Protistology The effect of cultivation temperature on differentiation for mating type in exconjugant clones of the ciliate Dileptus anser

The effect of cultivation temperature on differentiation of exconjugant clones for their mating types was studied in the ciliate Dileptus anser. Crosses of the clone # 7C (mating type I, MT I) with the clone # 155 (MT III) yielded 26 exconjugant F1 clones, one clone from each conjugant pair. Each young exconjugant clone was divided into two subclones. One of the subclones was further cultivated at 17 #С, the other one, at 25 #С. The clones were tested once a week with three test clones for their mating ability, and their sexual immaturity vs. maturity, what permitted to determine their MTs. Of 26 clones cultivated at 17 #С, two clones remained immature throughout the experiment (23 to 25 weeks after crossing), at 17 #С as well as at 25 #С. 24 subclones cultivated at 17 #С appeared to be mature by the 20th to 23rd week after crossing. Eight of them had MT I, six MT II, and ten MT III. Of 24 subclones cultivated at 25 #С, five changed their MTs early in their maturity state, and three others did so even twice. In other words, these subclones showed unstable differentiation for their MT (cf. Yudin and Uspenskaya, 2006). Later, 23 to 25 weeks after crossing, 17 subclones had MT I, 2 MT II, and 5 MT III. The distributions for MTs at 17 #С and 25 #С differed significantly (χ at 1= 0.05), MT I prevailing at 25 #С and MT III, at 17 #С.