PhD defence Nicolas Doubovetzky
Neurogenetic dissection of a sexual conflict in Drosophila melanogaster
Sexual conflict arises when males and females have opposing reproductive interests, driving the evolution of strategies to manipulate or resist each other. In Drosophila melanogaster, ejaculate ejection is a key trait in this conflict: females can eject the mating plug and ejaculate to regain attractiveness while males transfer Sex-Peptide, which delays ejection. This thesis investigates the neural, functional, and sensory mechanisms underlying this reproductive interaction. First, manipulation of female neurons revealed that doublesex-expressing neuronal populations contribute to ejaculate ejection. Further intersectional manipulations identified candidate neuronal populations through which Sex Peptide and its receptor modulate ejection timing, revealing a complex regulatory network rather than a simple stimulus–response pathway. Second, behavioural experiments demonstrated that females adjust ejaculate ejection and sperm storage according to the identity of males encountered after mating. These changes influence the relative representation of sperm from successive mates and subsequent paternity, providing evidence for cryptic female choice. a female-mediated processes that bias reproductive success after mating. Finally, sensory manipulations showed that this behavioural response depends on olfactory signaling. Experiments identified male-derived chemical cues, including heptanal and cis-vaccenyl acetate, whose combination produces a stronger response than either compound alone. Manipulation of candidate olfactory receptors further implicated OR22a and OR35a expressing pathways, with additional contributions from pathways associated with 1-cis-Vaccenyl acetate detection. Remarkably, pheromonal exposure alone can alter sperm storage without direct male interaction. Together, these findings connect neuronal circuit, chemical clues, and sperm allocation, providing mechanistic insight into cryptic female choice and the ongoing sexual conflict over reproductive success.