Inducible defenses: The relevance of chemical alarm cues in Daphnia

Abstract

Many aquatic organisms use chemical cues to recognize predators and to activate inducible defenses. In zooplankton, most of these cues are thought to be kairomones released by specific predators. However, in several other organisms, e.g., fish and amphibians, alarm signals from conspecifics also provide reliable cues. We tested whether alarm substances also act as chemical cues in Daphnia and assessed their relevance compared with predator kairomones. Water-borne cues from macerated conspecifics altered morphology in all Daphnia species tested (Daphnia cucullata, Daphnia longicephala, and Daphnia lumholtzi). However, kairomones released by feeding predators had distinctly stronger effects. In D. cucullata, we tested for the relevance of predator diet and found that the increase in relative helmet length was most pronounced when the predator was fed with conspecifics instead of heterospecifics. Cross-species experiments with alarm substances also revealed that D. cucullata is more sensitive to info-chemicals from macerated conspecifics than to chemical cues from D. magna. Unspecific alarm cues together with cues released by predators consuming prey may form a blend of chemicals that indicates predation risk and activates inducible defenses in nature.

Scaling-up anti-predator phenotypic responses of prey: impacts over multiple generations in a complex aquatic community

“…the cyclopoid/calanoid ratio, are likely to be strongly context-dependent. One important factor that could affect the relative magnitude of NCEs on different species is the recent diet of fishes, as fish diet has been shown to affect the magnitude of phenotypic responses of zooplankton [45].…”

Alarm substance from adult zebrafish alters early embryonic development in offspring

“…Chivers & Smith 1998;Ferrari et al 2007;Shabani et al 2008) and induced defences (Schoeppner & Relyea 2005;Laforsch & Beccara 2006;Hagman et al 2009). Most studies on effects of alarm cues are restricted to juveniles or adults, with effects on early embryonic development virtually unknown.…”

Predator-induced phenotypic plasticity within- and across-generations: a challenge for theory?

“…Each morning, more than 200 D. ambigua were added as prey to the aquaria. Injured Daphnia emit chemical cues that contribute to the magnitude of the phenotypic response to predation [37]. Our conditioned media probably contained both fish kairomones and Daphnia 'alarm cues'.…”