Speaker
Description
Living beings are not isolated and interact with each other. These interactions are often mediated by chemical odorants but how the evolution of the olfactory system can determine intra- and inter-specific interactions remains unclear. A peculiar example is the queen mandibular pheromone (QMP) in Apis mellifera, which inhibits the development of the ovaries in the conspecific workers (hence leading to social cohesion) and also in other insect species (hence protecting the colony). Of the different parasites of Apis, only one, the blind and wingless bee louse (Braula coeca), paradoxically spends its entire life cycle as an inquiline in the colony, clinging to the thorax or head of bees, with a clear preference for the queen at the end of the summer. We have sequenced its genome and confirmed that it is a basal branch of the Drosophilidae family, closely related to Drosophila melanogaster. To understand how Braula coeca has found an evolutionary means of circumventing the anti-ovarian effect of QMP, we investigated the evolution of multiple chemosensory gene families. We found the bee louse has lost almost half of the olfactory receptor drosophilid repertoire, including some that respond to QMPs in D. melanogaster. By combining multiple functional approaches, including behavioral assays in the field, electroantennography, heterologous gene expression of Braula receptors in D. melanogaster empty neurons, and CRISPR-Cas9 genome editing to induce B. coeca mutations in D. melanogaster, we are currently testing the hypothesis that the rapid evolution of Braula coeca's ORs has protected it from the anti-ovarian effects of QMP, enabling it to reproduce in an essentially sterilizing environment. Primary results are supporting this hypothesis, hence providing significant insights on how changes in chemosensory genes promote the evolution of inter-specific interactions.
