Conserving Genetic Diversity of Southeastern Oaks and Magnolias in Botanic Gardens: How Much is Needed?

Dr. Sean Hoban, The Morton Arboretum, Taylor Callicrate, Species Conservation Toolkit Initiative, Chicago Zoological Society, Susan Deans, Plant Biology and Conservation Program, Northwestern University, Michael Dosmann, The Arnold Arboretum of Harvard University, Jeremie Fant, Chicago Botanic Garden, Oliver Gailing, University of Göttingen, Kayri Havens, Chicago Botanic Garden, Andrew Hipp, The Morton Arboretum, Priyanka Kadav, Michigan Technological University, Andrea Kramer, Chicago Botanic Garden, Matthew Lobdell, The Morton Arboretum, Tracy Magellan, Abby Meyer, Botanic Gardens Conservation International, Emma Spence, Center for Tree Science, The Morton Arboretum, Patrick Thompson, Auburn University Raakel Toppila, Seana Walsh, National Tropical Botanical Garden, Murphy Westwood, The Morton Arboretum, Jordan Wood, Illinois Natural History Survey, M. Patrick Griffith, Montgomery Botanical Center

Ex situ collections such as botanic gardens inspire and educate the public, provide material for scientific study, and produce material for ecological restoration. The challenge for an efficient and effective collection is safeguarding high genetic and ecological diversity in as few samples as possible, due to the relatively small resources available for conservation. A botanic garden might have resources to maintain a few to a few hundred plants of priority species in conservation collections, but not the thousands that seed banks can preserve. Providing scientifically grounded recommendations for the number of individuals that need to be conserved, and how to collect from the wild and manage collections over time, is a pressing need. Previous work using case studies and modeling of important biological traits has established the fact that some species must be sampled differently, and that widely used standard sample sizes might not be optimal practice for capturing the maximum diversity. We present here a comparative study of ex situ gene conservation in three southeastern oaks (Quercus georgiana, oglethorpensis and boyntonii) and two magnolias (M. pyramidata and asheii). Specifically, we use genetic datasets and resampling algorithms to: quantify how much genetic diversity has been captured in a global network of botanic garden collections currently, resample the wild population genetic datasets to determine how much genetic diversity could be captured by varying sample sizes, determine minimal sampling needed to capture 70% and 95% of the genetic diversity, and use a diminishing returns method to calculate optimal stopping points- when additional collection effort no longer provides sufficient gains. Between 62 and 72% of genetic diversity is currently safeguarded for the oaks, and about 80% is conserved for the magnolias. The recommended collection size depends on key decisions by curators about the type of genetic diversity that is valued, but may range from approximately 50 to 200 individuals. We hope that these findings motivate future seed collections from wild provenances for botanic garden collections and stimulate discussion on ex situ gene conservation goals and outcomes.