Testing adaptive radiation theory in Penstemon (Plantaginaceae)

We are very excited here at Ohio State University, Department of EEOB, to announce that we have been awarded a National Science Foundation grant to work on Penstemon (Andi Wolfe – principal investigator, Laura Kubatko – co-principal investigator). For the next three years or so, we will be doing a study to investigate why this beautiful and species-rich genus has diversified so rapidly across North America. We’ll be using next-generation sequencing approaches (25 to 100 genetic loci) to estimate the phylogeny for up to 90% of all the species of Penstemon. Given that Penstemon has 280 or more described species, and there are likely many more yet to be discovered, this is a huge project! To handle such a large amount of data, we’ll be working with new methods of analyses for phylogeny reconstruction, developed by Laura Kubatko’s group. We’ll also be investigating the patterns of hybridization throughout the genus by developing new modeling methods. My lab will do the field work, morphometric, ecological analyses, and next-gen sequencing projects. Laura Kubatko’s lab will be doing all of the analytical and modeling work for phylogeny reconstruction and examining patterns of hybridization in the phylogenetic tree. If you would like to know more about the technical aspects of the project, I will include our project summary from the grant proposal below.

Because this project requires a lot of sampling, we would welcome collections of Penstemon. We have nearly 75% of the genus sampled from work done over the past couple of decades, but it’s always a good thing to renew DNA stocks and to have multiple populations sampled. Species we really need include: P. arenarius, P. australis, P. brevisepalus, P. compactus, P. concinnus, P. deamii, P. deaveri, P. distans, P. duchesnensis, P. filisepalis, P. floribundus, P. flowersii, P. gentry, P. glaucinus, P. goodrichii, P. grahamii, P. guadalupensis, P. hintonii, P. kingii, P. kralii, P. marcusii, P. miser, P. mohinoranus, P. moriahensis, P. moronensis, P. nanus, P. navajoa, P. occiduus, P. pahutensis, P. parviflorus, P. parvus, P. patricus, P. pseudoparvus, P. pudicus, P. pumilis, P. rhizomatosus, P. rotundifolius, P. seorsus, P. skutchii, P. sudans, P. tenuiflorus, P. tepicensis, P. tiehmii, P. tracyi, P. triflorus, P. vizcainensis, and P. wardii. I fully expect us to get many of these species, including many rare and narrow endemics, from field work this season and next year. However, if you have locality information, seed, or collections for any of the species on this list, I would very much like to hear from you.


Project summary for Testing adaptive radiation theory in Penstemon (Plantaginaceae):

Overview. Adaptive radiation theory (ART) predicts an increase in speciation rates resulting from adaptations in response to ecological opportunity, and that speciation rates are initially high, but decrease as ecological niches fill or extinction rates increase. Though several iconic groups of animals have served as test cases for ART, relatively few plant studies have focused on testing ART. Next-gen sequencing approaches offer new insights for ART, but handling the large volumes of data associated with collecting genomic data has been a technological challenge. In this proposed research ART will be tested in Penstemon, a large genus endemic to North America, using a phylogenetic framework derived from next-gen targeted amplicon sequencing of multiple loci. A multi-species coalescent approach will be used for estimating a species tree from multi-locus data, and new methods of analyses will be developed to handle data sets with both many taxa and many loci. The species tree inferred will be used to examine rates of species diversification across the genus, with specific attention to the question of whether clades exhibit patterns consistent with those predicted by ART. Morphological characters, ecological habitats, seed germination requirements, incidence of hybridization, and geographical data will be analyzed to determine if there are key innovations and/or ecological opportunity that may explain differences in speciation rates across the genus. Additionally, new methods of analyses will be developed for detecting patterns of hybridization in a genus that has a rapid rate of diversification.

Intellectual Merit. Penstemon has the potential to become an iconic model system for studying adaptive radiation theory. The genus has ~280 species comprising six subgenera divided into 12 sections and 23 subsections. Several studies over the past century have suggested that Penstemon is a relatively young genus and that species diversification has been driven by ecological opportunity for habitat specialization and shifts in pollinator specificity. Current phylogenetic hypotheses are from limited data (ITS and cpDNA sequences) that are in conflict and have been insufficient to resolve relationships among taxonomic groups or species. The combination of next-gen sequencing, new phylogenetic methods, and statistical modeling approaches will enable a robust assessment of ART in this morphologically diverse genus.

Broader Impacts. The phylogenetic framework developed for our study will benefit the broader scientific community for studying the evolution of morphological and ecological traits. For example, pollination ecologists have been awaiting a robust and well-resolved phylogeny in Penstemon to better study shifts in pollinator specificity from insect- to bird- adapted morphologies. The methods we develop for handling large data sets for phylogenomics will also benefit the research community; all software developed will be made freely available on the website of co-PI Kubatko. Another website dedicated to tutorials of methods will be one result of this proposed research.

Penstemon is rapidly becoming an important horticultural species, especially in water-limited areas of the southwest; there is a large amount of interest for genetic markers to use in developing new cultivars via marker-assisted breeding. We will make primer sequences for our genetic loci available to the broader research community via publications and the development of a resource website to facilitate dissemination of information. Given the horticultural interest in Penstemon, the USDA Ornamental Plant Germplasm Center (OPGC) at OSU has been acquiring germplasm in order to provide seeds and cuttings to plant breeders and wildflower garden enthusiasts. We will share locality data with OPGC to facilitate their seed collecting efforts, and will contribute to their germplasm collection. We will also provide digital images of species, slide presentations, and seminar resources to OPGC, the American Penstemon Society, and native plant societies whose members share an interest in penstemons. Educational outreach via public lectures about our research efforts and weblog posts about Penstemon (e.g., Penstemon of the Day series at https://wolfelab.wordpress.com) will be a priority. Student mentoring is a key element of our proposed research. We are particularly focusing our efforts on building a math/bio community of students where statistical modeling is a key element for addressing systematics questions. Mentoring will include graduate and undergraduate students as a collaborative cadre focused on the research proposed for this study. Two graduate students (one from Statistics, one from EEOB) and three undergraduate students will be trained in cross-disciplinary studies incorporating phylogenetics, statistical modeling, and evolutionary biology