The importance of increasing brain complexity for the evolution of novel social behaviors.

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Sexual conflict (SC) shapes the evolution of reproductive behaviours. It manifests itself in male traits that limit female reproductive choices, generating selection for female counter-adaptations. Evolutionary biologists proposed that SC causes cycles of adaptation-counteradaptation producing complex sexual interactions with little purpose other than stimulatory effectiveness. This is of interest for studies of the neuronal circuit underlying sexual behaviours because it suggests that those circuits have not only evolved for stimulus–response but also have layers of modulation resulting from their hijacking by the other sex. This project will test this hypothesis in Drosophila melanogaster, where SC is well documented and cutting-edge neurogenetic tools allow functional neuronal circuit dissection. Our data indicate that female neurons can advance female ejaculate ejection, a behaviour preparing females for remating. An unidentified population of these neurons are targeted by the male seminal fluid peptides to delay ejaculate ejection, showing hijacking of the neuronal circuit for sperm ejection instead of a stimulus-response. I will use intersectional genetic tools combined with optogenetics and RNA interference to define the female neurons that are targeted by male sex peptide. To define the stimulus-response part of the circuit, I will identify female sensory receptors that detect the presence of males and advance ejaculate ejection, using candidate gene and transcriptomics approach. By dissecting a neuronal circuit that has evolved under SC, I will test the hypothetical impact of SC on generating brain complexity.