Inducible chemical defences in primary producer - herbivore interactions: effects on population dynamics as a function of consumer trait diversity

化学防御是植物-食草动物相互作用中一类主要的诱导防御。尽管它们被广泛传播，但它们对捕食-被捕食系统中种群动态的影响尚未被调查。在这里，我们使用的浮游系统以蓝藻为主要生产者，以大型水蚤为食草动物。铜绿微囊藻产生已知的作为抗草食动物防御的蛋白酶抑制剂(PI)，当暴露于活跃的放牧草食动物时被诱导，这导致在放牧草食动物和初级生产者水平的防御程度之间产生反馈循环。初级生产者水平的这种塑料特性防御可以通过测量蓝藻的抑制物含量来量化。在这里，我们使用与大型水蚤的共培养来研究铜绿假单胞菌的诱导化学防御如何在初级生产者和消费者水平上影响种群动态，以及特征防御如何波动。为了进行比较，将使用非防御性蓝藻。我们进一步测试了种群动态和特征防御是如何在消费者水平上受到特征变异的影响的，方法是将一个系统与一个系统进行比较，该系统具有许多在对PI的特性耐受性方面不同的大D。我们将通过改变各种参数来进行受控增长实验，目的是在初级生产者层面上量化性状防御的权衡，并在消费者层面上量化性状耐受性的权衡。我们假设，这种由食草动物介导的化学反食草动物防御的诱导在消费者层面上反馈。更具体地说，我们预计蓝藻的这种诱导特征化学防御(I)强烈影响捕食者-猎物循环，并导致与单一捕食者-捕食者系统中无防御的蓝藻相比，捕食者和捕食者丰度的种群波动受到抑制。(Ii)在一个具有许多捕食者的系统中，捕食者-被捕食者的特性耐受性不同，强烈地影响捕食者-猎物的循环。我们预计，消费者层面特征多样性的增加将导致反应模式(波动/非波动)的灵活性增加，从而提高系统稳定性。

Chemical defences are a major class of inducible defences in plant-herbivore interactions. Despite being wide spread, they have not yet been investigated for their effects on population dynamics in predator-prey systems. Here we use a planktonic system with a cyanobacterium as primary producer and with Daphnia as herbivore. The cyanobacterium Microcystis aeruginosa produces known protease inhibitors (PIs) as anti-herbivore defence that are induced upon exposure to actively grazing herbivores, which results in a feedback loop between grazing herbivores and the degree of defence at the primary producer level. This plastic trait defence at the primary producer level can be quantified by measuring the inhibitor content of the cyanobacterium. Here we use a co-culture with Daphnia magna to investigate how the inducible chemical defence of M. aeruginosa affects population dynamics at the level of primary producer and consumer and how the trait defence fluctuates. For comparison a non-defended cyanobacterium will be used. We further test how population dynamics and the trait defence are affected by trait variability at the consumer level by comparing a system with one versus a system with many D. magna genotypes that differ with respect to the trait tolerance to the PIs. We will run controlled growth experiments by varying a variety of parameters with the aim to quantify the trade-off of the trait defence at the primary producer level and to quantify the trade-off of the trait tolerance at the consumer level.We hypothesize that this herbivore-mediated induction of a chemical anti-herbivore defence feeds back on the consumer level. More specifically we anticipate that this inducible trait chemical defence in the cyanobacterium(i) strongly affects predator-prey cycles and leads to dampened population fluctuations of prey and predator abundances in comparison to an undefended cyanobacterium in a single prey-predator system. (ii) strongly affects predator-prey cycles in a system with many predators that differ in the trait tolerance. We expect that increasing trait-diversity at the consumer level will result in increased flexibility of reaction patterns (fluctuating/non-fluctuating) and therefore in increased system stability.