LIFE-HISTORY VARIABILITY IN RESPONSE TO TEMPERATURE AND CHAOBORUS EXPOSURE IN 3 DAPHNIA-PULEX CLONES

In a 21-day life table experiment, we studied the role of temperature, exposure to Chaoborus obscuripes, and their interaction on life histo ry parameters and neck spine development in Daphnia pulex. We used thr ee D. pulex clones collected from different ponds in southwestern Finl and. In these ponds, temperature, predation pressure, and the clonal c omposition of Daphnia populations may vary substantially. Each clone w as exposed to Chaoborus-conditioned water or control water at 16 and 2 0 degrees C. Predator exposure and temperature affected significantly age and size at first reproduction and the total number of offspring i n Daphnia. Interaction between predator exposure and temperature appro ached significance for the age at first reproduction, and the interact ion between predator exposure and clone was significant for the same t rait. Temperature interacted with clonal origin for all reproductive p arameters studied. All three clones showed no or only weak morphologic al responses to Chaoborus. This indicates that the life history change s observed are independent of neck spine formation and may be adaptive in the presence of invertebrate predation.