Predator Induced Morphology Plasticity In The Rotifer Brachionus Calyciflorus

In many small planktonic rotifers, predator kairomones induce the developmentof longer spines, which can provide effective post-contact defense against thepredators. This study is used the common herbivorous zooplankton Brachionuscalyciflorus as the research subject, to investigate the kairomones of predatorsinduced rotifers phenotypic plasticity reactions. We use the B. calyciflorus-Asplanchnabrightwelli models to study the kairomones of predators induced rotifers defensivemorphology development.We use two clones of B. calyciflorus (BJ-clone and LY-clone) to carry out theexperiment, our study observed that the relationship between the density of predatorAsplanchna (the concentration of kairomones) and the length or relative length ofposterolateral spine of B. calyciflorus is a significant linear regression model. Thelength or relative length of the posterolateral spine increased with the increase in theconcentration of predator Asplanchna kairomones, resulting in a lineardosage-response pattern of predator Asplanchna kairomones induction of defensivemorphology in B. calyciflorus.Maternal effects on the predator induction of defensive morphology are regardedas an adaptive strategy. A mother can anticipate and transmit environmentalconditions related to predation risk to offspring of the same generation or succeedinggenerations, to improve the ability of offspring to defense the ingestion of predators.In both B. calyciflorus clones the rotifers posterolateral spine development wassignificantly affected by the exposure time to Asplanchna and birth order. The lengthor relative length of the posterolateral spine decreased to comparatively low levels inthe offspring with late birth order; however, spine development in these late-bornoffspring was also evident than those in the control groups. A step-wise weakenedmaternal effect as birth order progresses may possibly occur because of the dilution ordecomposition of unknown factors in a maternal body during successiveparthenogenetic offspring. Significant differences (comparison of K–with K+→K–,and K+with K–→K+) were detected between the length and the relative length of theposterolateral spine of both rotifer clones in the same F1generation but differentmaternal environments. Furthermore, these patterns were observed in the F2generation of the two Brachionus clones. These two experiments results indicated thatwithin-generation and transgeneration maternal effects exist in predators Asplanchna induced rotifer B. calyciflorus development of defensive morphology. Theinduction of Asplanchina kairomones inducible defense in rotifers may be responsiblefor such pathway, two possible hypotheses: First, kairomone may penetrate the bodycavity of mother and directly affect the primary oocyte or the oocyte undergoingoogenesis; Second, kairomone may directly function on the maternal body, therebyaffecting the physiological characteristics of mothers and trigger the release ofunknown factors (e.g., hormone), as a result, the growing oocyte is induced to developdefensive phenotypes. This experiment results support the second hypothesis.In our study, the B. calyciflorus fed N-depleted algae and P-depleted algae inhibitposterolateral spine development of defensive morphology. However it reduced thepopulation growth rate and net reproductive rate and reproduction period in rotifers.Algae food quality of B. calyciflorus survivorship rate and reproduction rate has noobvious impacts. Feeding on N-limitation or P-limitation of algae food than thenormal N and P level of algae food can reduce the population growth rate and netreproductive rate is result from reproduction period decrease. We observed that theP-limitation food alga is the most important factor to affect the expression ofdefensive morphology and the life history characteristic parameters. N-limitation andP-limitation of algae is the limitation of amino acid/protein synthesis in rotifers.