Seed size shapes plant evolution and ecosystems, and may be driven by plant size and architecture, dispersers, habitat and insularity. How these factors influence the evolution of giant seeds is unclear, as are the rate of evolution and the biogeographical consequences of giant seeds. We generated DNA and seed size data for the palm tribe Borasseae (Arecaceae) and its relatives, which show a wide diversity in seed size and include the double coconut (Lodoicea maldivica), the largest seed in the world. We inferred their phylogeny, dispersal history and rates of change in seed size, and evaluated the possible influence of plant size, inflorescence branching, habitat and insularity on these changes. Large seeds were involved in 10 oceanic dispersals. Following theoretical predictions, we found that: taller plants with fewer-branched inflorescences produced larger seeds; seed size tended to evolve faster on islands (except Madagascar); and seeds of shade-loving Borasseae tended to be larger. Plant size and inflorescence branching may constrain seed size in Borasseae and their relatives. The possible roles of insularity, habitat and dispersers are difficult to disentangle. Evolutionary contingencies better explain the gigantism of the double coconut than unusually high rates of seed size increase.

译文

:种子大小决定着植物的进化和生态系统,并且可能受植物大小和建筑,分散器,生境和孤立性的驱动。这些因素如何影响大种子的进化,以及大种子的进化速度和生物地理后果,尚不清楚。我们生成了棕榈部落无花果科(Arecaceae)及其亲缘的DNA和种子大小数据,这些数据显示了种子大小的广泛差异,其中包括世界上最大的双椰子(Lodoicea maldivica)。我们推断出它们的系统发育史,传播史和种子大小的变化率,并评估了植物大小,花序分支,生境和孤立对这些变化的可能影响。大种子参与了10次海洋传播。根据理论预测,我们发现:花序少的高大植物产生了更大的种子;岛屿上的种子大小趋向于更快地进化(马达加斯加除外);喜欢深色阴影的紫苏科的种子往往更大。植物大小和花序分支可能会限制紫菜科及其近缘种的种子大小。岛屿,栖息地和分散体的可能作用很难解开。进化上的偶然性比双子椰子种子尺寸的异常高的增长率更好地解释了双椰子的巨大优势。

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