Mechanisms of speciation in Southeast Asian ant-plants of the genus Macaranga (Euphorbiaceae) associated with Crematogaster ants

生物之间的相互作用可能是驱动多样化和物种形成的关键因素。我们正在研究作为一般互惠相互作用进化的模式系统的植物与植物之间的关联。在金蚁类植物中，蚂蚁受益于寄主提供的食物和预制的巢穴，而寄主植物则受益于免受食草动物和藤蔓的侵害。古热带地区最突出的抗植物系统包括先锋树属Macaranga及其与crematogaster蚂蚁的多种联系。我们之前的工作表明，麦卡兰加种之间的遗传距离很小，表明最近的辐射。我们设想了两个可以解释这一观察结果的假设。首先，与蚂蚁的强制性共生减少了植物种群之间的基因流动，导致种群分化，最终形成异域物种。另一方面，互惠共生的蚂蚁伴侣的获得是一个关键的创新，它增强了植物伴侣在某些栖息地的适应性，从而促进了生态分化。为了验证上述第一个假设，我们将对两对猕猴桃和非猕猴桃进行比较研究，利用核微卫星标记分析(1)种群结构和基因流动程度，以及(2)基于叶绿体单倍型的历史种群差异（系统地理）。

Biotic interactions between organisms can be a crucial factor driving diversification and speciation. We are investigating myrmecophytic ant-plant associations as a model system for the evolution of mutualistic interactions in general. In myrmecophytes, the ants benefit from food and preformed nest sites supplied by their host whereas the host plants benefit from protection against herbivores and vines. The most prominent ant-plant system of the palaeotropics consists of the pioneer tree genus Macaranga and its manifold associations with Crematogaster-ants. Our previous work has shown that genetic distances between myrmecophytic Macaranga species are small, suggesting a recent radiation. We envisage two hypotheses that may account for this observation. First, the obligatory symbiosis with ants reduces gene flow among plant populations, resulting in population differentiation, and eventually allopatric speciation. Alternatively, the acquisition of mutualistic ant partners served as a key innovation which enhanced the fitness of the plant partners in certain habitats, thereby promoting ecological differentiation. To test the first of these hypotheses, we will initiate a comparative study on two pairs of myrmecophytic vs. non-myrmecophytic Macaranga species to analyse (1) population structure and the extent of gene flow using nuclear microsatellite markers, and (2) historic population divergence (phylogeography) based on chloroplast haplotypes.