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

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Abstract
Daphnia pulex respond to water-borne chemicals released by predatory phantom midge larvae (Chaoborus spp.) with adaptive life-history and morphological 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 induced the development of neckteeth, a faster growth rate, larger size at maturity, and higher fecundity in D.pulex. There was no evidence of any costs associated with neckteeth production except a small increase in age at maturity. Endosulfan was lethal to free-swimming D.pulex only at 300 μg l–1, but caused significant mortality to embryos at concentrations as low as 0.1 μg l–1. It inhibited the development of neckteeth at 100 μg l–1, and reduced the growth rate of the induced morph at concentrations ≥0.1 μg l–1. Endosulfan had a unimodal effect on the expression of neckteeth in maternally-exposed daphnids, with maximal inhibition at intermediate concentrations. Endosulfan increased the number of neckteeth only in the first instar of maternally-exposed neonates at 200 μg l–1. More generally, the results of this study suggest that anthropogenic pollution may inhibit phenotypic plasticity, indirectly limiting the temporal and spatial range of affected species.

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