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

生物体之间的生物相互作用可能是推动多样化和物种形成的一个关键因素。我们正在研究蚁植蚂蚁植物协会作为一个模型系统的互惠互动的演变一般。在蚁穴植物中，蚂蚁受益于宿主提供的食物和预先形成的巢穴，而宿主植物受益于对食草动物和藤蔓的保护。古热带地区最突出的蚂蚁-植物系统包括先锋树属血桐及其与Crematogaster-ants的多种联系。我们以前的工作表明，蚁生血桐属物种之间的遗传距离很小，这表明最近的辐射。我们设想了两种可能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。另外，收购互惠蚂蚁合作伙伴作为一个关键的创新，提高了适应性的植物合作伙伴在某些栖息地，从而促进生态分化。为了验证这些假设中的第一个，我们将启动对两对myrmecophytic与非myrmecophytic血桐物种的比较研究，以分析（1）人口结构和基因流的程度，使用核微卫星标记，和（2）历史人口分歧（地理学）的基础上叶绿体单倍型。

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.