Title : 1 2 Natural variation at the Drosophila melanogaster Or 22 odorant receptor locus is 3 associated with changes in olfactory behaviour 4 5 6 7

34 In insects many critical olfactory behaviours are mediated by the large odorant receptor (Or) 35 gene family, which determine the response properties of different classes of olfactory receptor 36 neurons (ORNs). While ORN responses are generally conserved within and between 37 Drosophila species, variant alleles of the D.melanogaster Or22 locus have previously been 38 shown to the response profiles of an ORN class called ab3A. These alleles show potential clinal 39 variation, suggesting that selection is acting at this locus. Here, we investigated if the changes 40 seen in ab3A responses lead to changes in olfactory-related behaviours. We show that variation 41 at the Or22 locus and in the ab3A neurons are not fully compensated for by other ORNs and 42 lead to overall changes in antennal odorant detection. We further show that this correlates with 43 differences in odorant preference behaviour and with differences in oviposition site preference, 44 with flies that have the chimaeric short allele strongly preferring to oviposit on banana. These 45 findings indicate that variation at the Or22 locus leads to changes in olfactory-driven 46 behaviours that could be under selective pressure, and add support to the idea that the ab3A 47 neurons are of especial importance to the ecology of Drosophila flies. 48 49 50