Variation in resistance and acclimation to low-temperature stress among three geographical strains of Drosophila melanogaster

Variation in cold resistance was examined in cold acclimated and non-acclimated Drosophila melanogaster from three geographical strains representing Morocco, France and Finland. Resistance was estimated as survival of adults at 0°C; the acclimation treatment involved a long-term exposure to 11°C starting from the late pupal stage and continuing with adults. After the cold stress, two fitness traits, percentage of fertile individuals and the number of adult progeny, were scored in both acclimated and non-acclimated flies. Acclimation dramatically increased survival in all strains, but did not affect the pattern of geographic variation in cold resistance. The European flies tended to be more resistant than the African ones and the ranking from most to least resistant strain was France>Finland>Morocco. In the absence of acclimation, females showed a higher survival than males. Percentage of fertile males in all strains and the number of progeny in the Finnish and French strains were decreased after acclimation. Without cold acclimation, the number of progeny was higher in the European flies as compared with the African ones. The results suggest that populations of D. melanogaster from cold climates are better adapted to low stressful temperatures and among-population variation in cold resistance may be due to non-plastic rather than plastic genetic changes. The deleterious effects of cold pretreatment on the life-history parameters indicate a possibility for acclimation costs in reproduction.