Milkweeds (the genus Asclepias) are beautiful plants that are well known and commonly planted for their ability to attract butterflies. There are 135 species of milkweed in North America that have all originated fairly rapidly. This project will use genomic sequencing technology to investigate how the species are related to each other. DNA sequences will be obtained from complete chloroplast genomes and 10 nuclear genes from two or more samples of each species. The goal is to achieve a species level phylogeny of a large, rapidly radiating genus.
The resolution of systematic relationships among milkweed species will help to improve the classification of the genus. Furthermore, these results will provide a robust foundation for studies of milkweed floral diversity, pollination biology and biogeography. Milkweeds have long served as a model system for the evolution of plant defenses against herbivory, and results from this research will contribute to a better understanding of how plants co-evolve with their pests. The methods developed here achieve a savings in cost, time, and effort beyond any previously attained in comparative genomics, and will be directly applicable to phylogenetic, population genomic and ecological genomic studies of animals, fungi and plants. A post-doctoral associate and three undergraduate students will be trained, and two workshops designed to introduce plant systematists to genomic sequencing approaches will be conducted at the annual Botany meetings in 2010 and 2011.
The goal of this project was to sequence genomes and use those data to obtain more accurate estimates of the evolutionary relationships among the North American species of milkweed. Milkweeds are best known as the host of the monarch butterfly, but they also represent an exceptionally diverse group of plants with unique adaptations to insect pollinators and herbivores. We sequenced the chloroplast genomes from 171 individuals representing 105 species of the milkweed genus. We also sequenced the nuclear genome of the common milkweed, Asclepias syriaca. Analyzing the chloroplast genomes, we discovered a rare evolutionary event: the transfer of part of the mitochondrial genome into the chloroplast genome of the common milkweed. We also determined when this occurred in the history of the milkweed family, and developed a hypothesis for how this occurred. Using data from the nuclear genome, we identified 768 genes that were useful for the analysis of evolutionary relationships among milkweed species. Furthermore, we developed a novel approach for efficiently sequencing hundreds of genes in dozens of species. This method has the potential to be widely utilized by plant systematists. We also organized workshops at the annual meetings of the Botanical Society of America in 2010, 2012 and 2013 to introduce over 150 plant scientists to the genome sequencing methods that are being utilized in our research.
