SELECTION FOR HEAT-SHOCK RESISTANCE IN LARVAL AND IN ADULT DROSOPHILA-BUZZATTII - COMPARING DIRECT AND INDIRECT RESPONSES

Direct and correlated responses in selection for heat-shock resistance in adult and in larval Drosophila buzzatii were studied. Two lines we re artificially selected for higher survival to heat stress as adults, and two other lines were reared under a fluctuating thermal environme nt as larvae, 35 degrees C for 6 h and 25 degrees C for 18 h, to ''nat urally'' select for higher resistance as larvae. The latter two lines were duplicated after nine generations to yield additional lines to be ''naturally'' selected as larvae at a higher temperature, 38.2 degree s C for 6 h. Control lines were maintained separately for the adult an d larval selection lines. A significant direct response to selection w as found for the adult selection lines. However, larvae of these adult selection lines were no more heat resistant than were larvae of the c ontrol lines. One of the two larval selection lines increased signific antly in heat resistance as larvae. However adult heat resistance was similar for lines selected as larvae and the corresponding control lin es maintained at 25 degrees C. Changes in developmental time accompani ed changes in survival after stress in both sets of lines selected for increased heat resistance.