Thermal avoidance and preference in Daphnia magna

1. Water fleas (Daphnia magna) bred at 23 degreesC were non-responsive to t emperatures between 13 and 25 degreesC. 2. At the lower (11 degreesC) and upper limits (30 degreesC) their klinokin etic avoidance behaviour showed a larger intraindividual than interindividu al variation. 3. Thermal sensitivity for avoidance responses in D. magna was about 1.5 de greesC. 4. For D. magna bred for one parthenogenetic generation at 14 degreesC heat avoidance temperature was about 8 degreesC lower, and cold avoidance tempe rature was about 1 degreesC higher than in D. magna from 23 degreesC. 5. In group experiments the animals showed some preference for the acclimat ion temperature. 6. Cold induced stenothermy and warm induced eurythermy in D. magna were re lated to the mode of reproduction. (C) 2000 Elsevier Science Ltd. All right s reserved.