Pollination ecology and genetic population structure of three species of cacao (Theobroma spp.) in Bolivia

• Applicant: Professorin Dr. Isabell Hensen
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2008 to 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 82531614

Tropical rainforest tree species are characterized by low population densities, with great distances between conspecific individuals. This spatial distribution has consequences for gene flow, especially for the intertree movement of pollinators. In view of ongoing forest fragmentation, knowledge on gene flow is elementary for comprehending the reproductive success in tropical tree species. Here, we propose to use three understorey species of Theobroma (cacao) in northern Bolivia as a model system to compare pollinator assemblages, mating systems, and patterns of gene flow in wild and cultivated populations, using plots of different tree density. We assume that the pollination ecology of Theobroma species differs between species as well as between wild and cultivated populations, and that the spatial and temporal distribution of pollinators is mainly determined by climatic factors, by the number of simultaneously open flowers, and by tree population density. We further hypothesize that the ratio between selfing and outcrossing varies in differently dense populations, and that higher population density, artificial pollination and higher genetic distinctness enhance pollination success and fruit set. The population genetic structure will probably be moderate, due to the dependence on animals for both, pollination and seed dispersal. Besides field studies encompassing pollinator capture studies and fruit set experiments, we will use direct and indirect molecular methods for assessing gene flow such as assessment of spatial genetic structure and parentage analysis to follow these assumptions. Our results are of general interest for understanding the evolution of mating systems in tropical forest ecosystems.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Participating Person: Professor Dr. Michael Kessler