Induction and reversibility of <i>Ceriodaphnia cornuta</i> horns under varied intensity of predation risk and their defensive effectiveness against <i>Chaoborus</i> larvae
Lei Gu, Xiaoqing Xu, Yannan Li, Yunfei Sun, Lu Zhang, Kai Lyu, Yuan Huang, Zhou Yang
Abstract
Abstract Phenotypic plasticity is common, and the induction and reversibility of plastic traits is closely related to the fitness of organisms in fluctuating environments. However, understanding the expression and reversion patterns of inducible traits in environments with fluctuating predation intensity is still a challenge. The present study focused on the inducible horns of Ceriodaphnia cornuta and its interaction with predation by Chaoborus larvae. We described the expression and reversion patterns of horns under increasing predation risks, which included response time, rate, and intensity. Additionally, we used predation trials to measure the effect of inducible horns on the survival rate and resistance to Chaoborus larvae predation by juvenile and adult C. cornuta . The results revealed that the size and expression patterns of horns at different body parts contributed to individual horn induction, which ultimately led to adaptive expression and reversion patterns under increasing predation risks. Specifically, the expression time and intensity increased linearly under increasing predation risks. Correspondingly, the reversion time also increased linearly, reversibility decreased linearly, and induction and reversion rates increased logarithmically. Corresponding with the plasticity pattern, predation trials showed that adult individuals with horns were remarkably less vulnerable to predation by Chaoborus larvae than undefended individuals. This finding provides a direct evidence of the benefit of inducible horns in C. cornuta . By combining benefits and response patterns, the present study provided a basic understanding of the ontogenetic plasticity of horns in C. cornuta . Furthermore, our study indicates that C. cornuta could be an efficient organism for understanding the induction and reversibility of inducible defensive traits and related interspecific relationships under fluctuating conditions in aquatic environments.