二型叶棘豆种内单复叶型多态性的演化研究

Leaf shape is one of the most variable plant traits. To understand the evolutionary drivers of diversification in leaf shape and the ecological significance therein has been of continuing interest for many years. Although leaves can be basically categorized as simple and compound, naturally occurring leaf shape polymorphism of simple and compound leaves has seldom been described. Also, direct evidences are comparatively rare to demonstrate that leaf shape is actually adaptive...In Inner Mongolia of China, Oxytropis diversifolia (Fabaceae) exhibit simple-compound leaf shape polymorphism within species. We aim to use this species, and also use two closely related species with only simple or compound leaves as control, to characterize the evolutionary forces shaping leaf shape variation. The project consists of the following three parts: firstly, leaf shape variation of individuals from different populations will be assessed in a common environment, to determine whether the variation is genetic. Secondly, neutral genetic variation across populations will be measured for both chloroplast fragments and nuclear microsatellite loci. The extent of differentiation in leaf shape will be compared with that of neutral loci, to determine whether leaf shape variation is subject to selection. Thirdly, microhabitat at local scale and macrohabitat at coarse scale will be investigated, in order to find the important ecological factors shaping leaf shape variation across space, and also to determine the pattern of leaf shape divergence therein. Upon the above studies, we’ll better understand the evolutionary forces driving phenotypic variation of simple-compound leaves, and how plants evolve in dry grassland/semi-desert regions.

叶型是植物最富于变化的性状之一，阐明叶型多样化的演化动力和叶型的生态重要性是多年来进化生态学者持续感兴趣和关注的问题。尽管植物叶可以基本地分为单叶和复叶，具有单复叶型多态性的物种目前还少有描述和研究，对叶型变异潜在的适应性也缺乏直接的证据。..分布于内蒙古地区的二型叶棘豆具有种内单复叶型多态性，本项目将以此种为对象，以种内只有单叶或复叶的两个近缘种为对照，研究植物单复叶型变异的演化因素。项目包括三个内容：1）通过同质种植，说明单复叶型变异的可遗传性；2）通过调查居群间中性遗传变异（叶绿体基因片段和核基因微卫星位点），并与叶型变异相比较，研究叶型变异可能受到的自然选择；3）通过微生境与大生境调查，找出影响单复叶型空间异质分布的重要环境因子，探讨相关的叶型分化模式。本研究有助于阐明植物单复叶型变异的演化动力，也可为理解干旱草原荒漠地区植物的演化提供依据。

特殊环境下植物表型的适应性演化是植物进化生态学研究关注的重要科学问题。叶型是植物最富于变化的性状之一，由于叶的功能重要性，学界普遍认为叶型变异会产生重要的生理生态影响，所以叶型变异很有可能是植物对不同环境的适应，但是一直以来叶型变异潜在的适应性缺乏直接的进化生物学证据。. 本项目以分布于内蒙古地区，具有种内单复叶型多态性的二型叶棘豆为研究对象，以种内只有单叶或复叶的两个近缘种为对照，研究植物单复叶型变异的演化因素。首先我们通过同质种植实验说明了种内和种间叶型变异的可遗传性。再次，我们发现二型叶棘豆的居群表型由西向东出现梯度群分化，而中性分子标记（叶绿体片段和核基因微卫星位点）显示了较小的遗传分化且无明显的居群遗传结构，说明了自然选择是单复叶型梯度群形成的主要驱动力。进一步的环境相关分析表明这种自然选择很可能主要由空间异质的气候因子——年降水量和温度季节性导致。这些结果为叶形变异的适应性假说提供了直接的证据，也为理解干旱草原荒漠地区植物的演化提供了依据。