SELECTION FOR HEAT-SHOCK RESISTANCE IN LARVAL AND IN ADULT DROSOPHILA BUZZATII: 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 were artificially selected for higher survival to heat stress as adults, and two other lines were reared under a fluctuating thermal environment as larvae, 35°C for 6 h and 25°C for 18 h, to "naturally" 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°C for 6 h. Control lines were maintained separately for the adult and larval selection lines. A significant direct response to selection was found for the adult selection lines. However, larvae of these adult selection lines were no more heat resistant than were larvae of the control lines. One of the two larval selection lines increased significantly in heat resistance as larvae. However, adult heat resistance was similar for lines selected as larvae and the corresponding control lines maintained at 25°C. Changes in developmental time accompanied changes in survival after stress in both sets of lines selected for increased heat resistance.