COLLABORATIVE RESEARCH: Testing a new hypothesis for global patterns in leaf form using Viburnum (Adoxaceae)

科学家们早就认识到热带和温带气候之间的叶子形状的全球模式：热带叶子有光滑的边缘，而生活在寒冷地区的植物有带齿或裂片的叶子，如桦树或枫树。这种关系是如此强烈，以至于古植物学家使用化石植物群中的叶子形状作为温度的代表，从而可以估计气候随时间的变化。但是，对于为什么存在这种关系，仍然没有机械的理解。PI假设，温带植物复杂叶缘的进化部分是由于年轻的未成熟叶片被包装成越冬芽的方式。这是受到最近芽内有效叶片折叠的数学模型以及对植物内叶片形态差异的观察的启发。荚属（Viburnum）是一个由约170种木本灌木和树木组成的谱系，在过去的5000万年里，它们多次在热带和温带森林之间转移，并表现出预期的叶子形状变化。PI将记录生长时间，叶片寿命和芽内叶包装的模式，并收集有关一组跨越热带-温带梯度的荚属物种的一套相关形态和生理特征的额外数据。他们还将继续在一个共同的花园中对约30种荚属植物进行长期的物候监测。这是一个高度合作和跨学科的项目，涉及来自其他四个国家的生物学家以及应用数学家。PI还将开发为小学生设计的教育模块，旨在弥合数学和生物学之间的差距，使用折纸和基本几何原理来理解常见的叶子形状。

Scientists have long recognized a global pattern in leaf shape between tropical and temperate climates: tropical leaves have smooth margins while plants living in cold regions have leaves with teeth or lobes, like a birch or a maple. The relationship is so strong that paleobotanists use leaf shapes in fossil floras as a proxy for temperature, allowing for estimates of climate change through time. But there is still no mechanistic understanding of why this relationship exists. The PIs hypothesize that the evolution of complex leaf margins in temperate plants results in part from the way that young, immature leaves are packed into overwintering buds. This is inspired by recent mathematical models of efficient leaf folding within buds, and by observations of within-plant differences in leaf form. Viburnum is a lineage of ~170 species of woody shrubs and trees that have shifted between tropical and temperate forests many times throughout the past 50 million years, and exhibit the expected changes in leaf shape. The PIs will document timing of growth, leaf lifespan, and patterns of leaf-packing within buds, and gather additional data on a suite of relevant morphological and physiological traits on a set of Viburnum species spanning the tropical-temperate gradient. They will also continue long-term phenological monitoring of ~30 Viburnum species in a common garden. This is a highly collaborative and interdisciplinary project, involving biologists from four other nations as well as an applied mathematician. The PIs will also develop educational modules designed for elementary school children aimed to bridge the gap between math and biology, using origami and basic geometric principles to understand common leaf shapes.