Genetic variation for egg-to-adult survival in drosophila melanogaster in a set of recombinant inbred lines reared under heat stress in a natural thermal environment

Abstract

Quantitative trait loci (QTL) for thermotolerance were previously identified for adult flies in several mapping populations of Drosophila melanogaster Meigen (Diptera: Drosophilidae) in the laboratory. However, laboratory assays may not necessarily reflect the performance under heat stress in the field. For instance, do the heat-resistance QTL regions in the field match the QTL for thermotolerance in laboratory studies? To address this and related questions we used a set of recombinant inbred lines (RIL), which were originally used to identify QTL in the laboratory.We tested egg-to-adult survival (EAS) QTL in a field experiment under naturally varying heat-stress temperatures in fly cultures reared on a rotting fruit (banana) in summer. EAS under heat stress was found to be 3–69lower (depending on RIL) in the field than in the corresponding control at benign temperature (25 °C). Five QTL for EAS were significant in the field experiment under heat stress, four of them co-located with plasticity QTL, and none of theQTL was significant at control temperature. All significant QTL overlapped (co-localized) with thermotolerance QTL previously identified in the laboratory. A previously found QTL in the middle of chromosome 2 explained near 30% of the phenotypic variance in EAS under heat stress in previous studies in the laboratory, but this QTL explained only 8% of the EAS variation in our field assay. The largest effect on EAS was found for an X-linked QTL (cytological range 7B3-10C3) in the heat-stress field experiment, explaining a high percentage (14–45%) of the phenotypic variation in EAS. The ecological relevance ofQTL implicated in this study is discussed.