title: Genetic basis of octanoic acid resistance in Drosophila sechellia: functional analysis of a fine-mapped region.
abstract: Drosophila sechellia is a species of fruit fly endemic to the Seychelles islands. Unlike its generalist sister species, D. sechellia has evolved to be a specialist on the host plant Morinda citrifolia. This specialization is interesting because the plant's fruit contains secondary defence compounds, primarily octanoic acid (OA), that are lethal to most other Drosophilids. Although ecological and behavioural adaptations to this toxic fruit are known, the genetic basis for evolutionary changes in OA resistance is not. Prior work showed that a genomic region on chromosome 3R containing 18 genes has the greatest contribution to differences in OA resistance between D. sechellia and D. simulans. To determine which gene(s) in this region might be involved in the evolutionary change in OA resistance, we knocked down expression of each gene in this region in D. melanogaster with RNA interference (RNAi) (i) ubiquitously throughout development, (ii) during only the adult stage and (iii) within specific tissues. We identified three neighbouring genes in the Osiris family, Osiris 6 (Osi6), Osi7 and Osi8, that led to decreased OA resistance when ubiquitously knocked down. Tissue-specific RNAi, however, showed that decreasing expression of Osi6 and Osi7 specifically in the fat body and/or salivary glands increased OA resistance. Gene expression analyses of Osi6 and Osi7 revealed that while standing levels of expression are higher in D. sechellia, Osi6 expression is significantly downregulated in salivary glands in response to OA exposure, suggesting that evolved tissue-specific environmental plasticity of Osi6 expression may be responsible for OA resistance in D. sechellia.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Andrade López
authors.affiliation: Department of Biology, Wesleyan University, Middletown, CT, 06459, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Lanno
authors.affiliation: Department of Biology, Wesleyan University, Middletown, CT, 06459, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Auerbach
authors.affiliation: Department of Biology, Wesleyan University, Middletown, CT, 06459, USA.
authors.forename: E C
authors.initials: EC
authors.lastname: Moskowitz
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Sligar
authors.affiliation: Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA.|Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Wittkopp
authors.affiliation: Department of Biology, Wesleyan University, Middletown, CT, 06459, USA.|Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: J D
authors.identifier: http://orcid.org/0000-0003-1591-9418
authors.initials: JD
authors.lastname: Coolon
mesh_terms: D000818:Animals; D002210:Caprylates; D004330:Drosophila / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics*; D055785:Gene Knockdown Techniques; D034622:RNA Interference; D012469:Salivary Glands; D012750:Seychelles; D013045:Species Specificity
chemical_list: D002210:Caprylates; D029721:Drosophila Proteins; C031492:octanoic acid
keywords: adaptation; ecological genetics; insects; molecular evolution; species interactions