Fluctuating temperatures affect growth and production rates of planktonic ciliates

We measured the effect of fluctuating experimental temperatures on volume, growth rate, and production of 3 isolates of Urotricha furcata and 1 isolate of U. farcta. Laboratory experiment;;were conducted under constant (20 degrees C) and daily fluctuating (12:12 h) temperatures (19:21, 17:23, 15:25 degrees C). Experiments simulated temperature fluctuations that ciliates experience in natural environments. Fluctuating temperatures affected all parameters measured, suggesting that rate measurements at constant temperatures are not necessarily appropriate for modelling of processes in naturally fluctuating environments. Although there were significant effects of fluctuating temperature on parameter estimates, no universal trend was observed. Furthermore, effects under fluctuating conditions could not be predicted from mean estimates of measurements made over the temperature ranges. Finally, differences among isolates of U. furcata, from lakes 100s of km apart, were as large as differences between U. furcata and U. farcta; this suggests that various ecotypes exist among morphologically identical isolates.