Ex Situ Conservation of Large and Small Plant Populations Illustrates Limitations of Common Conservation Metrics

Abstract

Premise of research. Ex situ plant conservation can be improved through genetic analysis. One area of interest is the relative value of conserving smaller or larger populations and how sampling strategies for these might differ. Current practice emphasizes collecting large sample sizes from some populations and limiting sampling from others and aims for the capture of allele diversity exceeding predetermined thresholds at the species level. Evaluating how well botanic garden collections can capture the genetic diversity of populations of different sizes can help refine guidance on conservation efforts. Methodology. A model species, Pseudophoenix sargentii (Arecaceae), was chosen for its disjunct and insular range, variation in population size, and presence in collections. We compared 123 in situ plants from three discrete island populations with 94 ex situ conservation specimens via 10 microsatellite markers. Comparison of allelic diversity among the wild populations and collections allowed for the evaluation of genetic capture. Pivotal results. Genetic distance analysis, fixation indexes, and Bayesian clustering analysis show discrete in situ geographic structure and close affinity between ex situ collections and in situ source populations. Yet collections from just the largest population met the Global Strategy for Plant Conservation Target 9 threshold for conservation success for that source population, for other smaller populations, and for all populations together. Conclusions. Percent of genetic capture thresholds may need revision, as such thresholds overlook important diversity. Efficient genetic capture is maximized by emphasizing unique maternal lineages and limiting half-siblings in a collection, but this selectivity must be balanced against the need for redundancy in living collections. Large and small populations each contribute to meeting genetic diversity goals. We recommend that botanic gardens and their networks develop conservation priorities based on genetic diversity and resources, carefully consider existing thresholds for conservation success, define metrics for ex situ conservation goals, and integrate analysis into ex situ conservation efforts.