Data from: Parental environmental effects due to contrasting watering adapt competitive ability, but not drought tolerance, in offspring of a semi-arid annual Brassicaceae

1. Parental effects (PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats. 2. Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought. 3. Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the greenhouse. 4. Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours. 5. Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies. 6. Synthesis: This study demonstrates the important role of adaptive parental effects (PE) for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor.

1. 亲本效应（Parental effects, PE）在亲本与子代遭遇相似环境条件时，可具有适应性并提升子代适合度。然而，在因较强时间变异导致环境相似性难以出现的生境中，适应性亲本效应是否同样存在，目前仍不明确。具体而言，我们尚不清楚亲本效应能否使子代适应此类生境中邻体竞争水平的波动。
2. 本研究以半干旱一年生植物系统为研究对象，针对竞争与干旱这两类关键环境因子，检验了适应性亲本效应的存在性。研究区域的降雨具有随机性，而邻体竞争环境则具备部分可预测性：在降水充沛的丰年，由于种子产量较高，后续植物种群密度会随之升高。据此我们推测，亲本效应应使子代的竞争能力适应种群密度的这类（可预测的）波动，而非使子代的耐旱性适应干旱加剧发生的（不可预测的）情况。
3. 研究对象为一年生十字花科植物Biscutella didyma，将亲本植株分别置于适宜浇水条件与干旱条件下培养。随后在温室中，通过两种邻体处理与六种浇水水平的全因子组合实验，检测子代的适合度表现。
4. 来自适宜浇水条件下亲本的子代，其竞争能力更强。这一现象与物候期的微小偏移相关，但与亲本种子资源供给量的提升无关。来自干旱条件下亲本的子代，其耐旱性并未得到提升。此外，当子代在无邻体的环境中生长时，未检测到显著的亲本效应。
5. 我们的研究结果揭示了适应性亲本效应的一条新路径：当子代更可能遭遇高邻体密度时，其竞争能力会被诱导提升。结合耐旱性方面未发现适应性亲本效应这一结果，这强调了亲本与子代环境的相关性是适应性亲本效应演化的关键前提。本研究结果同时呼吁未来的亲本效应研究纳入邻体竞争效应的考量范畴。
6. 综合结论：本研究基于不同环境因子的可预测性，证实了在时间异质性环境中，适应性亲本效应（PE）对于植物适合度（针对邻体竞争）的重要作用，同时也揭示了其在耐旱性方面的局限性。