HEAT-SHOCK TOLERANCE AND INBREEDING IN DROSOPHILA-BUZZATII

The effect of inbreeding on survival after a short-term heat shock was tested for two age groups of the cactophilic fruit fly, Drosophila bu zzatii, reared under nonstress conditions. Four inbreeding levels (F = 0, F = 0.25, F = 0.375, F = 0.5) were generated by outcrossing or ful l-sib mating. All flies were conditioned at 36.5 degrees C for 75 min prior to exposure to stress, to activate the synthesis of heat-shock p roteins. These proteins are known to protect cells against stress dama ge. The younger group of flies were exposed to a thermal stress of 40. 7 degrees C for 88 min, 103 min, or 118 min and the older flies to the same temperature only for 88 min or 103 min, as the survival of older flies after heat stress was much lower than that of the younger flies . Survival after heat shock declined with increased inbreeding in both age groups. For the younger flies, the slope of the regression line, F, on survival was lower at higher stress levels. For the older flies, inbreeding effects were similar at both stress levels. Mortality with out stress also differed significantly among inbreeding groups, mainly because of a large difference between the F = 0.5 group and all other s.