QTL for the thermotolerance effect of heat hardening, knockdown resistance to heat and chill-coma recovery in an intercontinental set of recombinant inbred lines of Drosophila melanogaster

FABIAN M. NORRY; ALEJANDRA C. SCANNAPIECO; PABLO SAMBUCETTI; CARLOS I. BERTOLI; VOLKER LOESCHCKE

MOLECULAR ECOLOGY

Blackwell Publishing Ltd

Año: 2008 p. 4570 - 4581

0962-1083

AbstractThe thermotolerance effect of heat hardening (also called short-term acclimation), knockdownresistance to high temperature (KRHT) with and without heat hardening and chill-comarecovery (CCR) are important phenotypes of thermal adaptation in insects and other organisms.Drosophila melanogaster from Denmark and Australia were previously selected for lowand high KRHT, respectively. These flies were crossed to construct recombinant inbredlines (RIL). KRHT was higher in heat-hardened than in nonhardened RIL. We quantify theheat-hardening effect (HHE) as the ratio in KRHT between heat-hardened and nonhardenedRIL. Composite interval mapping revealed a more complex genetic architecture for KRHTwithout heat-hardening than for KRHT in heat-hardened insects. Five quantitative trait loci(QTL) were found for KRHT, but only two of them were significant after heat hardening.KRHT and CCR showed trade-off associations for QTL both in the middle of chromosome2 and the right arm of chromosome 3, which should be the result of either pleiotropy or linkage.The major QTL on chromosome 2 explained 18% and 27–33% of the phenotypic variance inCCR and KRHT in nonhardened flies, respectively, but its KRHT effects decreased by heathardening. We discuss candidate loci for each QTL. One HHE-QTL was found in the regionof small heat-shock protein genes. However, HHE-QTL explained only a small fraction ofthe phenotypic variance. Most heat-resistance QTL did not colocalize with CCR-QTL.Large-effect QTL for CCR and KRHT without hardening (basal thermotolerance) were consistentacross continents, with apparent transgressive segregation for CCR. HHE (induciblethermotolerance) was not regulated by large-effect QTL.Keywords: cold stress, heat acclimation, inducible thermotolerance, thermal adaptation, trade-off,transgressive segregationReceived 10 June 2008; revision received 6 August 2008; accepted 20 August 2008