Collaborative Research: Replicated evolution of leaf form in a neo-tropical radiation of Viburnum (Adoxaceae)

关于生物多样性的起源，包括新物种的起源，仍有许多未知之处，但这些知识对于理解进化和预测对快速环境变化的反应至关重要。本研究将调查一个引人注目的案例，在一组树木和灌木（Viburnum）中，快速分化似乎已经反复发生，成为两种完全不同的植物形式。这些植物叶片的主要差异似乎是由于适应了环境变量略有不同的邻近森林类型。这一过程在整个新世界热带地区的几个不同山区的明显复制，为严格测试快速生态物种形成模型提供了难得的机会。将在墨西哥不同山区对邻近植物种群进行详细研究，目的是确定有利于这些叶片性状快速进化的环境因素和种群内变异的性质。利用这些物种之间的自然杂交，也应该有可能确定这些关键植物特征的基因。这些研究将产生对物种形成的一般见解，也将产生对整个开花植物中区分相关物种的叶片特征的适应性意义。这项研究将与墨西哥科学家合作进行，并将涉及多名本科生和研究生。外联活动的目的是促进美国和墨西哥参与者之间的互动。该项目特别侧重于了解墨西哥东部和南部山区三对物种形成的驱动因素。每对中的两个种在叶的大小和形状（大而圆对小而椭圆），叶缘（齿状对光滑）和叶的短柔毛（浓密有毛对缺乏毛）上有显著的不同。这项研究将集中于量化单个植物内部、种群内部和物种对之间的变化，并确定它们的森林栖息地之间的非生物和生物因素的差异。关于叶片变量的适应性值的假设将使用相邻栖息地之间的样带和互惠移植实验进行测试。在长期受到土著农业实践干扰的地区，广泛的杂交产生了各种各样的中间叶形式。对这些杂交群体进行分子分析，应该能够鉴定出导致叶片形态差异的主要基因。本项目由国际科学与工程办公室共同资助。

Much remains unknown about the genesis of biological diversity, including the origin of new species, yet such knowledge is critical to understand evolution and to make predictions about responses to rapid environmental change. This research will investigate a striking case in a group of trees and shrubs (Viburnum) in which rapid differentiation appears to have occurred repeatedly into two radically different plant forms. Major differences in the leaves of these plants appear to have resulted from adaptation to adjacent forest types that differ subtly in environmental variables. The evident replication of this process in several different mountain regions throughout the New World tropics, provides a rare opportunity to critically test a model of rapid ecological speciation. Detailed studies of adjacent plant populations will be carried out in different mountain regions in Mexico with the aim of identifying the environmental factors and the nature of the variation within populations that have favored the rapid evolution of these leaf traits. It should also be possible to identify genes that underlie these key plant characteristics by taking advantage of natural hybridization between these species. These studies will yield general insights into speciation but also into the adaptive significance of the leaf traits that differentiate related species throughout the flowering plants. This research will be carried out in collaboration with Mexican scientists and will involve multiple undergraduate and graduate students. Outreach activities have been designed to foster interactions between participants from the United States and Mexico. This project focuses specifically on understanding the drivers of speciation in three species pairs in the mountains of Eastern and Southern Mexico. The two species in each pair differ dramatically in leaf size and shape (large and round versus small and elliptical), in leaf margins (toothed versus smooth), and in leaf pubescence (densely hairy versus lacking hairs). The research will focus on quantifying variation within individual plants, within populations, and between the species pairs, and on determining the abiotic and biotic factors that differ between their forest habitats. Hypotheses on the adaptive value of the leaf variables will be tested using transects between adjacent habitats and a reciprocal transplant experiment. In areas that have long been disturbed by indigenous agricultural practices, extensive hybridization has resulted in a wide array of intermediate leaf forms. Molecular analyses of these hybrid swarms should allow the identification of the major genes that underlie differences in leaf form. This project is jointly funded with the Office of International Science and Engineering.