Adaptive changes in degree of eye reduction in eyeless mutants of Drosophila melanogaster after thermal shock during the critical periods of faceted eye development.

Brief heating of the oocytes and larvae of eyeless mutants during the critical periods of faceted-eye development caused an increase in the thermal sensitivity of the eye rudiments, which led to an increase in the number of one-eyed individuals among the flies that hatched. These changes eye development were transmitted through a number of successive generations without exposure to additional thermal shock, by maternal inheritance. It was established that repeated heating of oocytes and larvae of eyeless mutants whose ancestors had been subjected to similar heating during the same stages of development caused a decrease rather than the expected increase in thermal sensitivity, i.e., there was an adaptive increase in the thermostability of the eye rudiments. Thus, the effect of reheating was the opposite of that of the original heating.