Joint effects of predation risk and food nutrient on sexual and asexual reproductions, and morphological defenses of freshwater rotifer Brachionus calyciflorus

Abstract

Ecological stoichiometry predicts that the extent to which herbivores are limited by nutrients depends on their metabolic demands. Nonconsumptive effects (NCEs) caused by predators have been demonstrated to trigger not only inducible defenses but also physiological stresses in prey. Stressed prey always exhibit increased metabolism and decreased nutrient deposition (e.g., nitrogen and phosphorus) as physiological stress responses to their predators. Consequently, prey exposed to predation risk should reduce demands for nutrients intake and become adaptive to nutrient limitations. In this study, results obtained from classic Brachionus–Asplanchna model revealed that Brachionus calyciflorus fed with full nutrient algal food showed energetic costs, e.g., reduced investment in asexual (lifetime fecundity) and sexual (mixis ratio) reproductions, in response to predation risk. However, reduction in sexual and asexual reproductions diminished when herbivorous Brachionus were supplied with nitrogen- or phosphorus-limited algal food. Moreover, long posterolateral spines and high posterolateral spine-body length ratio developed in either nitrogen- or phosphorus-deficient conditions containing Asplanchna kairomones, indicating an additive effect of nutrient limitation and predation risk on posterolateral spine development in Brachionus. The findings of this study highlighted predator-facilitated adaptation of prey to nutrient limitations of primary producers, which may have implications in understanding roles of NCEs in regulating trophic interactions.