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ABSTRACT
Two-spined and unspined Brachionus calyciflorus were cultured at 15°C, 20°C, 25°C, and 30°C to investigate their differences in life expectancy at hatching, average lifespan, generation time, net reproductive rate, intrinsic rate of population increase, proportion of mictic offspring, and proportion of spined offspring. Life history parameters between the two B. calyciflorus morphotypes differed with temperature. At 15°C, the unspined rotifer had a higher intrinsic rate of population increase than the two-spined rotifer. At 20°C, the proportion of spined offspring produced by the two-spined rotifer was higher than that produced by the unspined rotifer. At both 25°C and 30°C, the two-spined rotifer had a longer average lifespan than the unspined rotifer. At 30°C, net reproductive rate of the two-spined rotifer was higher than that of the unspined rotifer. The responses in average lifespan, net reproductive rate, intrinsic rate of population increase, and proportion of spined offspring to increasing temperature differed between the two morphotypes. When the temperature increased from 20°C to 30°C, the rate of reduction of average lifespan of unspined rotifers was higher than that of two-spined rotifers. The net reproductive rate of the two-spined rotifer at 30°C was the highest, but the net reproductive rates of unspined rotifer at all the four temperatures were similar. When the temperature increased from 15°C to 20°C, the intrinsic rate of population increase of the unspined rotifer decreased faster than that of the two-spined rotifer. The proportion of spined offspring produced by the two-spined rotifer at all temperatures were similar, but the proportion of spined offspring produced by the unspined rotifer at 15°C was higher than that at 20°C, and both of them were similar with those at 25°C and 30°C. At all the four temperatures, each morphotype of B. calyciflorus produced two-spined and unspined offspring. At 25°C, two-spined rotifer also produced single-spined offspring.