Effect Of Predator On Sexual Reproduction In The Brachionus Rotifer Species

In present work we used Brachionus calyciflorus and B. angularis to test the cost of sex allocation. We used experimental ecology method in this study and discuss some questions from evolutionary ecology:1. Individual defense can reduce the possibility of prey to be killed by the predator. But as a result of between trade-off of energy allocation. Because sexual reproduction and individual defense requires larger energy investment. So we predict that an investment trade-off exists between inducible defence and sexual reproduction in B. calyciflorus. we predict that in the presence of the kairomones produced by Asplanchna brightwellii, B. calyciflorus will be induced defendive morphologies. Because the energy consumption, which B. calyciflorus will decrease its sex investment. The decrease of sex investment is defened as the decrease of the production of mictic offspring or resting eggs. Thus, we studied the sex investment of B. calyciflorus populations at three Asplanchna kairomone concentrations(0, 10, and 100 Asplanchna L-1) and two food levels(1 and 12 mg C L 1) to evaluate the sex cost of inducible defences. We also evaluated the crowding threshold required to trigger sex investment(i.e. lowest population density at which mictic female is produced) in B. calyciflorus under different kairomone and food treatments. Results showed that(i) the B. calyciflorus population exposed to kairomones produced offspring with elongated posterolateral spines;(ii) the production of mictic offspring and resting eggs decreased in the B. calyciflorus population exposed to kairomones, suggesting an investment trade-off exists between inducible defence and sex investment;(iii) the decrease in sex investment was higher at the high kairomone concentration than at the low kairomone concentration;(iv) the decrease of sex investment was higher at the low food level than at the high food level; and(v) the crowding threshold of the B. calyciflorus population increased upon exposure to kairomones.Brachionus angularis and B. calyciflorus belong to the genus Brachionus, under predation risk,it’s energy investment trends of sexual reproduction whether, consistent with B. calyciflorus or by other life history plasticity to avoid predation. Our result showed that the mictic rate of Brachionus angularis did not change obviously in the presense of kairomone.Therefore, under predation risk, the sex investment of B. angularis has no significant influence. But at the risk of predation, population of B. angularis obviously decreased number of offsprings. Experimental results show that B. angularis of Asplanchna kairomone reduced susceptibility to predators, but still able to resist the predation of Asplanchna. Therefore,We predicted that in the presence of predators, Brachionus angularis will develop individual defense.For example increase the thickness of carapace of Brachionus angulari. While the increase of the thickness of carapace reduced the number of offspring populations to some extent.