Stone oaks, or Lithocarpus species of Fagaceae are ecologically important canopy trees in the tropical and subtropical forests over East Asia, and the fruits of which are important food sources for insects and vertebrates there. The great fruit morphological variation of this genus represents two fruit types, acorn and enclosed receptacle fruit types. However, the evolutionary mechanisms of differentiation into these two fruit types with contrasting morphology remain a puzzle. To reveal the morphogenetic properties of two fruit types, we observed tissue differentiation and development among 20 Lithocarpus species from fruit set to maturity. Unlike in fruits of Quercus, the endocarp differentiation in Lithocarpus fruits occurred later than exocarp and mesocarp. Cupules provided further protection of developing seeds, particularly of acorn-type fruits. Fruits of Lithocarpus and Quercus acorns share similar insect predators. At fruit set, both acorn and enclosed receptacle types were largely identical, with similar tissue morphology and the sequence of differentiation. The distinct difference between two fruit types at maturity came from varied rates and degrees of development between the pericarp and receptacle tissues. We found that heterochrony between two tissues could create substantially divergent ecological strategies for protection and dispersal of their seeds, which is essential for the evolution of two fruit types.

中文翻译：

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栎果（Fagaceae）的果实发育及其异时性在其进化中的作用。

石橡树或菊科的石栎属物种是东亚热带和亚热带森林中具有重要生态意义的树冠树，其果实是那里昆虫和脊椎动物的重要食物来源。该属的果实形态变化很大，代表了两种果实类型，橡子和封闭的容器果实类型。然而，分化为这两种具有相反形态的水果的进化机制仍然是一个难题。为了揭示两种水果类型的形态发生特性，我们观察了从坐果到成熟的20种石栎物种的组织分化和发育。与栎类果实不同，石果果实中的内果皮分化发生在外果皮和中果皮之后。吸盘为种子的发育提供了进一步的保护，特别是橡子类水果。栎果和栎橡子的果实具有相似的昆虫食肉动物。在坐果期，橡子和封闭容器的类型基本相同，具有相似的组织形态和分化顺序。两种水果类型在成熟时的明显区别来自果皮和容器组织之间不同的速率和发育程度。我们发现，两种组织之间的异时性可以为保护和分散其种子创造出实质上不同的生态策略，这对于两种水果类型的进化至关重要。两种水果类型在成熟时的明显区别来自果皮和容器组织之间不同的速率和发育程度。我们发现，两种组织之间的异时性可以为保护和分散其种子创造出实质上不同的生态策略，这对于两种水果类型的进化至关重要。两种水果类型在成熟时的明显区别来自果皮和容器组织之间不同的速率和发育程度。我们发现，两种组织之间的异时性可以为保护和分散其种子创造出实质上不同的生态策略，这对于两种水果类型的进化至关重要。