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D. simulans vs. Sechellia adult bodies choice vs. no choice -DGRC Two Colour arrays with Dye Swapping

ABSTRACT: Here we show that Drosophila sechellia—a specialist on the fruit of Morinda citrifolia that recently diverged from its generalist sister-species, D. simulans—has rapidly accumulated loss-of-function alleles and reduced gene expression at genes affecting olfaction, detoxification, and metabolism. While D. sechellia increases expression of genes involved with oogenesis and fatty acid metabolism when on its host, many more genes show reduced expression in D. sechellia. For several functionally related genes, this decrease in expression is associated with loss-of-function alleles. The rapid accumulation of these alleles potentially affected D. sechellia’s initial adaptation to M. citrifolia, likely contributes to D. sechellia’s poor competitive ability off of its host, and increases ecological isolation between D. sechellia and its sister species. Our results suggest that a subset of genes reduce or lose function as a consequence of host specialization, which may explain why, in general, specialist insects tend to shift to chemically similar hosts. Moreover, if the accumulation of non- or weakly functional genes in a specialist enhances the ecological isolation between it and other species, then this process may explain why specialists are speciose. Keywords: comparative hybridization, gene expression

ORGANISM(S): Drosophila simulans Drosophila sechellia Drosophila melanogaster

PROVIDER: GSE13789 | GEO | 2008/12/03

SECONDARY ACCESSION(S): PRJNA110543

REPOSITORIES: GEO

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Project description:The underlying genetic basis of adaptive phenotypic changes are generally poorly understood, yet a growing number of case studies are beginning to shed light on important questions about the molecular nature and pleiotropy of such changes. We use Drosophila sechellia, a dietary specialist fruit fly that has evolved to specialize on a single toxic host plant: Morinda citrifolia, as a model for adaptive phenotypic change and seek to determine the genetic basis of traits associated with host specialization in this species. The fruit of M. citrifolia is toxic to other Drosophilids, primarily due to high levels of the defense chemical octanoic acid (OA) yet D. sechellia has evolved resistance to OA. Our prior work identified three Osiris family genes that reside in a fine-mapped QTL for OA resistance: Osiris 6 (Osi6), Osi7, and Osi8, that can alter OA resistance in adult D. melanogaster when knocked-down with RNA interference (RNAi) suggesting they may contribute to OA resistance in D. sechellia. Genetic mapping identified overlapping genomic regions involved in larval and adult OA resistance in D. sechellia, yet it remains unknown whether Osiris genes contribute to resistance in both life stages. Furthermore, because multiple genomic regions contribute to OA resistance, we aim to identify other gene(s) involved in this adaptation. Here, we identify candidate larval OA resistance genes using RNA-sequencing to measure genome-wide differential gene expression in D. sechellia larvae after exposure to OA and functionally test identified genes for a role in OA resistance. We then test the Osiris genes previously shown to alter adult OA resistance for effects on OA resistance in larvae. While the genes identified by RNA-seq we tested in larvae thus far do not influence OA resistance, we found that Osi8 knockdown decreased OA resistance in D. melanogaster larvae. These data suggest that evolved changes in Osi8 could impact OA resistance in multiple life stages while Osi6 and Osi7 may only impact adult resistance to OA.

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D. simulans vs. Sechellia adult bodies choice vs. no choice -DGRC Two Colour arrays with Dye Swapping

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