The smell of love in Drosophila

Abstract

Odors are key sensory signals for social communication and food search in animals including insects. Drosophila melanogaster, is a powerful neurogenetic model commonly used to reveal molecular and cellular mechanisms involved in odorant detection. Males use olfaction together with other sensory modalities to find their mates. Here, we review known olfactory signals, their related olfactory receptors, and the corresponding neuronal architecture impacting courtship. OR67d receptor detects 11-cis-Vaccenyl Acetate (cVA), a male specific pheromone transferred to the female during copulation. Transferred cVA is able to reduce female attractiveness for other males after mating, and is also suspected to decrease male-male courtship. cVA can also serve as an aggregation signal, maybe through another OR. OR47b was shown to be activated by fly odors, and to enhance courtship depending on taste pheromones. IR84a detects phenylacetic acid (PAA) and phenylacetaldehyde (PA). These two odors are not pheromones produced by flies, but are present in various fly food sources. PAA enhances male courtship, acting as a food aphrodisiac. Drosophila males have thus developed complementary olfactory strategies to help them to select their mates.

Keywords: Drosophila; courtship; nervous system; olfaction; receptor.

Figure 1

Olfactory perception in Drosophila. (A) Olfactory signals are detected through the maxillary palps (MP) and the 3rd antennal segment (IIIAS). (B) OSNs (light green) project to the antennal lobe (AL), where the signal is transferred to projection neurons (dark green) targeting the mushroom bodies (MB) and to the lateral horn (LH).

Figure 2

Olfactory pathways influencing courtship. (A) The only known repressing olfactory signal comes from cVA (red circle, present into male, and into mated female sex-organs; Farine et al., 2012), which is detected by OR67d. LUSH is an odorant binding protein (OBP), which interacts with Sensory neuron membrane protein (SNMP), to activate OR67d. OSNs expressing OR67d project to the DA1 glomerulus in the AL. The olfactory information is then transferred to projection neurons targeting the MB (in the calyx region, CA), and the LH. (B) Enhancing signals (present on the flies such as virgin females) stimulate either OR47b (with an unknown odorant, dark green triangle), or IR84a (with PAA, light green square). OR47b OSNs target the VA1v glomerulus, and IR84a OSNs VL2a. Projection neurons emerging from these three AL glomeruli project into a specific area of the LH (doted circle). Symbols: ♂ for male, ♀ for mated female, for virgin female.