Social-sexual Modulation of Sperm Ejection

Abstract

Drosophila melanogaster females store sperm for about an hour after mating, and then remove the un-stored sperm along with the mating plug in a behavior called sperm ejection. The ejaculate holding period (EHP) is the period from the end of mating to sperm ejection, which affects sperm storage and fertility. In this study, I investigated whether and how the social-sexual context females experience after mating modulate EHP. After mating, female Drosophila kept with an actively courting male show a much shorter EHP than females left alone or with conspecific virgin females. This phenomenon was referred to as male-induced EHP shortening (MIES). The smell-blind Orco-deficient mutant females display no MIES, suggesting a role for olfactory receptor neurons (ORNs). MIES is also not observed in females in which Or47b-expressing neurons are silenced or lack Or47b gene expression. Restoring Orco expression in Or47b ORNs from Orco-deficient females also restore MIES. Moreover, using a comparative approach, I found that a pheromone in D. melanogaster male, 2-methyltetracosane (2MC), induces EHP shortening in females left alone after mating. Single sensillum recording showed that 2MC activates Or47b neurons. Activity of 2MC in females also requires either Or47b expression or Orco expression in Or47b ORNs. In addition to the Or47b ORNs located in the antenna, ppk23-positive gustatory receptor neurons (GRNs) in the tarsi, which are known to sense the major cuticular hydrocarbons 7-Tricosene and 7,11-Heptacosadiene, are also responsible for MIES. I also found that brain neurons such as octopaminergic OA-VPM3 and OA-VPM4, doublesex-positive pC1 neurons and pC1 downstream Drosulfakinin (Dsk) positive DSK-MP1B neurons regulates EHP. I used the hemibrain, a high-resolution electron microscopy connectome database, to map neural circuits connecting Or47b-positive ORNs or ppk23-positive GRNs with brain neurons, OA-VPM3, OA-VPM4, pC1 neurons and DSK-MP1B neurons. Combining neurogenetic, connectomic, and behavioral approaches, I uncovered neural circuit mechanisms that regulate timing of sperm ejection or EHP by integrating sensory cues that reflect social and sexual context.