AUTHOR=Edwards Christine E. , Bassüner Burgund , Williams Brigette R. 

TITLE=Population Genetic Analysis of the Threatened Plant Leavenworthia exigua var. laciniata (Brassicaceae) Reveals Virtually No Genetic Diversity and a Unique Mating System

JOURNAL=Frontiers in Conservation Science

VOLUME=3

YEAR=2022

URL=https://www.frontiersin.org/journals/conservation-science/articles/10.3389/fcosc.2022.831085

DOI=10.3389/fcosc.2022.831085

ISSN=2673-611X

ABSTRACT=<p><italic>Leavenworthia</italic> (Brassicaceae) has served as a model group for investigating the evolution of mating systems in plants, yet several <italic>Leavenworthia</italic> species remain understudied. One such taxon is <italic>Leavenworthia exigua</italic> var. <italic>laciniata</italic>, one of three varieties of <italic>L. exigua</italic>, a winter-annual plant endemic to the central United States. Because <italic>L. exigua</italic> var. <italic>laciniata</italic> occupies a narrow geographic range and is experiencing major habitat loss, it was recently listed as threatened; however, little is known about its genetic diversity and implications for conservation. We conducted a range-wide population genetic study of <italic>L. exigua</italic> var. <italic>laciniata</italic> and <italic>L. exigua</italic> var. <italic>exigua</italic> to understand: (1) levels of genetic diversity within and among populations, (2) whether <italic>L. exigua</italic> var. <italic>laciniata</italic> is genetically distinct from <italic>L. exigua</italic> var. <italic>exigua</italic>, and (3) implications for conservation. <italic>L. exigua</italic> var. <italic>laciniata</italic> showed identical genotypes at all 16 microsatellite loci across most of its range, fixed heterozygosity at some loci, and significant heterozygote excesses, consistent with a lack of recombination associated with an asexual mating system, which has not been documented previously in <italic>Leavenworthia</italic>. Because <italic>L. exigua</italic> var. <italic>laciniata</italic> is an annual and the same genotype occurs across multiple populations, asexuality may be caused by apomixis, asexual reproduction via seed. In contrast, most populations of <italic>L. exigua</italic> var. <italic>exigua</italic> demonstrated population genetic patterns consistent with a self-compatible mating system. Because <italic>L. exigua</italic> var. <italic>laciniata</italic> is morphologically, geographically, and genetically distinct, it should be recognized as an evolutionarily significant unit for conservation. We recommend maintaining large population sizes to conserve evolutionary potential in <italic>L. exigua</italic> var. <italic>laciniata</italic>, as the likelihood that facultative sexual reproduction may occur may be greater in larger populations. Additional research in <italic>L. exigua</italic> var. <italic>laciniata</italic> is needed to confirm the occurrence of asexuality and apomixis, clarify its reproductive isolation from other taxa, and to understand whether it exhibits residual sexual reproduction, epigenetic variation, or phenotypic plasticity to help it persist in response to environmental variation. In the future, <italic>L. exigua</italic> var. <italic>laciniata</italic> may serve as an important model in which to investigate the conservation of threatened plant species with little genetic variation in a changing climate.</p>