The evolution of age-dependent plasticity

When organisms encounter environments that are heterogeneous in time, phenotypic plasticity is often favored by selection. The degree of such plasticity can vary during an organism’s lifetime, but the factors promoting differential plastic responses at different ages or life stages remain poorly understood. Here we develop and analyze an evolutionary model to investigate how environmental information is optimally collected and translated into phenotypic adjustments at different ages. We demonstrate that plasticity must often be expected to vary with age in a nonmonotonic fashion. Early in life, it is generally optimal to delay phenotypic adjustments until sufficient information has been collected about the state of the environment to warrant a costly phenotypic adjustment. Toward the end of life, phenotypic adjustments are disfavored as well because their beneficial effects can no longer be fully reaped before death. Our analysis clarifies how patterns of age-dependent plasticity are shaped by the interplay of environmental uncertainty, the accuracy of perceived information, and the costs of phenotypic adjustments with life-history determinants such as the relative strengths of fecundity and viability selection experienced by the organism over its lifetime. We conclude by comparing our results with expectations for alternative mechanisms, including developmental constraints, that promote age-dependent plasticity.

当生物体遭遇时间异质性环境时，表型可塑性（phenotypic plasticity）往往会被自然选择所青睐。这类可塑性的程度在生物体的整个生命周期中可能发生变化，但推动不同年龄或生命阶段产生差异化塑性响应的因素，目前仍未得到充分阐释。本文构建并分析了一个进化模型，以探究环境信息如何被最优地收集，并转化为不同年龄阶段的表型调整。我们的研究表明，表型可塑性通常会以非单调的模式随年龄变化：生命早期的最优策略往往是延迟表型调整，直至收集到足够的环境状态信息，以支撑需要付出成本的表型调整；而在生命后期，表型调整同样不受青睐，因为其有益效应在死亡前已无法完全获得。本研究阐明了年龄依赖性表型可塑性的模式，如何受环境不确定性、感知信息的准确性、表型调整成本，以及诸如生物体在一生中经历的繁殖力选择与存活力选择相对强度等生活史决定因素之间的相互作用所塑造。最后，我们将研究结果与其他可促进年龄依赖性表型可塑性的机制（包括发育限制（developmental constraints））的预期结果进行对比，以此作结。