Abstract
In insects, many critical olfactory behaviours are mediated by the large odorant receptor (Or) gene family, which determines the response properties of different classes of olfactory receptor neurons (ORNs). While ORN responses are generally conserved within and between Drosophila species, variant alleles of the D. melanogaster Or22 locus have previously been shown to alter the response profile of an ORN class called ab3A. These alleles show potential clinal variation, suggesting that selection is acting at this locus. Here, we investigated if the changes seen in ab3A responses lead to changes in olfactory-related behaviours. We show that variation at the Or22 locus and in the ab3A neurons are not fully compensated for by other ORNs and lead to overall changes in antennal odorant detection. We further show that this correlates with differences in odorant preference behaviour and with differences in oviposition site preference, with flies that have the chimaeric short allele strongly preferring to oviposit on banana. These findings indicate that variation at the Or22 locus leads to changes in olfactory-driven behaviours, and add support to the idea that the ab3A neurons are of especial importance to the ecology of Drosophila flies.
Highlights
Animals rely on their sense of smell to discriminate between odours in order to identify and locate mates, dangers and food sources
If not all, of the odorants detected by ab3A neurons are detected by other olfactory receptor neurons (ORNs), for example, pentyl acetate is detected by ab1A, ab5B, ab6A and ab7A neurons, and ethyl butanoate is detected by ab1A, ab8A, ab8B, ab10A, ab3B and ab2B neurons [1,9]
Our data suggest that ab3A response variation due to changes at the D. melanogaster Or22 locus is associated with differences in two different olfactory-driven behaviours
Summary
Animals rely on their sense of smell to discriminate between odours in order to identify and locate mates, dangers and food sources. Flying insects need to be able to do all of this rapidly, and use their chemosensory systems to identify the optimal places to lay their eggs. Odour identity is combinatorially encoded through the inputs from a large number of classes of olfactory receptor neurons (ORNs) [1,2,3], whose responses are determined by the olfactory receptors they express [4,5,6]. One of the major families of olfactory receptors in insects is the rapidly evolving Or gene family, which encode highly divergent ligand-gated ion channels and primarily detect volatile odorants [7]. In D. melanogaster, individual Ors/ORNs can be either broadly tuned (responding strongly to a wide range of odorants) or narrowly tuned (responding strongly to one or a few odorants), albeit with there being a continuum in the breadth of tuning rather than a strict dichotomy [8,9]
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