviors that serve to secure their survival and reproduction. Here, we report a behavioral paradigm, the yeast-response test (YRT), for exploring locomotor and social behavioral changes in groups of virgin and mated females using yeast odor as a naturalistic food signal. Using this setup, we found that exposure to yeast odor increases social interactions in mated but not virgin females under non-aversive conditions and that these responses are suppressed at aversive temperatures. Furthermore, chronic impairment of serotonin transporter function reverses the social behavioral response to food odor in mated females, without affecting their olfactory capacity. Whole-brain 5-HT content, as well as histone serotonylation, were unchanged between virgin and mated females, suggesting that 5-HT contribution to these changes is mediated at a circuit level rather than by global neuromodulatory mechanisms. Consistent with this idea, silencing serotonin projection neurons (SPNs) selectively abolished mating-induced changes in social behavior without affecting the locomotor effects. These results provide further support for data in the literature showing that SPNs belong to a discrete circuit underlying social behaviors in female flies. Together, these results support a model in which serotonergic signaling shapes post-mating behavior in Drosophila through functionally segregated neural circuits.