Effects of endosulfan on Chaoborus-induced life-history shifts and morphological defenses in Daphnia pulex

Daphnia pulex respond to water-borne chemicals released by predatory phanto m midge larvae (Chaoborus spp.) with adaptive life-history and morphologica l responses. These responses can be modified by some classes of pesticides. The aim of this study was to measure the effects of a cyclodiene pesticide , endosulfan, on the Chaoborus-induced responses of D. pulex. Chaoborus ind uced the development of neckteeth, a faster growth rate, larger size at mat urity, and higher fecundity in D. pulex. There was no evidence of any costs associated with neckteeth production except a small increase in age at mat urity. Endosulfan was lethal to free-swimming D. pulex only at 300 mu g l(- 1), but caused significant mortality to embryos at concentrations as low as 0.1 mu g l(-1) . It inhibited the development of neckteeth at 100 mu g l(- 1), and reduced the growth rate of the induced morph at concentrations grea ter than or equal to 0.1 mu g l(-1). Endosulfan had a unimodal effect on th e expression of neckteeth in maternally-exposed daphnids, with maximal inhi bition at intermediate concentrations. Endosulfan increased the number of n eckteeth only in the first instar of maternally-exposed neonates at 200 mu g l(-1). More generally, the results of this study suggest that anthropogen ic pollution may inhibit phenotypic plasticity, indirectly limiting the tem poral and spatial range of affected species.