Life-history responses of Daphnia pulicaria to diets containing freshwater diatoms: Effects of nutritional quality versus polyunsaturated aldehydes

Abstract

Like marine diatoms, some freshwater diatoms produce α,β, γ,δ-polyunsaturated aldehydes (PUA) when damaged. Some of these oxylipins are suspected of impairing egg viability in marine copepods. To determine whether these compounds also play a role in influencing the trophic interactions in freshwater environments, we measured growth and reproduction of the cladoceran Daphnia pulicaria in response to diets composed of seven diatoms differing in PUA production. The juvenile growth rate of Daphnia varied with the diatom species, but was not related to oxylipin production. Egg hatching success was nearly 100% in all clutches for all diets, except with a diet of the decadienal producing Fragilaria sp., where it decreased dramatically in clutches 5-7. In vitro tests of egg hatching in the presence of PUA showed a dose-dependent inhibition for decadienal. Population parameters (i.e., life-time fecundity and instantaneous rate of population growth) were not affected by PUA, as the contribution of late clutches to them was negligible. Consequently, the wound-activated production of PUA by diatoms cannot be regarded as a defensive mechanism against Daphnia population recruitment. © 2005, by the American Society of Limnology and Oceanography, Inc.