Premise Timing of germination can strongly influence plant fitness by affecting seedling survival and by having cascading effects on later life‐history traits. In seasonal environments, the period favorable for seedling establishment and growth is limited, and timing of germination is likely to be under stabilizing selection because of conflicting selection through survival and fecundity. Moreover, optimal germination time may vary among genotypes because of inherent differences in later life‐history traits. Methods To examine how germination time affects survival, fecundity, and the relative fitness of two genotypes differing in time to first flower, we conducted a field experiment in an Italian population of the winter annual Arabidopsis thaliana, in which seedling establishment occurs mainly in November. We transplanted seedlings of the local genotype and of a Swedish genotype monthly from August to December and monitored survival and fecundity. Results Only seedlings transplanted in November and December survived until reproduction, and fitness of the November cohort was 35 times higher than that of the December cohort, indicating strong stabilizing selection on timing of germination. There was no evidence of conflicting selection: seedling survival, adult survival, and fecundity were all highest in the November cohort. Moreover, the relative fitness of the two genotypes did not differ significantly between cohorts. Conclusions The very narrow window of opportunity for seedling establishment was related to rapid seasonal changes in soil moisture and temperature, suggesting that rate of seasonal change is an important aspect to consider for understanding spatiotemporal variation in selection on phenological traits.

中文翻译：

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拟南芥地中海种群萌发时间的强稳定选择

前提 发芽时间可以通过影响幼苗存活和对后期生活史性状产生连锁效应来强烈影响植物健康。在季节性环境中，有利于幼苗建立和生长的时期有限，由于生存和繁殖的选择冲突，发芽时间很可能处于稳定选择之下。此外，由于晚年生活史特征的固有差异，最佳发芽时间可能因基因型而异。方法 为了检查发芽时间如何影响存活时间、繁殖力和两种不同基因型的相对适合度，我们在冬季一年生拟南芥的意大利种群中进行了田间试验，其中幼苗的建立主要发生在 11 月。我们从 8 月到 12 月每月移植当地基因型和瑞典基因型的幼苗，并监测存活率和繁殖力。结果仅11月和12月移栽的幼苗存活至繁殖，11月队列的适应度比12月队列高35倍，表明对发芽时间有较强的稳定选择。没有证据表明选择存在冲突：幼苗存活率、成虫存活率和繁殖力在 11 月的队列中都是最高的。此外，这两种基因型的相对适合度在队列之间没有显着差异。结论 幼苗建立的机会窗口非常狭窄与土壤水分和温度的快速季节性变化有关，