Seminar

Cultural Transmission of Mating Preferences in Fruit Flies - Diving into Neurobiological Mechanisms

Sabine Noebel

October 22, 2019, 12:45–13:45

Toulouse

Room MS 003

IAST Lunch Seminar

Abstract

We recently showed that the social learning of mating preferences (i.e., mate-copying) in the fruit fly Drosophila melanogasterhas all the cognitive abilities that can lead to the emergence of persistent cultural traditions of preferring one male type over other types of males, which considerably broadens the taxonomic scope of the cultural process. Now, we are interested in the cognitive mechanisms of this social learning. Fruit flies have relatively small brains with ~100,000 neurons and many genes and molecular pathways are well conserved (signal transduction, neurotransmitters, etc.), which makes fruit flies an excellent model organism. Up to now, most studies focus on visual or olfactory individual learning and memory but not on social learning (mate-copying in our specific case). In aversive olfactory learning tasks, the protein Rutabaga was identified as a coincidence detector needing simultaneous inputs from two stimuli to be fully activated (in olfactory aversive learning electric shocks and an odour). A mate-copying experiment contains two phases: a demonstration where an observer female can watch a conspecific female (called demonstrator female) choosing between two males of contrasting phenotypes (artificially dusted with green or pink powders) for mating followed by a copulation test when the observer female can choose between a new green and pink male. Because we found that flies that are lacking Rutabaga do not perform mate-copying, we speculate that Rutabaga is also required in mate-copying to integrate the information of copulation and the colour of the male that copulated. To find out which brain parts are involved in social learning we used a Rutabaga-null mutant that is lacking Rutabaga and expressed it only in specific brain regions of interest. We expressed the wild-type Rutabaga protein specifically in the Central Complex (CC) that is known to be crucial to integrate information, learn visually and navigate, or in the mushroom body (MB) that is known to be involved in olfactory memory, context generalization and motor control. We show that specifically rescuing Rutabaga expression in the CC fails to rescue social learning, while rescuing it in the MBs fully rescues mate-copying, suggesting MBs are the main centre of this social learning integration. MBs consist of three distinct lobes (α, β, γ), each containing neurons with distinct roles. Thus, in a second step, we rescued Rutabaga in one of the lobes neurons at a time to localize what MBs neurons are required in this mate-copying. A full rescue of mate-copying was found when rescuing Rutabaga in γ-neurons, but not in other neurons. For long-term memory the situation is less clear for now. However, this is the first study showing the neuronal pathways required for social learning in a mate-choice context in an invertebrate and that the γ-neurons of MB are crucial in this task.