Biological Sciences Department, California Polytechnic State University, San Luis Obispo, California, USA.
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, USA.
Ecology. 2022 Jul;103(7):e3698. doi: 10.1002/ecy.3698. Epub 2022 Apr 27.
Offspring size is a key functional trait that can affect subsequent life history stages; in many species, it exhibits both local adaptation and phenotypic plasticity. Variation among populations in offspring size may be explained by various factors, including local climatic conditions. However, geographic variation in climate may be partitioned into long-term and interannual sources of variation, which may differ in their effects on population mean offspring size. To assess environmental correlates of offspring size, we evaluated geographic variation in seed mass among 88 populations representing 6 species of Streptanthus (Brassicaceae) distributed across a broad climatic gradient in California. We examined the effects of temperature-mediated growing season length and precipitation on population mean seed mass to determine whether it is best explained by (1) long-term mean climatic conditions; (2) interannual climate anomalies (i.e., deviations in climate from long-term means) during the year of seed development, or (3) interactions between climate variables. Both long-term mean climate and climate anomalies in the year of collection were associated with population mean seed mass, but their effects differed in direction and magnitude. Relatively large seeds were produced at chronically wet sites but also during drier-than-average years. This contrast indicates that these associations may be generated by different mechanisms (i.e., adaptive evolution vs. phenotypic plasticity) and may be evidence of countergradient plasticity in seed mass. In addition, populations occurring in locations characterized by relatively long growing seasons produced comparatively large seeds, particularly among chronically dry sites. This study highlights the need to consider that the responses of seed mass to long-term versus recent climatic conditions may differ and that climate variables may interact to predict seed mass. Such considerations are especially important when using these patterns to forecast the long- and short-term responses of seed mass to climate change. The results presented here also contribute to our broader understanding of how climate drives long-term (e.g., local adaptation) and short-term (e.g., phenotypic plasticity) variation in functional traits, such as offspring size across landscapes.
后代大小是一个关键的功能特征，它可以影响后续的生活史阶段；在许多物种中，它表现出局部适应和表型可塑性。后代大小的种群间差异可以用各种因素来解释，包括当地的气候条件。然而，气候的地理变化可以分为长期和年际变化的来源，它们对种群平均后代大小的影响可能不同。为了评估后代大小的环境相关性，我们评估了加利福尼亚州分布广泛的气候梯度上的 6 种 Streptanthus（Brassicaceae）的 88 个种群的种子质量的地理变化。我们研究了温度介导的生长季节长度和降水对种群平均种子质量的影响，以确定它是最好地用（1）长期平均气候条件；（2）种子发育年份的年际气候异常（即气候与长期平均值的偏差）；还是（3）气候变量之间的相互作用来解释。长期平均气候和当年的气候异常都与种群平均种子质量有关，但它们的影响在方向和幅度上有所不同。在长期湿润的地方和相对干旱的年份都会产生相对较大的种子。这种对比表明，这些关联可能是由不同的机制（即适应性进化与表型可塑性）产生的，并且可能是种子质量反梯度可塑性的证据。此外，在生长季节相对较长的地方出现的种群产生的种子相对较大，尤其是在长期干旱的地方。本研究强调需要考虑到种子质量对长期和近期气候条件的反应可能不同，而且气候变量可能相互作用来预测种子质量。在使用这些模式预测种子质量对气候变化的长期和短期反应时，这种考虑尤为重要。这里呈现的结果也有助于我们更全面地了解气候如何驱动功能特征（如后代大小）在景观中的长期（例如，局部适应）和短期（例如，表型可塑性）变化。
