van Velzen Ellen, Etienne Rampal S
Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlands.
J Theor Biol. 2015 May 7;372:89-99. doi: 10.1016/j.jtbi.2015.02.027. Epub 2015 Mar 6.
Plant defense against herbivory comes at a cost, which can be either direct (reducing resources available for growth and reproduction) or indirect (through reducing ecological performance, for example intraspecific competitiveness). While direct costs have been well studied in theoretical models, ecological costs have received almost no attention. In this study we compare models with a direct trade-off (reduced growth rate) to models with an ecological trade-off (reduced competitive ability), using a combination of adaptive dynamics and simulations. In addition, we study the dependence of the level of defense that can evolve on the type of defense (directly by reducing consumption, or indirectly by inducing herbivore mortality (toxicity)), and on the type of herbivore against which the plant is defending itself (generalists or specialists). We find three major results: First, for both direct and ecological costs, defense only evolves if the benefit to the plant is direct (through reducing consumption). Second, the type of cost has a major effect on the evolutionary dynamics: direct costs always lead to a single optimal strategy against herbivores, but ecological costs can lead to branching and the coexistence of non-defending and defending plants; however, coexistence is only possible when defending against generalist herbivores. Finally, we find that fast-growing plants invest less than slow-growing plants when defending against generalist herbivores, as predicted by the Resource Availability Hypothesis, but invest more than slow-growing plants when defending against specialists. Our results clearly show that assumptions about ecological interactions are crucial for understanding the evolution of defense against herbivores.
植物抵御食草动物是有代价的,这种代价可能是直接的(减少用于生长和繁殖的资源)或间接的(通过降低生态表现,例如种内竞争力)。虽然直接成本在理论模型中已得到充分研究,但生态成本几乎未受到关注。在本研究中,我们结合适应性动态和模拟,将具有直接权衡(生长速率降低)的模型与具有生态权衡(竞争能力降低)的模型进行比较。此外,我们研究了能够进化的防御水平对防御类型(直接通过减少消耗,或间接通过诱导食草动物死亡(毒性))以及植物所防御的食草动物类型(广食性或专食性)的依赖性。我们发现三个主要结果:第一,对于直接成本和生态成本而言,只有当对植物的益处是直接的(通过减少消耗)时,防御才会进化。第二,成本类型对进化动态有重大影响:直接成本总是导致针对食草动物的单一最优策略,但生态成本可能导致分支以及不防御和防御植物的共存;然而,共存仅在防御广食性食草动物时才有可能。最后,正如资源可用性假说所预测的,我们发现快速生长的植物在防御广食性食草动物时的投入少于缓慢生长的植物,但在防御专食性食草动物时的投入多于缓慢生长的植物。我们的结果清楚地表明,关于生态相互作用的假设对于理解植物防御食草动物的进化至关重要。