Embryonic temperature tolerances of five species of Japanese brown frogs, Rana japonica, R. tsushimensis, R. dybowskii, R. okinavana and R. tagoi, were reported. High-temperature limits at which a half of morulae or blastulae died before stage 25 (completion of operculum) are 33 C in R. japonica, 31 C in R. tsushimensis, 29 C in R. dybowskii and R. okinavana, and 25 C in R. tagoi. Low-temperature limits are above 4 C in R. japonica and below 4 C in R. tagoi. High-temperatue limits seem to correlate not with air temperature or shape of egg mass but with higher limit in the temperature fluctuation of breeding waters and egg diameter.

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