Genetic Diversity Assessment of Ex Situ Collections of EndangeredQuercus hinckleyi

Abstract

Premise of research. Conservation of imperiled plant species can benefit from ex situ collections, including the living collections of botanic gardens and arboreta. Such living collections should strive to capture and maintain the genetic diversity found in the remaining wild populations. Ex situ collections may also harbor genetic variability that has been lost from wild populations. Quercus hinckleyi is an extremely rare (International Union for Conservation of Nature and Natural Resources [IUCN] Critically Endangered) oak known from a few sites in Presidio County, Texas. It is the only native US oak protected under the Endangered Species Act. Here we evaluate the genetic variation of the Q. hinckleyi ex situ metacollection relative to that of the remnant in situ population. Methodology. We apply microsatellite genotyping to Q. hinckleyi sampled from plants growing in ex situ collections (N p 22, from nine gardens) and compare the results with genetic studies of the in situ population. We compare allelic diversity, genotypic diversity, and population structure. Pivotal results. The ex situ metacollection is small but has high allelic diversity and captures about 57% of the allelic diversity of the wild population. Ex situ plants contain 22 new alleles that contribute 13% of the species' total allelic diversity. All ex situ individuals have unique genotypes, none of which were found in situ, and thus they comprise 15% of the species' genotypic variation. The ex situ plants align with only one of three genetic clusters identified in situ, demonstrating an important gap in the ex situ metacollection. Conclusions. The ex situ collection of Q. hinckleyi, while small, is genetically diverse and provides additional allelic and genotypic diversity not currently existing in situ. However, a significant portion of genetic diversity is lacking from ex situ plants, with the metacollection likely derived from only one of the in situ clusters. Collecting seed from the other clusters is a high priority.

Quercus Conservation Genetics and Genomics: Past, Present, and Future

“…Quercus hinckleyi is a Critically Endangered species with an extremely limited distribution in Texas, USA. Population genetic studies have examined clonality, diversity and population structure [18], hybridization [55], and genetic diversity assessment of in situ and ex situ populations [54]. Important for conservation, Backs et al [18] reported a high level of clonality at some sites, with the number of genetically unique individuals being substantially lower than previously assumed from population counts.…”

“…Desiccation is part of the standard protocol of conventional seed-banking [101][102][103][104]. Conservation of living oaks in ex situ collections can be constrained by space limitations, long generation times, and their proclivity to hybridize [54]. A recent paper by Backs et al [54] reported that ex situ collections of Q. hinckleyi were likely sampled from only one of the remaining in situ genetic clusters and missed much of the in situ diversity.…”

“…Conservation of living oaks in ex situ collections can be constrained by space limitations, long generation times, and their proclivity to hybridize [54]. A recent paper by Backs et al [54] reported that ex situ collections of Q. hinckleyi were likely sampled from only one of the remaining in situ genetic clusters and missed much of the in situ diversity. The study of Quercus georgiana, Q. oglethorpensis, and Q. boyntonii mentioned above reports that while common alleles are well preserved in ex situ collection, low frequency and rare alleles are not [39].…”

Assembling genetic structure of Gardenia remyi, a critically endangered tree endemic to the Hawaiian Islands

“…A strategy that has proven especially useful for the conservation of very rare plant species is to utilize ex situ collections where specimens are grown in conservation collections and stored in seed banks (Backs et al, 2021; Foster et al, 2022; Wolkis et al, 2021). However, a major challenge for ex situ collections is a lack of information about wild source populations as well as capturing the genetic variation of their origin (Backs et al, 2021; Maunder et al, 2001). Previous studies provide examples of critically endangered Hawaiian endemic plants, such as Brighamia insignis A.…”