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

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Tropical forests are known for their high biological diversity, and this is partly due to the large numbers of rare species they contain. One reason for rarity in tropical trees seems to be high rates of death from diseases that spread between individuals of the same species. When a seedling of a rare species is surrounded by neighbors of the same species, its risk of dying from pathogens is much higher than that of a seedling of a common species surrounded by neighbors of that species. This project will test the new hypothesis that rarity goes along with low resistance to disease because having just a small number of individuals of a species leads to also having a low diversity of the genes that are responsible for disease resistance. The hypothesis will be tested through collaboration between scientists at the Smithsonian Institution and Pennsylvania State University. Plant tissue will be collected from related pairs of rare and common species of tropical trees at the Smithsonian's Tropical Research Institute in Panama. The tissue will be shipped to Pennsylvania, where a new technique in molecular genetics known as next generation transcriptome sequencing will be used to quantify the overall and resistance gene diversity of each species. Back in Panama, experiments in the forest will test whether enhancing cross-pollination between trees can increase the genetic diversity of their offspring and give them greater resistance to disease and chances of survival.This study will provide useful insights into how the abundance of a species can shape its ability to resist disease. Knowing this will help us understand why some species are rare while others are common, and help forest managers make more informed decisions. This project will be the first to obtain a large collection of resistance gene sequences from trees, information that can used in future studies of genetic diversity in agricultural and horticultural plants. The project will also provide training for students and early career biologists in both the United States and Panama.