Waterborne metals impair inducible defences in Daphnia pulex: morphology, life-history traits and encounters with predators


1.†Inducible defences may be temporary and favoured where predation is intermittent and have been demonstrated in several invertebrates and vertebrates when prey detect chemical cues (kairomones) released by predators. Daphnia pulex (a water flea) exposed to Chaoborus (midge larvae) kairomones produce small neckteeth on the dorsal surface of the head as a defence against this gape-limited predator and survive better in the presence of Chaoborus. Recent studies have shown that waterborne copper (Cu) impairs the induction of neckteeth which could lead to lower survival. 2.†Here, we examined the effects of Cu on morphological changes and shifts in life-history traits in D. pulex exposed to kairomone from Chaoborus americanus. We exposed D. pulex mothers to chemical cues of C. americanus fed on either D. pulex neonates or on brine shrimp Artemia salina, the same Chaoborus cues combined with an environmentally relevant concentration of copper (10†03BCg†L22121), or dechlorinated tap water. We examined several morphological characteristics of neonates and life-historical characteristics of adults as well as assessing survival of neonates by staging encounters with predators. 3.†Neonates from mothers exposed to kairomone plus copper had fewer and shorter neckteeth than neonates from mothers exposed to kairomone alone. Moreover, neonates exposed to Cu had lower survival during encounters with predators than neonates exposed to kairomone without Cu. 4.†Adult female Daphnia exposed to kairomones released more neonates within the first 24†h of brood release and emptied their brood pouches quicker than mothers not exposed to kairomones, irrespective of the presence of Cu. 5.†Impairment by metals of morphological defences in zooplankton could lead to a decline in population density and alter community structure.