Populations in nature are comprised of individual life histories, whose variation underpins ecological and evolutionary processes. Yet the forces of environmental selection that shape intrapopulation life-history variation are still not well-understood, and efforts have largely focused on random (stochastic) fluctuations of the environment. However, a ubiquitous mode of environmental fluctuation in nature is cyclical, whose periodicities can change independently of stochasticity. Here, we test theoretically based hypotheses for whether shortened (‘Fast’) or lengthened (‘Slow’) environmental cycles should generate higher intrapopulation variation of life history phenotypes. We show, through a combination of agent-based modelling and a multi-generational laboratory selection experiment using the tidepool copepod Tigriopus californicus, that slower environmental cycles maintain higher levels of intrapopulation variation. Surprisingly, the effect of environmental periodicity on variation was much stronger than that of stochasticity. Thus, our results show that periodicity is an important facet of fluctuating environments for life-history variation.

中文翻译：

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较慢的环境周期在人群中维持较大的生活史差异

自然界中的种群由个体生活史组成，其变异支撑着生态和进化过程。然而，塑造种群内生活史变异的环境选择力量仍然没有得到很好的理解，并且努力主要集中在环境的随机（随机）波动上。然而，自然界中普遍存在的环境波动模式是周期性的，其周期性可以独立于随机性而变化。在这里，我们测试了基于理论的假设，即缩短（“快速”）或延长（“慢”）环境周期是否应该产生更高的生活史表型的种群内变异。我们通过基于代理的建模和使用潮池桡足类的多代实验室选择实验相结合来展示Tigriopus californicus，较慢的环境周期维持较高水平的种群内变异。令人惊讶的是，环境周期性对变化的影响比随机性强得多。因此，我们的结果表明，周期性是生活史变化环境波动的一个重要方面。