Formation and reversibility of inducible morphological and behavioral defenses in Daphnia magna

Inducible defense is an effective way for prey to improve its fitness under fluctuating predation risks. While the formation and reversibility of diverse inducible defensive traits are still not fully understood. This study focused on the inducible morphological and behavioral traits of Daphnia magna in the process of predator come and go, which were simulated by adding and removing fish kairomone, respectively. Results showed that D. magna exposed to fish kairomone inhabited deeper water and owned smaller individual size. The adult D. magna exposed to fish kairomone could develop the same inducible defensive traits as the individuals exposed to fish kairomone from neonate. In terms of the complete formation time, behavior (6 days) was faster than morphology (17 days). Besides, by removing kairomone after maturity, the inducible defensive traits of D. magna could reverse to the traits of the individuals never exposed to fish kairomone. In terms of the reversal time, behavior (18 days) was similar to morphology (21 days). Furthermore, the reversal degrees of morphological and behavioral defenses were equal at any specific time point. Such results suggest that inducible behavioral defensive traits are not always more reversible than inducible morphological defensive traits.