MORPHOLOGICAL RESPONSES OF 4 SPECIES OF CYCLOMORPHIC DAPHNIA TO A SHORT-TERM EXPOSURE TO THE INSECTICIDE CARBARYL

Four species of cyclomorphic Daphnia (D.pulex, D.galeata mendotae, D.retrocurva, D.lumholtzi) were exposed to the insecticide carbaryl for a short term (8-14 h) from the final embryonic stage to the first instar. Daphnia pulex formed neckteeth, and the remaining three Daphnia species developed high helmets and long tailspines. The results suggest that the development of such protuberant structures (anti-predator morphologies) in response to the insecticide exposure is a general phenomenon in Daphnia, and that stimuli on the nervous system of Daphnia may induce the morphological changes, which originally evolved as a response to predator kairomone. Two clones of D.pulex were examined and a clone which was more sensitive to the predator Chaoborus kairomone than another developed more marked neckteeth in response to carbaryl, suggesting that the sensitivity in morphological response to the insecticide may be related to the sensitivity to the kairomone.