Postmating sexual interactions: behavioural, molecular and evolutionary aspects in Drosophila – SexDro

IIn organisms with sexual reproduction, mating success depends on two primary components: 1) finding and recognizing sexual partners and 2) female receptivity to males. These components are controlled by chemical signals, or pheromones, produced by both the male and female. These pheromones also impact mating success by directly influencing the time between two matings. The seminal pheromones transferred by the males during mating are responsible for physiological changes within females which reduce her receptivity thus increasing the male paternity insurance. Though these chemical signals are particularly crucial in insects, they have been poorly investigated so far. They are especially important since they trigger divergent interests between sexes and are then involved in sexual conflict : the reproductive output of males is maximized at the expense of females (considering her lifetime survival for example). The aim of this project is to study chemical signals involved in sexual reproduction, and their evolution. Our project will focus on a model insect - Drosophila melanogaster - as well as several closely related species exhibiting distinct sexual behaviours. The genomes of these species have been fully sequenced, and we can take advantage of a wide range of genetic and molecular tools already developed in D. melanogaster (notably 30000 transgenic RNAi lines which can be used to knock-down most of the identified genes). Our project involves two independent partners located in Gif-sur-Yvette who will work in tight collaboration and who are specialised in insect physiology and in the chemistry of natural compounds. Both partners have complementary technical and scientific expertises allowing a combination of genetic, biochemical and behavioural approaches while implementing a cutting edge chemical approach.
The first part of the project will deal with modification of female pheromones, following mating. These pheromones are long chain hydrocarbons produced by the tegument that make females attractive to males. In the second part we will study the male seminal compounds (lipid and peptide pheromones) that are transmitted to the female during copulation. These pheromones act on female receptivity and trigger important physiological changes.
Seminal fluid transferred to female results in inhibition of her receptivity. The duration of this inhibition is variable and determines the mating system (monoandry vs polyandry). We will analyse which components of seminal fluid influence the inhibition of receptivity. Seminal fluid is also thought to be responsible for the decrease in female cuticular pheromone which occurs after mating. The effects of these male sex pheromones transmitted to the female on the production of female pheromones will be tested along with their impact on mating system.
With regard to the male lipid pheromone, cVA, we will characterize biosynthetic enzymes to build mutants lacking of cVA and to study how they modify female physiology and behaviour. Likewise, we will consider the effect of male seminal peptides on female pheromone production and behaviour. Proteomic and molecular analyses will be performed to identify the seminal peptides (Acps, especially sex peptide Acp70A) from both monoandrous and polyandrous species within the melanogaster subgroup to identify the peptides responsible for modifying female reproductive behaviour. The effect of these peptides on inhibition of female receptivity will be tested in order to better understand the relationship between specific seminal peptides and mating patterns. Our final objective is to identify and characterise the key chemical signals that determine insect reproductive success. This work will also provide data on the evolution of these signals and their role in reproductive isolation and speciation. The outcome of this research could lead to new strategies to control populations of pest insects for agriculture or insect vectors of human diseases.