De Lisle Stephen P, Rowe Locke
Department of Environmental and Life Sciences, Karlstad University, Karlstad, Sweden.
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Canada.
Evol Lett. 2023 Mar 20;7(2):67-78. doi: 10.1093/evlett/qrad009. eCollection 2023 Apr 1.
Phenotypic plasticity plays a key role in adaptation to changing environments. However, plasticity is neither perfect nor ubiquitous, implying that fitness costs may limit the evolution of phenotypic plasticity in nature. The measurement of such costs of plasticity has proved elusive; decades of experiments show that fitness costs of plasticity are often weak or nonexistent. Here, we show that this paradox could potentially be explained by condition dependence. We develop two models differing in their assumptions about how condition dependence arises; both models show that variation in condition can readily mask costs of plasticity even when such costs are substantial. This can be shown simply in a model where plasticity itself evolves condition dependence, which would be expected if costly. Yet similar effects emerge from an alternative model where trait expression itself is condition-dependent. In this more complex model, the average condition in each environment and genetic covariance in condition across environments both determine when costs of plasticity can be revealed. Analogous to the paradox of missing trade-offs between life history traits, our models show that variation in condition can mask costs of plasticity even when costs exist, and suggest this conclusion may be robust to the details of how condition affects trait expression. Our models suggest that condition dependence can also account for the often-observed pattern of elevated plasticity costs inferred in stressful environments, the maintenance of genetic variance in plasticity, and provides insight into experimental and biological scenarios ideal for revealing a cost of phenotypic plasticity.
表型可塑性在适应不断变化的环境中起着关键作用。然而，可塑性既非完美无缺，也非普遍存在，这意味着适应度成本可能会限制自然界中表型可塑性的进化。事实证明，衡量这种可塑性成本并非易事；数十年的实验表明，可塑性的适应度成本往往很微弱或根本不存在。在此，我们表明这一矛盾现象可能由条件依赖性来解释。我们开发了两个模型，它们在关于条件依赖性如何产生的假设上有所不同；两个模型均表明，即使可塑性成本很高，条件的变化也能轻易掩盖可塑性成本。这一点在一个可塑性本身进化出条件依赖性的模型中就能简单地体现出来，如果可塑性有成本，那么这是可以预期的。然而，在一个性状表达本身依赖于条件的替代模型中也会出现类似的效果。在这个更复杂的模型中，每个环境中的平均条件以及不同环境间条件的遗传协方差都决定了何时能够揭示可塑性成本。类似于生活史性状之间缺失权衡的矛盾现象，我们的模型表明，即使存在成本，条件的变化也能掩盖可塑性成本，并表明这一结论对于条件如何影响性状表达的细节可能具有稳健性。我们的模型表明，条件依赖性还可以解释在应激环境中经常观察到的可塑性成本升高的模式、可塑性遗传方差的维持，并为揭示表型可塑性成本的理想实验和生物学场景提供了见解。
