Journal of Insect Physiology 54 (2008) 619–629 Effects of acclimation temperature on thermal tolerance and membrane phospholipid composition in the fruit fly Drosophila melanogaster Johannes Overgaard a,Ã , Alesˇ Tomcˇala b,d , Jesper G. Sørensen c , Martin Holmstrup a , Paul Henning Krogh a , Petr S ˇ imek b , Vladimir Kosˇta´l b,d a Department of Terrestrial Ecology, National Environmental Research Institute, University of Aarhus, Vejlsøvej 25, P.O. Box 314, DK-8600 Silkeborg, Denmark b Biology Centre AS CR, Institute of Entomology, C ˇ eske´Budeˇjovice, Czech Republic c Genetics and Ecology, Department of Biological Sciences, University of Aarhus, Aarhus C, Denmark d University of South Bohemia, Faculty of Science, C ˇ eske´Budeˇjovice, Czech Republic Received 23 October 2007; received in revised form 28 December 2007; accepted 31 December 2007 Abstract Adaptative responses of ectothermic organisms to thermal variation typically involve the reorganization of membrane glyceropho- spholipids (GPLs) to maintain membrane function. We investigated how acclimation at 15, 20 and 25 1C during preimaginal development influences the thermal tolerance and the composition of membrane GPLs in adult Drosophila melanogaster. Long-term cold survival was significantly improved by low acclimation temperature. After 60 h at 0 1C, more than 80% of the 15 1C-acclimated flies survived while none of the 25 1C-acclimated flies survived. Cold shock tolerance (1 h at subzero temperatures) was also slightly better in the cold acclimated flies. LT50 shifted down by ca 1.5 1C in 15 1C-acclimated flies in comparison to those acclimated at 25 1C. In contrast, heat tolerance was not influenced by acclimation temperature. Low temperature acclimation was associated with the increase in proportion of ethanolamine (from 52.7% to 58.5% in 25 1C-acclimated versus 15 1C-acclimated flies, respectively) at the expense of choline in GPLs. Relatively small, but statistically significant changes in lipid molecular composition were observed with decreasing acclimation temperature. In particular, the proportions of glycerophosphoethanolamines with linoleic acid (18:2) at the sn-2 position increased. No overall change in the degree of fatty acid unsaturation was observed. Thus, cold tolerance but not heat tolerance was influenced by preimaginal acclimation temperature and correlated with the changes in GPL composition in membranes of adult D. melanogaster. r 2008 Elsevier Ltd. All rights reserved. Keywords: Homeoviscous adaptation; Membrane phospholipid; PE; PC; Insect; Cold acclimation; Chilling injury 1. Introduction Ambient temperature impinges on virtually all biochem- ical and physiological processes in ectothermic animals and it is therefore one of the most important environmental factors dictating their survival and dispersal (Cossins and Bowler, 1987). This is certainly also true for insects that have evolved a range of behavioural, physiological and biochemical adaptations to endure exposure to seasonal and acute thermal fluctuations. In general, cold tolerant insects are broadly classified as being either freeze tolerant or freeze avoiding, but in reality many insects die at temperatures far above the temperature of crystallization of their body fluids so they do not possess any tolerance to low temperatures at all (Zachariassen, 1985; Lee, 1991; Bale, 1993; Sinclair et al., 2003). For example, the fruit fly, Drosophila melanogaster, is susceptible to chill injury at temperatures well above those causing freezing (Czajka and Lee, 1990). Such chill injury is thought to be associated with mismatching among various metabolic pathways (Knight et al., 1986); production of free radicals (Rojas and Leopold, 1996); disturbance of ion homeostasis (Kosˇta´l et al., 2004, 2006, 2007) and changes in the phase ARTICLE IN PRESS www.elsevier.com/locate/jinsphys 0022-1910/$ - see front matter r 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2007.12.011 Ã Corresponding author. Tel.: +45 89 42 26 48; fax: +45 89 42 25 86. E-mail address: biojo@biology.au.dk (J. Overgaard).