title: Cold adaptation shapes the robustness of metabolic networks in Drosophila melanogaster.
abstract: When ectotherms are exposed to low temperatures, they enter a cold-induced coma (chill coma) that prevents resource acquisition, mating, oviposition, and escape from predation. There is substantial variation in time taken to recover from chill coma both within and among species, and this variation is correlated with habitat temperatures such that insects from cold environments recover more quickly. This suggests an adaptive response, but the mechanisms underlying variation in recovery times are unknown, making it difficult to decisively test adaptive hypotheses. We use replicated lines of Drosophila melanogaster selected in the laboratory for fast (hardy) or slow (susceptible) chill-coma recovery times to investigate modifications to metabolic profiles associated with cold adaptation. We measured metabolite concentrations of flies before, during, and after cold exposure using nuclear magnetic resonance (NMR) spectroscopy to test the hypotheses that hardy flies maintain metabolic homeostasis better during cold exposure and recovery, and that their metabolic networks are more robust to cold-induced perturbations. The metabolites of cold-hardy flies were less cold responsive and their metabolic networks during cold exposure were more robust, supporting our hypotheses. Metabolites involved in membrane lipid synthesis, tryptophan metabolism, oxidative stress, energy balance, and proline metabolism were altered by selection on cold tolerance. We discuss the potential significance of these alterations.
authors.affiliation: Department of Integrative Biology, University of California, Berkeley, California 94720. cmw@berkeley.edu.
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Williams
authors.forename: Miki
authors.initials: M
authors.lastname: Watanabe
authors.forename: Mario R
authors.initials: MR
authors.lastname: Guarracino
authors.forename: Maria B
authors.initials: MB
authors.lastname: Ferraro
authors.forename: Arthur S
authors.initials: AS
authors.lastname: Edison
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Morgan
authors.forename: Arezue F B
authors.initials: AF
authors.lastname: Boroujerdi
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Hahn
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003080:Cold Temperature; D058639:Cold-Shock Response / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D004734:Energy Metabolism; D008563:Membrane Lipids / Q000378:metabolism; D055442:Metabolome; D018384:Oxidative Stress; D011392:Proline / Q000378:metabolism; D012641:Selection, Genetic; D014364:Tryptophan / Q000378:metabolism
chemical_list: D008563:Membrane Lipids; D014364:Tryptophan; D011392:Proline
keywords: Correlation networks; NMR-based metabolomics; energy balance; insect; thermal limits; winter