Abstract
Oviposition is a female-specific behavior that directly affects fecundity, and therefore fitness. If a fertilized female encounters another male that she has evaluated to be of better quality than her previous mate, it would be beneficial for her to remate with this male rather than depositing her eggs. Females who decided not to remate exhibited rejection behavior toward a courting male and engaged in oviposition. Although recent studies of Drosophila melanogaster identified sensory neurons and putative second-order ascending interneurons that mediate uterine afferents affecting female reproductive behavior, little is known about the brain circuitry that selectively activates rejection versus oviposition behaviors. We identified the sexually dimorphic pC2l and female-specific pMN2 neurons, two distinct classes of doublesex (dsx)-expressing neurons that can initiate ovipositor extension associated with rejection and oviposition behavior, respectively. pC2l interneurons, which induce ovipositor extrusion for rejection in females, have homologues that control courtship behavior in males. Activation of these two classes of neurons appears to be mutually exclusive and each governs hierarchical control of the motor program in the VNC either for rejection or oviposition, contributing centrally to the switching on or off of the alternative motor programs.
Highlights
Mating and oviposition are two major activities that affect the fitness of adult female insects
We demonstrated, by means of clonal manipulation of brain neurons, that apparently similar ovipositor extensions in these two behaviors are initiated by distinct classes of dsx-GAL4 neurons in the brain, pC2l for mating-type extrusion in response to male courtship and pMN2 for oviposition in mated females
PC2l is the first brain neuron identified as involved in the regulation of extrusion in female mating behavior. pC2l is a sexually dimorphic neural cluster with dsx-GAL4 expression, and its counterpart in males plays an important role in executing male courtship behavior
Summary
Mating and oviposition are two major activities that affect the fitness of adult female insects. Mating is a prerequisite for laying fertilized eggs, yet inappropriate mating by fertilized females may reduce their fecundity. The inseminated female who has made decision not to mate again will display post-mating behaviors, i.e., rejection behavior toward the second male and depositing of eggs upon finding an appropriate oviposition site. The female post-mating behaviors are believed to rely on a hard-wired neural system that is postulated to integrate a variety of neural inputs which encode both internal and external information and which activate the neural center for either rejection or oviposition [1]. Any higher-order neurons that may be involved in this circuitry and their connectivity remain largely elusive, because studying neural circuits at the single cell level is technically demanding.
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