[Thermal selection of zygotes and heat resistance of the body and muscle tissue in tadpoles].

A study was made of the group (family) thermal selection of zygotes for heat resistance of the organism and muscles of the grass frog Rana temporaria L. at the initial and final stages of development. The average duration of thermal effect (37 degrees C), followed by a 50% lethality of affected zygotes (LD50), served a criterion of heat resistance of zygotes in each particular single clutch. The average time of survival at 34 degrees C served as criterion of heat resistance in tadpoles. The time of the loss of muscle contraction in response to electrical stimulus at 37 degrees C served as index of heat resistance of muscle tissue. The data presented show that the thermal elimination of 90% of zygotes failed to result in any directed shift in thermoresistances of the organism and muscles in animals grown from the most heat resistant clutches.