Or22 allelic variation alone does not explain differences in discrimination of yeast-produced volatiles by D. melanogaster

Abstract

Different lines of the fruit fly Drosophila melanogaster show variation in the ability to discriminate between volatiles produced by the yeast Saccharomyces cerevisiae under natural (nitrogen-limiting, YVN) or laboratory (sugar-limiting, YVL) conditions. Previous work in our laboratory uncovered a strong correlation between heightened sensitivity to YVN wild D. melanogaster lines that harbored a chimeric variant of the highly variable odorant receptor 22 (Or22) locus of D. melanogaster. We sought to determine if this trend held for an extended set of D. melanogaster lines, if observed variation within chimeric and non-chimeric lines could be explained by nucleotide polymorphisms and if replacing Or22 with a chimeric allele in a non-chimeric background could confer the enhanced ability to detect YVN. In parallel, we performed crosses of chimeric and non-chimeric fly lines and assayed the behavior of their progeny for enhanced sensitivity to YVN to assess the heritability of the Or22 locus. Ultimately, we found that, while the overall trend of increased sensitivity to YVN in chimeric lines persists, there are exceptions and variation that cannot be explained by sequence variation at the Or22 locus. In addition, we did not observe increased sensitivity for YVN upon replacing the Or22 allele in a non-chimeric line (OreR) with that from our most YVN-sensitive, chimeric line (ME). Though our results do not support our hypothesis that Or22 is the primary driver of sensitivity to YVN, Or22 remains an interesting locus in the context of fly-yeast ecology.