Collaborative Research: Genetic diversity, resistance genes, and negative density dependence in tropical tree seedling dynamics

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Tropical forests are famous for their high diversity, as well as the large number of rare species they harbor. Recent studies have found that, compared to common species, rare tropical tree species suffer more from pathogens that are specialized to a single host species that then spread rapidly through dense patches of seedlings of that single host. This research will test the novel hypothesis that rare species are more strongly impacted by host-specific pathogens because they have lower diversity of resistance genes at the population level, such that all their seedlings will be susceptible to the same suite of pathogens, promoting rapid pathogen spread and increasing mortality rates. This hypothesis will be tested using experimental greenhouse and field studies, combined with genetic analyses that will quantify the diversity of resistance genes for rare and common tree species in lowland tropical forest on Barro Colorado Island, Panama. Computer simulations will also be used to examine whether the measured differences in resistance gene diversity would impact infection levels, mortality rates and local abundance of tree species. Results of this study will improve understanding of plant-pathogen interactions, with potential applications for agriculture and horticulture (e.g. increasing pathogen resistance in crops). Hands-on training in cutting-edge genetic techniques would be provided to a wider audience through a summer workshop for students and faculty. This study will be the first to obtain large transcriptome datasets from a tree community and will provide gene sequence data that will be informative for future studies of genetic diversity in tropical forests. Examination of the effects of resistance gene diversity on forest dynamics will bridge the gap between molecular evolution studies that indicate ongoing selection for multiple resistance genes at many loci, and how this diversity functions in nature. Furthermore, this study is likely to bridge competing theories for tropical plant diversity by providing a genetic explanation for why rare tree species are more strongly controlled by their species-specific enemies, while simultaneously supporting dispersal limitation as a feature determining which species are locally dominant. Ultimately, the study should elucidate whether local rarity restricts local genetic diversity, which in turn reinforces local rarity, a cycle that can be escaped only by recruitment of new alleles via long-distance pollen or seed movement. Demonstrating such a coupling between the ecological and genetic features of populations would bring new perspectives and avenues for theoretical advances in evolution and ecology. The project will provide research experiences for undergraduate and graduate students, as well as a postdoctoral researcher.