Casper Brenda B, Heard Stephen B, Apanius Victor
Department of Biology, University of Pennsylvania, 19104-6018, Philadelphia, PA, USA.
Oecologia. 1992 May;90(2):212-217. doi: 10.1007/BF00317178.
A reduction in seed number per fruit is recognized as a common evolutionary trend among flowering plants. In order to evaluate the ecological role of single-seededness and its possible adaptive significance, we used van Roosmalen's (1985) descriptions of fruits for woody species in the Guianan flora to identify fruit and seed characters and dispersal syndromes associated with the single-seeded trait. We coded the following characters: seed number (one seed or more than one seed), fleshiness (dry or fleshy), dehiscence (dehiscent or indehiscent), dispersal syndrome, seed size (length), and fruit size (length). We ordered the data in a multi-dimensional contingency table and used maximum likelihood logistic regression to identify traits significantly correlated with single-seededness. Seed size and fruit size were treated as quantitative variables. Indehiscence and endozoochory are positively associated with single-seededness, with indehiscence contributing most to the best-fit model. Fruit size and seed size are also important with the probability of single-seededness generally increasing with seed size and decreasing with fruit size, although a (fruit size) x (seed size) interaction term is significant. Dry fruits are positively associated with single-seededness and dispersal by synzoochory or myrmecochory negatively associated when the full data set is examined, but neither parameter is significant in two models constructed to remove effects of phylogeny. A nested ANOVA revealed that most variation occurs below the family level for almost all of the traits considered, with the exception of the dry vs. fleshy trait for which there is no variation within genera. We argue that the strong association between indehiscence and single-seededness suggests selective advantages for single-seeded dispersal units but acknowledge that energetic trade-offs between seed number and seed size probably also occur. We suggest that the post-dispersal fates of seeds - especially those deposited in clumps by endozoochory - should be examined with the idea of identifying selective pressures on seed number per fruit.
果实种子数量减少被认为是开花植物中一种常见的进化趋势。为了评估单粒种子的生态作用及其可能的适应意义，我们利用范·罗斯马伦（1985年）对圭亚那植物区系木本物种果实的描述，来确定与单粒种子性状相关的果实和种子特征以及传播综合征。我们对以下特征进行编码：种子数量（一粒种子或多于一粒种子）、肉质性（干燥或肉质）、开裂性（开裂或不开裂）、传播综合征、种子大小（长度）和果实大小（长度）。我们将数据整理到一个多维列联表中，并使用最大似然逻辑回归来确定与单粒种子显著相关的性状。种子大小和果实大小被视为定量变量。不开裂和内果皮传播与单粒种子呈正相关，其中不开裂对最佳拟合模型的贡献最大。果实大小和种子大小也很重要，单粒种子的概率通常随种子大小增加而增加，随果实大小减小而减小，尽管（果实大小）×（种子大小）交互项显著。当检查完整数据集时，干果与单粒种子呈正相关，而通过共传播或蚁播传播呈负相关，但在构建的两个去除系统发育影响的模型中，这两个参数都不显著。嵌套方差分析表明，几乎所有考虑的性状，除了干燥与肉质性状在属内没有变异外，大部分变异发生在科级以下水平。我们认为，不开裂与单粒种子之间的强关联表明单粒种子传播单位具有选择优势，但也承认种子数量和种子大小之间可能也存在能量权衡。我们建议，应研究种子传播后的命运——尤其是那些通过内果皮传播成簇沉积的种子——以确定对每个果实种子数量的选择压力。
