Taxonomic similarity does not predict necessary sample size for ex situ conservation: a comparison among five genera

Authors: HOBAN, SEAN - Morton Arboretum; CALLICRATE, TAYLOR - Chicago Zoological Society; CLARK, JOHN - San Diego Zoo; DEAN, SUSAN - Northwestern University; DOSMANN, MICHAEL - Harvard University; FANT, JEREMIE - Chicago Botanical Garden; GAILING, OLIVER - University Of Gottingen; HAVENS, KAYRI - Chicago Botanical Garden; HIPP, ANDREW - Morton Arboretum; KADAV, PRIYANKA - Michigan Technological University; KRAMER, ANDREA - Chicago Botanical Garden; LOBDELL, MATTHEW - Morton Arboretum; MAGELLAN, TRACY - Montgomery Botanical Center; MEYER, ABBY - Botanic Gardens Conservation International; Pooler, Margaret; SPENCE, EMMA - Morton Arboretum; THOMPSON, PATRICK - Auburn University; TOPPILA, RAAKEL - University Of Delaware; WALSH, SEANA - National Tropical Botanical Garden (NTBG); WESTWOOD, MURPHY - Morton Arboretum; WOOD, JORDAN - Illinois Natural History Survey; GRIFFITH, PATRICK - Montgomery Botanical Center

Submitted to: Proceedings of the Royal Society. B. Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2020
Publication Date: 4/30/2020
Citation: Hoban, S., Callicrate, T., Clark, J., Dean, S., Dosmann, M., Fant, J., Gailing, O., Havens, K., Hipp, A., Kadav, P., Kramer, A., Lobdell, M., Magellan, T., Meyer, A., Pooler, M.R., Spence, E., Thompson, P., Toppila, R., Walsh, S., Westwood, M., Wood, J., Griffith, P. 2020. Taxonomic similarity does not predict necessary sample size for ex situ conservation: a comparison among five genera. Proceedings of the Royal Society B. 287:20200102. https://doi.org/10.1098/rspb.2020.0102.
DOI: https://doi.org/10.1098/rspb.2020.0102

Interpretive Summary: Currently, 14,300 plant species are classified as threatened with extinction including 63% of cycads and 40% of conifers, although most plant species have not been assessed. Living collections of plants held in botanic gardens, arboreta, and seed banks help safeguard species from extinction as well as inspire and educate the public and provide material for scientific study and ecological restoration. However, with limited resources, it is challenging to capture the maximum amount of genetic diversity in as few individuals as possible. A team of scientists from botanic gardens and universities examined data from five plant genera to determine if standard collection sizes could be determined that could then be used for scientifically grounded recommendations for collecting and conserving plant genetic resources. The team used genetic datasets and resampling algorithms to determine appropriate collection size in 11 taxa from Hibiscus, Magnolia, Pseudophoenix, Quercus, and Zamia. All are relatively long-lived, threatened species whose seeds cannot be seedbanked due to inherent seed physiology or ecological factors. The team found that the percentage of genetic diversity currently conserved in collections varies among taxa, from 40 to 95%. Most taxa are well below genetic conservation targets. Resampling datasets showed that ideal collection sizes vary widely even within a genus, although across taxa,the minimum collection size to achieve genetic conservation goals is within one order of magnitude. The study determined that current collections are suboptimal in that they could remain the same size yet capture twice the genetic diversity with improved sampling design. Strategies for optimizing collection design to maximize diversity are also presented.

Technical Abstract: Effectively conserving biodiversity with limited resources requires scientifically informed and efficient strategies. Guidance is particularly needed on how many living plants are necessary to conserve a threshold level of genetic diversity in ex situ collections. We investigated this question for 11 taxa across five genera. In this first study analyzing and optimizing ex situ genetic diversity across multiple genera, we found that the percentage of extant genetic diversity currently conserved varies among taxa, from 40 to 95%. Most taxa are well below genetic conservation targets. Resampling datasets showed that ideal collection sizes vary widely even within a genus: one taxon typically required at least 50% more individuals than another (though Quercus was an exception). Still, across taxa, the minimum collection size to achieve genetic conservation goals is within one order of magnitude. Current collections are also suboptimal: they could remain the same size capture twice the genetic diversity with improved sampling design. We term this deficiency the “genetic conservation gap.” Lastly, we show that minimum collection sizes are influenced by collector priorities regarding the genetic diversity target. In summary, current collections are insufficient (not reaching targets) and suboptimal (not efficiently designed), and we show how improvement can be made.