Spatial-temporal evolution of Macaranga ant-plant lineages (Euphorbiaceae) in Southeast Asia

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A recent proliferation of studies on the evolution of ant-plant mutualisms underlines the unbroken interest in this fascinating phenomenon. The most specialized and efficient form of protective ant-plant associations is myrmecophytism. In this symbiosis, the plants provide their partner ants with nesting space and food, while the ants protect their host plants against herbivores, pathogens and encroaching vegetation. Myrmecophytism has evolved more than 150 times independently during the evolution of higher plants. To understand the ecological and evolutionary circumstances that promote the origins and losses of myrmecophytic traits, well sampled and highly resolved phylogenies of the myrmecophytic plant lineages and their relatives are needed. Poor phylogenetic resolution has been observed in many myrmecophytic lineages that were analyzed by Sanger sequencing of traditional marker loci, probably owing to the recent origin (< 15 million years) of the respective clades. In this project we will use, for the first time, next generation sequencing technology (genotyping-by-sequencing, GBS) to resolve phylogenetic relationships among and within myrmecophytic lineages of the Southeast Asian ant-plant genus Macaranga. While many Macaranga species facultatively attract ants, about 30 species from western Malesia (comprising Borneo, Sumatra, the Malay Peninsula, and surrounding islands; collectively Sundaland) live in obligate symbiosis with nine species of Crematogaster ants. Based on a GBS-derived analysis of 234 specimens including almost all myrmecophytic Macaranga species and their non-myrmecophytic relatives, we will reconstruct the temporal-spatial evolution of myrmecophytism in the group. In the first part of the project, we will further elucidate when, where and under which circumstances morphological traits associated with myrmecophytism have been gained (and lost), and we will test the hypothesis that myrmecophytism enhanced diversification and speciation in Macaranga. In the second part of the project, general aspects of Sundaland biogeography will be addressed by a GBS-based, comparative phylogeographic approach including between 30 and 50 specimens each from five widely distributed species with different ecological requirements and relationships with ants. We specifically aim to understand how past climatic and geographic settings in Sundaland influenced the population structure and gene flow patterns of western Malesian Macaranga.