The Fruit Morphometrics And Fruit Type Evolution Of Lithocarpus

Stone oaks,or Lithocarpus species of Fagaceae(about 320 species)are important canopy trees in the tropical and subtropical forests over East Asia,with great ecological importance as well as great economical value.The dominant fruit morphological variation of this genus is crucial to understand the species diversity and evolutionary history of Lithocarpus.In this study,we quantified multiple fruit morphological and physical properties of 2618 fruits representing 169 species widely distributed over China and Southeast Asia,and combined the phylogenetic relationship of 72 Lithocarpus species constructed from 9 genes.Our study shed lights on understanding the fruit morphological differentiation and fruit type evolution of Lithocarpus: the two major fruit types could represent fruit morphological polymorphism at the level of Lithocarpus,of which their morphological and physicochemical defense trade offs were identified: the smaller-seeded acorn fruit type(AC)is morphologically similar to Quercus acorn,and their thin pericarp represents weak physical defense,with high antifeedants in seeds as strong chemical defense;whereas the enclosed receptacle fruits type(ER)is larger in size,and extremely extended and thickened receptacle represents strong physical defense to the seed,the seed of which are high in nutrients.We also found that the enclosed receptacle fruit(ER)should be a derived type that had evolved independently several times in different evolutionary linages,which could be result of convergent evolutions.Since the differentiation of the two fruit types was not strongly correlated with evolution,we speculated that the differentiation between two fruit types could be driven by different predation pressures.In addition,ancestral state reconstruction supported the most important ancestral area of Lithocarpus is the tropics.In conclusion,this study not only clarified the fruit morphological and physical differentiation of the stone oaks,but also revealed the evolutionary relationship between the two fruit types of Lithocarpus.By providing the theoretical basis to understand the coexistence and diversity of Lithocarpus species,this study is also a template for fruit morphological evolution studies in the future.