Evaluating the fitness consequences of plasticity in tolerance to pesticides

In a rapidly changing world, phenotypic plasticity may be a critical mechanism allowing populations to rapidly acclimate when faced with novel anthropogenic stressors. Theory predicts that if exposure to anthropogenic stress is heterogeneous, plasticity should be maintained as it allows organisms to avoid unnecessary expression of costly traits (i.e. phenotypic costs) when stressors are absent. Conversely, if exposure to stressors becomes constant, costs or limits of plasticity may lead to evolutionary trait canalization (i.e. genetic assimilation). While these concepts are well-established in theory, few studies have examined whether these factors explain patterns of plasticity in natural populations facing anthropogenic stress. Using wild populations of wood frogs that vary in plasticity in tolerance to pesticides, the goal of this study was to evaluate the environmental conditions under which plasticity is expected to be advantageous or detrimental. We found that when pesticides were absent, more plastic populations exhibited lower pesticide tolerance and were more fit than less plastic populations, likely avoiding the cost of expressing high tolerance when it was not necessary. Contrary to our predictions, when pesticides were present, more plastic populations were as fit as less plastic populations, showing no signs of costs or limits of plasticity. Amidst unprecedented global change, understanding the factors shaping the evolution of plasticity will become increasingly important.

在瞬息万变的当今世界，表型可塑性（phenotypic plasticity）或许是种群应对新型人为胁迫因子时实现快速适应的关键机制。理论预测，若人为胁迫的暴露环境存在异质性，则应维持表型可塑性——这一特性可让生物在胁迫因子缺失时，避免表达高成本的性状（即表型成本）。反之，若胁迫因子的暴露环境趋于恒定，表型可塑性的成本或局限可能会引发进化性状渠化（evolutionary trait canalization，即遗传同化）。尽管这些理论概念已得到充分确立，但鲜有研究验证这些因素能否解释自然种群在面临人为胁迫时的表型可塑性模式。本研究以对农药耐受性存在可塑性差异的野生林蛙种群为研究对象，旨在探究表型可塑性具有优势或劣势的环境条件。研究结果显示，在无农药存在的环境中，可塑性更强的种群其农药耐受性更低，但适合度却高于可塑性较弱的种群，这很可能是因为它们避免了在无需高耐受性时表达该性状所带来的成本。与我们的预测相反，当存在农药时，可塑性更强的种群其适合度与可塑性较弱的种群并无显著差异，未表现出表型可塑性的成本或局限相关迹象。在前所未有的全球变化背景下，解析驱动表型可塑性演化的相关因素将变得愈发重要。