Population genetic analysis reveals a predominantly selfing mating system and strong genetic structuring in a naturally fragmented, threatened plant

Conservation genetics studies not only provide information about genetic diversity and genetic structure to inform conservation strategies, they can also help infer life history characteristics such as mating system, pollinator, and seed dispersal strategy of a plant species. Here, we investigated Geocarpon (Mononeuria minima; Caryophyllaceae), an extremely diminutive, poorly known plant species from the south-central U.S. that is threatened due to high habitat specificity and habitat loss. The goals of this study were to use genetic data to help understand the basic attributes of the biology of Geocarpon, including mating system and the spatial extent of gene flow, how genetic variation is partitioned within and among populations and across the landscape, and how to protect that genetic variation. Most Geocarpon populations are highly homozygous and genetically homogenous, indicating a predominantly selfing mating system. Although the species maintains some allelic diversity, the majority of genetic variation was partitioned among populations, even in groups separated by small geographic distances (≥ 0.5 km), indicating very localized seed dispersal (gravity or water). Because genetic variation is structured at a fine scale, to conserve the full range of genetic diversity it is necessary to protect a large proportion of the populations of the species; we recommend protection of as many currently unprotected sites as possible, particularly in areas of the geographic range where few populations are protected, combined with ex situ conservation seed banking in sites that cannot be protected. This study illustrates how life history characteristics, particularly mating system, strongly influence patterns of genetic structure and can have major effects on the strategy to conserve genetic variation in an endangered species.