Evolution in the genus Baccharis L. - analysis of a homoploid hybrid complex based on genomic and chemical diversity

• Applicants: Professor Dr. Frank Hellwig; Dr. Tobias Gerhardt Köllner
• Subject Area: Evolution and Systematics of Plants and Fungi ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 445708872

Hybridization has been considered to play an important role in biological evolution, especially in plants. While in most cases hybrid sterility is overcome by polyploidization, there are also examples for plant species groups that remain at the ploidy level of the parental species. This enables the hybrids to backcross with one or both parents eventually forming dense hybrid swarms. An example of such a homoploid hybrid complex is the genus Baccharis L. (Asteraceae) in Chile, comprising 16 species of evergreen shrubs which are dioecious and insect-pollinated. The plants contain a multitude of chemical compounds including terpenes and flavonoids that are biologically active, for example in defense against herbivores or pathogens. The taxonomy of this group has been investigated thoroughly leading to the description of numerous hybrid taxa interconnecting supposedly pure species. However, phylogenetic relationships between the taxa remain unresolved and hybridization events are hypothesized on the base of morphology alone.Technical and methodological advances over the last years have opened up new possibilities to disentangle the intricate structure and evolution of hybrid complexes like Baccharis. In this project we will apply next generation sequencing techniques using accumulated sequence information sampled from the whole plant genome to reconstruct the evolutionary history involving a group of hybridizing species in Baccharis in their natural habitats in Chile. Evolutionary changes will be discussed in the context of climate change in the past and considering vegetation transformation by humans during the last centuries. In order to understand the adaptive value of chemical variants, we will investigate the specialized metabolism of Baccharis hybrids. In particular we will analyze volatile compounds and non-volatile polar metabolites in hybrid swarms to elucidate how hybridization affects the composition of specialized compounds. Fitness consequences of hybridization will be studied in situ and in an experimental population at Jena where we also will perform feeding experiments. The project brings together two working groups from the Max Planck Institute for Chemical Ecology and the Friedrich Schiller University of Jena with expertise in investigations on ecological and evolutionary aspects of plant specialized metabolism, classical taxonomy, molecular phylogeny, and molecular population genetics.

• DFG Programme: Research Grants