DeSoto L, Torices R, Rodríguez-Echeverría S, Nabais C
Centre for Functional Ecology, University of Coimbra, Coimbra, Portugal.
Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland.
Plant Biol (Stuttg). 2017 Jul;19(4):533-541. doi: 10.1111/plb.12566. Epub 2017 Apr 6.
The study of intraspecific seed packaging (i.e. seed size/number strategy) variation across different populations may allow better understanding of the ecological forces that drive seed evolution in plants. Juniperus thurifera (Cupressaceae) provides a good model to study this due to the existence of two subspecies differentiated by phenotypic traits, such as seed size and cone seediness (number of seeds inside a cone), across its range. The aim of this study was to analyse seed packaging (seed mass and cone seediness) variation at different scales (subspecies, populations and individuals) and the relationship between cone and seed traits in European and African J. thurifera populations. After opening more than 5300 cones and measuring 3600 seeds, we found that seed packaging traits followed different patterns of variation. Large-scale effects (region and population) significantly contributed to cone seediness variance, while most of the seed mass variance occurred within individuals. Seed packaging differed between the two sides of the Mediterranean Sea, with African cones bearing fewer but larger seeds than the European ones. However, no differences in seed mass were found between populations when taking into account cone seediness. Larger cones contained more pulp and seeds and displayed a larger variation in individual seed mass. We validated previous reports on the intraspecific differences in J. thurifera seed packaging, although both subspecies followed the same seed size/number trade-off. The higher seediness and variation in seed mass found in larger cones reveals that the positive relationship between seed and cone sizes may not be straightforward.We hypothesise that the large variation of seed size found within cones and individuals in J. thurifera, but also in other fleshy-fruited species, could represent a bet-hedging strategy for dispersal.
研究不同种群间种内种子包装（即种子大小/数量策略）的变化，可能有助于更好地理解驱动植物种子进化的生态力量。刺柏（柏科）是研究这一问题的良好模型，因为在其分布范围内存在两个因表型特征（如种子大小和球果含籽量，即一个球果内的种子数量）而分化的亚种。本研究的目的是分析欧洲和非洲刺柏种群在不同尺度（亚种、种群和个体）下的种子包装（种子质量和球果含籽量）变化，以及球果和种子性状之间的关系。在打开5300多个球果并测量3600颗种子后，我们发现种子包装性状遵循不同的变化模式。大规模效应（区域和种群）对球果含籽量的方差有显著贡献，而大部分种子质量方差发生在个体内部。地中海两岸的种子包装存在差异，非洲球果的种子数量较少但个头比欧洲的大。然而，在考虑球果含籽量时，种群间种子质量没有差异。较大的球果含有更多的果肉和种子，且个体种子质量的变化更大。我们验证了之前关于刺柏种子包装种内差异的报道，尽管两个亚种都遵循相同的种子大小/数量权衡。在较大球果中发现的更高含籽量和种子质量变化表明，种子与球果大小之间的正相关关系可能并非简单直接。我们推测，在刺柏以及其他肉质果实物种的球果和个体中发现的种子大小的巨大差异，可能代表了一种用于传播的风险分摊策略。
