Data from: Effects of climate on reproductive investment in a masting species: assessment of climatic predictors and underlying mechanisms

1. Mechanisms by which climatic factors drive reproductive investment and phenology in masting species are not completely understood. Climatic conditions may act as a proximate cue, stimulating the onset of reproduction and indirectly increasing fitness through benefits associated with synchronous reproduction among individuals. Alternatively, climatic conditions may directly influence individual level allocation to reproduction and reproductive success through effects occurring independently of synchronous reproduction. We previously showed that masting in a ponderosa pine (Pinus ponderosa) population was strongly influenced by spring mean temperature two years before seed cone maturation (Ti-2). However, recent work shows that the difference in temperature between previous growing seasons (ΔT) is more predictive of reproductive investment in long-lived tree species. 2. Here we compared four candidate models that predict seed cone production in P. ponderosa based upon different climatic factors (including Ti-2 and ΔT models). After determining the best climatic predictor, we tested for a potential mechanism by which climate might directly influence seed cone production independent of benefits via synchrony, namely effects of temperature on trade-offs between current and past reproduction (determined by underlying resource availability). 3. We found that Ti-2 (rather than ΔT) was the best predictor of seed cone production. We further show that this same climatic factor exerts a direct fitness benefit to individuals by reducing the strength of trade-offs between current and past reproductive efforts. 4. Synthesis: We demonstrate that a single climatic factor provides fitness benefits to individuals directly, by weakening reproductive trade-offs, and indirectly through the benefits associated with synchrony and masting. This suggests a mechanism for the origin and maintenance of masting: individuals initially respond to climatic cues that directly enhance reproduction (e.g. lower reproductive costs through weakened trade-offs) and this dynamic, expressed across multiple individuals, reinforces these benefits through the economies of scale associated with synchrony and masting.

1. 目前学界尚未完全阐明气候因子驱动结实同步现象（masting）物种生殖投入与物候的内在机制。气候条件可作为近因线索，刺激生殖启动，并通过个体间同步生殖带来的收益间接提升个体适合度；或者，气候条件也可通过独立于同步生殖的效应，直接影响个体的生殖资源分配与生殖成功率。本团队此前的研究表明，美国黄松（Pinus ponderosa）种群的结实同步现象显著受球果成熟前两年春季平均气温（Ti-2）调控。然而近期研究发现，前序生长季间的气温差值（ΔT）对多年生木本植物的生殖投入更具预测性。
2. 本研究对比了4种基于不同气候因子（包含Ti-2与ΔT模型）预测美国黄松球果产量的候选模型。在确定最优气候预测因子后，我们验证了一条潜在机制：气候可独立于同步生殖收益直接影响球果产量，即气温通过作用于当前与过往生殖事件间的权衡（由潜在资源可获得性决定）发挥调控作用。
3. 本研究发现，Ti-2（而非ΔT）是球果产量的最优预测因子。进一步研究表明，该气候因子可通过削弱当前与过往生殖投入间的权衡强度，直接为个体带来适合度收益。
4. 综合分析：本研究证实，单一气候因子可通过两条途径为个体带来适合度收益：一是通过削弱生殖权衡直接提升生殖表现，二是借助个体间同步生殖与结实同步现象带来的收益实现间接增益。该结果为结实同步现象的起源与维持机制提供了理论解释：植物个体最初会响应可直接提升生殖能力的气候线索（例如通过削弱权衡降低生殖成本），当这一动态在种群内多个个体间表达时，便会通过同步生殖与结实同步现象带来的规模效应进一步强化上述收益。