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-草食相互作用中一类主要的诱导防御。尽管它们分布广泛，但尚未研究它们对捕食者-猎物系统中种群动态的影响。在这里，我们使用一个浮游系统，蓝藻作为主要生产者，水蚤作为食草动物。铜绿微囊藻蓝藻产生已知的蛋白酶抑制剂（pi）作为抗草食动物防御，在暴露于主动放牧的草食动物时被诱导，这导致在初级生产者水平上放牧草食动物和防御程度之间的反馈循环。这种塑料性状防御在初级生产者水平可以通过测量蓝藻的抑制剂含量来量化。本研究采用与大水蚤共培养的方法，研究了铜绿假单胞菌诱导化学防御在初级生产者和消费者水平上如何影响种群动态，以及性状防御如何波动。为了比较，将使用非防御蓝藻。我们进一步测试了种群动态和性状防御是如何受到消费者水平性状变异的影响的，方法是比较一个系统与一个具有许多大鼠基因型的系统，这些基因型在性状对pi的耐受性方面存在差异。我们将通过改变各种参数来进行受控生长实验，目的是量化初级生产者一级性状防御的权衡，并量化消费者一级性状耐受性的权衡。我们假设这种草食动物介导的化学抗草食动物防御的诱导会反馈到消费者层面。更具体地说，我们预计蓝藻中的这种诱导特性化学防御(i)强烈影响捕食者-猎物周期，并导致与单一捕食者-捕食者系统中无防御的蓝藻相比，被捕食者和捕食者丰度的种群波动受到抑制。（ii）在具有许多不同性状耐受性的捕食者的系统中强烈影响捕食者-猎物循环。我们期望在消费者层面上增加特性多样性将导致反应模式（波动/非波动）的灵活性增加，从而提高系统的稳定性。

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.