The evolution of mechanosensory perception in the context of oviposition site choice in Drosophila

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Animal diversity is manifest, not only in the seemingly infinite variations of their morphology, but also in the variety of their innate behaviors. While our understanding of morphological variation takes the form of genetic principles today, our understanding of behavior evolution is lagging far behind. For this reason, my group as recently set up a simple paradigm to examine the genetic and neuronal changes underlying a simple change in behavior. We are studying how a female fly choses a suitable site to lay her eggs. We found that this key reproductive decision is made differently by closely related species of Drosophila with different ecologies. All species we have examined are akin to the model species D. melanogaster and use their sense of touch to probe substrate suitability for their eggs. Yet, their preferences for substrate stiffness have changed. In particular, the invasive pest species D. suzukii hardly choses between substrates of different stiffness, unless the difference is equivalent to that of a green strawberry vs. a ripe strawberry. By contrast, D. melanogaster proves extremely choosy, and prefers the stiffness equivalent to that of a rotten fruit over that of a very ripe fruit. In a first project, we want to dissect how a female fly (D. melanogaster) senses and selects substrate stiffness at the genetic and neuronal levels. We will elaborate on recent finding that have identified a key gene in this process, to decipher how and in which neurons this gene is used, and where these primary neurons dispatch the sensory information. We will take advantage of the abundant ressources available for Drosophila melanogaster neurogenetics. In a second project, we want to understand how the egg-laying substrate preferences have evolved. We will first focus on single flies of different species with different preferences, and describe their behavior quantitatively to understand how they operate their choice. We will then ask if the key gene for the choice behavior mentioned above, has itself accumulated changes in its coding sequence or in its regulation explaining the change of behavior. Finally, we will search for possible changes in the primary sensory neurons mediating the choice, by comparing their anatomy and by manipulating the key gene between species (exchanging alleles). Together, these 2 projects will provide an overview of the neurogenetics underlying a mechanosensory preference, and the evolution of this preference.