Physiological And Biochemical Responses Of The Rotifer Brachionus Calyciflorus In Predation Risk

The prey can defend themselves from predator by changing their morphology and behavior when predators exist. However, the effects of predator on physiological stress and biochemical composition in prey are rarely concerned and studied. The theory of Ecological stoichiometry predicts that prey will produce a series of physiological responses such as gluconegenesis, increased respiration, accelerate the elimination of the N, P in the body, resulting increasing the ratio of C: N and C: P, when the prey is exposed to the risk of predation. Furthermore, predators can force prey to start to escape behavior, thus increase the metabolic rate, result in oxidative stress, which induced the process of antioxidant defense in vivo. Therefore, in this study, we use Brachionus calyciflorus and Asplanachna brightwellii to verify the following three hypotheses: ①The ratio of C: N and C: P in Brachionus calyciflorus will be increased significantly under the risk of predation by Asplanchna brightwellii. ②The activity of antioxidant enzyme in Brachionus calyciflorus will be increased significantly, at the same time, the content of malondialdehyde(MDA) also will be increased markedly under the risk of predation by Asplanchna brightwellii. ③ The risk of predation by Asplanchna brightwellii can induce the changes of element mass ration in Brachionus calyciflorus, for example, the ration of C: N and C: P will increase. For this reason, Brachionus calyciflorus can adapt to the food with low nitrogen and low phosphorus very well. In addition, the defensive shape of Brachionus calyciflorus will be inhibited, to some extent, because of the consumption of energy. What’s more, the quality of food with low nitrogen and low phosphorus is too low to provide enough energy.Our results suggest that(1) when Brachionus calyciflorus exposed to the risk of predation by Asplanchna brightwellii, they will grow defensive shape(i.e. increase the Length of posterlateral spine). At the same time, the percentage of carbon(C %) of Brachionus calyciflorus under the risk of predation was significantly higher than Brachionus calyciflorus which non-exposed to the risk of predation. The percentage of nitrogen and phosphorus(N % and P %) was also significantly reduced, the ratio of C: N, C: P were significantly increased. This shows that Brachionus calyciflorus under the risk of predation are not only grow defensive shape but also the ration of C: N, C: P were significantly increased in their body.(2) B. calyciflorus with Asplanchna kairomone doesn’t avoid predators through escape behavior. Swimming speed of B. calyciflorus with Asplanchna kairomone was not significant differences compare to B. calyciflorus without Asplanchna kairomone. But it will lead to increase oxidative stress and induce the process of antioxidant defense. So the activity of antioxidant enzyme(CAT, POD and SOD) in B. calyciflorus will be increased significantly, at the same time, the content of MDA(represent degree of oxidative damage) also will be decreased markedly.(3) B. calyciflorus feeding different quality food(N and P-rich food,N-deficient food and P-deficient food), the results show that the B. calyciflorus feeding N-depleted algae and P-depleted algae will inhibit the rate of population growth and reproduction, P-deficient food plays a major role in limiting. On the other hand, when B. calyciflorus under the risk of predation, the ratio of C: N、C: P in vivo will be elevated. Thus B. calyciflorus feeding N-deficient food and P-deficient food will have better adaptability under the risk of predation. In addition, the rate of population growth and reproduction were not significant difference. What’s more, the lifespan was significantly extended. The risk of predation is the most important factor on morphology defense. N-deficient food and P-deficient food will promote the formation of the body defense no matter whether B. calyciflorus with Asplanchna kairomone. N-deficient food will extend length of posterlateral spine in B. calyciflorus significantly. The results suggested that prey will produce a series of responses(physiological and biochemical) to response risk of predation when the presence of predator.