Assessing ex situ genetic and ecogeographic conservation in a threatened but widespread oak after range‐wide collecting effort

Abstract

Although the genetic diversity and structure of in situ populations has been investigated in thousands of studies, the genetic composition of ex situ plant populations has rarely been studied. A better understanding of how much genetic diversity is conserved ex situ, how it is distributed among locations (e.g., botanic gardens), and what minimum sample sizes are needed is necessary to improve conservation outcomes. Here we address these issues in a threatened desert oak species, Quercus havardii Rydb. We assess the genetic, geographic, and ecological representation of 290 plants from eight ex situ locations, relative to 667 wild individuals from 35 in situ locations. We also leverage a recent dataset of >3000 samples from 11 other threatened plants to directly compare the degree of genetic conservation for species that differ in geographic range size. We found that a majority of Q. havardii genetic diversity is conserved; one of its geographic regions is significantly better conserved than the other; genetic diversity conservation of this widespread species is lower than documented for the 11 rarer taxa; genetic diversity within each garden is strongly correlated to the number of plants and number of source populations; and measures of geographic and ecological conservation (i.e., percent area and percent of ecoregions represented) were typically lower than the direct assessment of genetic diversity (i.e., percent alleles). This information will inform future seed sampling expeditions to ensure that the intraspecific diversity of threatened plants can be effectively conserved.

Biodiversity protection against anthropogenic climate change: Conservation prioritization of Castanea sativa in the South Caucasus based on genetic and ecological metrics

“…Incorporating genetic metrics into the conservation toolbox enables future risks to be defined and conservation actions to be tuned to needs in the extended horizon (Heuertz et al, 2023; Hoban et al, 2021). A host of conservation and mitigation challenges can be met by applying various genetic methods and parameters (Gougherty et al, 2021; Saeki et al, 2018; Walas et al, 2021; Zumwalde et al, 2022). Integrating genetic‐based indices with ecological metrics can make conservation strategies for populations and species more productive (Cheddadi & Khater, 2022).…”

Ex situ conservation of two rare oak species using microsatellite and SNP markers

“…DNA was extracted following a protocol described in Zumwalde et al. (2022). Details for microsatellite genotyping can be found in the Data S1: Section 1.4.1.…”

“…Despite widespread recognition that genetic diversity is essential to population persistence, many ex situ collections fall below genetic conservation targets (Hoban et al., 2020). To counteract this deficiency, a body of research has developed more comprehensive sampling guidelines for building genetically diverse ex situ collections (Bragg et al., 2021), based on empirical studies (Griffith et al., 2017; Zumwalde et al., 2022) and simulations (Bragg et al., 2021; Rosenberger et al., 2022). A majority of these studies have used microsatellites as genetic markers for determining minimum sample sizes and measuring the genetic diversity (heterozygosity, allelic richness, etc.)…”

Simulating pollen flow and field sampling constraints helps revise seed sampling recommendations for conserving genetic diversity

“…Botanic gardens and arboreta are important conservation resources, preserving species’ genetic diversity ex situ. In some cases, botanic gardens can conserve a large proportion of species’ wild genetic diversity, creating a reservoir of genetic material for future restoration efforts or to safeguard genetic material in case a species goes extinct in the wild (Hoban, 2019 ; Hoban et al, 2020 ; Zumwalde et al, 2022 ). Creating and maintaining genetically diverse collections is becoming an increasingly important goal for gardens in the changing climate (Westwood et al, 2021 ), but often requires large investments of both time and effort (see Zumwalde et al, 2022 ).…”

“…In addition, the sampling designs used in previous simulation studies have often been simplified compared to reality. Much of the research using resampling techniques based on simulated data has assumed that only one “seed” (equivalent to taking one cutting) is sampled from each plant sampled in a population (Hoban et al, 2018 ; Hoban, 2019 ; Bragg et al, 2021 ; Rosenberger et al, 2022 ; Zumwalde et al, 2022 ). It is known that sampling many unique maternal lines is the most efficient and effective method of sampling genetic diversity from a population (Hoban, 2019 ; Hoban et al, 2020 ); however, in reality, more than one seed is sampled per plant.…”