Assessing the status of sundial lupine ( <i>Lupinus perennis</i> L.) genetic diversity and population structure throughout its distribution

Habitat loss and fragmentation directly influence plant genetic diversity and how it is spatially structured. Species associated with shrinking habitats generally experience population declines and genetic erosion, potentially increasing extinction risk. An endangered North American habitat, the oak savanna, supports high plant biodiversity and is the primary habitat for sundial lupine (<i>Lupinus perennis</i> L.). This legume serves as the primary host plant for several highly specialized insects. Sundial lupine is declining in the eastern part of its range, and restoration efforts lack an understanding of the regional level of population differentiation in this species. In this study, we addressed this gap by characterizing the population genetic structure and levels of inbreeding of sundial lupine with nine microsatellite markers across 25 populations throughout its distribution. To assess whether losses of genetic diversity are impacting population fitness, we investigated whether germination rates were associated with within-population genetic diversity and inbreeding. Genetic diversity was greatest in the southernmost population (Florida). We found significant differentiation between populations (pairwise <i>G</i> _ST ranging from 0.003 to 0.63) and identified five genetic clusters with high levels of admixture. No sites showed significant levels of inbreeding (<i>F</i> _IS; mean -0.01, standard deviation 0.15). Germination success did not differ based on population size but decreased in populations with negative inbreeding coefficients. Our data suggest that there are significant levels of admixture between populations; thus, it is possible to use seeds from multiple sources for restoration. Still, due to the widespread distribution of sundial lupine, it is possible that populations may exhibit local adaptation to regional aspects of their habitat, and we caution against long-distance movement between populations.