Determinants of fleshiness or dryness for fruits at maturity: fruit shapes and pericarp permeability

[A hypothesis was proposed that fleshiness or dryness of fruits at maturity were determined just by fruit shapes and pericarp permeability influenced by heterogeneous habitats] The ecological origins of diverse fruit types still remain unresolved due to the lack of knowledge about fruit water content variation patterns during fruit development and after fruit maturity. In this study, we explore factors influencing fleshiness or dryness of fruits at maturity through examining the water content variation patterns before and after fruit maturity, and identify biological and environmental mechanisms about fleshiness or not for fruits at maturity, using data from a survey on fruit shapes of 29760 species and one experiment involving water content measure of fruits. Results show that water content in majority of the fleshy (except for drupes and rosehips) and dry fruits increases or decreases, respectively, during fruit development i.e. prior to maturity, and the water variation patterns are determined by fruit shapes and pericarp permeability. After maturation, water loss occurs slowly at room temperature for fleshy fruits, but it is fast for most dry fruits. In general, declining fruit water content due to pericarp lignification occurring and rising pericarp permeability with the development of dry fruits in later stage of fruit development as well as water imbalance between supply and loss induced by open habitats may lead to the formation of dryness for elongated or flaky dry fruits owing to allometric growth between pedicel diameter (or fruit mass) and fruit surface area. Resulted from water balance, the emergence of fleshiness in mature fleshy fruits is attributed to slow water loss through the pericarp influenced by globular shapes (i.e. greater fruit thickness) and pericarp waxification induced by shaded habitats, or by sporoderm lignification occurring (inside the pericarp) induced by open habitats for a subset of fleshy fruits such as drupes and rosehips.