Natural variation at the Drosophila melanogaster Or22 odorant receptor locus is associated with changes in olfactory behaviour

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.

Natural variation at the Drosophila melanogaster Or22 odorant receptor locus is associated with changes in olfactory behaviour

In insects many critical olfactory behaviours are mediated by the large odorant receptor (Or) gene family, which determine 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 the response profiles 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 that could be under selective pressure, and add support to the idea that the ab3A neurons are of especial importance to the ecology of Drosophila flies.

Drosophila suzukii avoidance of microbes in oviposition choice

While the majority of Drosophila species lays eggs onto fermented fruits, females of Drosophila suzukii pierce the skin and lay eggs into ripening fruits using their serrated ovipositors. The changes of oviposition site preference must have accompanied this niche exploitation. In this study, we established an oviposition assay to investigate the effects of commensal microbes deposited by conspecific and heterospecific individuals and showed that the presence of microbes on the oviposition substrate enhances egg laying of Drosophila melanogaster and Drosophila biarmipes , but discourages that of D. suzukii . This result suggests that a drastic change has taken place in the lineage leading to D. suzukii in how females respond to chemical cues produced by microbes. We also found that hardness of the substrate, resembling that of either ripening or damaged and fermenting fruits, affects the response to microbial growth, indicating that mechanosensory stimuli interact with chemosensory-guided decisions to select or avoid oviposition sites.

Drosophila suzukii avoidance of microbes in oviposition choice

While the majority of Drosophila species lay eggs onto fermented fruits, females of D. suzukii pierce the skin and lay eggs into ripening fruits using their serrated ovipositors. The changes of oviposition site preference must have accompanied this niche exploitation. In this study, we established an oviposition assay to investigate the effects of commensal microbes deposited by conspecific and heterospecific individuals, and showed that presence of microbes on the oviposition substrate enhances egg-laying of D. melanogaster and D. biarmipes, but discourages that of D. suzukii. This result suggests that a drastic change has taken place in the lineage leading to D. suzukii in how females respond to chemical cues produced by microbes. We also found that hardness of the substrate affects the response to microbial growth, indicating that mechanosensory stimuli interact with chemosensory invoked decisions to select or avoid oviposition sites.