Population Genomics and Conservation of Erigenia bulbosa (Apiaceae), an Edge-of-Range Species in Pennsylvania

Abstract

Premise of research. Erigenia bulbosa, or the harbinger of spring, is one of the earliest-blooming wildflowers in eastern North America. As a spring ephemeral of forests and woodlands, it is a common species throughout the Midwest. In Pennsylvania, E. bulbosa exhibits an east-west disjunct distribution, where widespread western populations are contiguous with the midwestern range and a handful of smaller populations in the eastern part of the state are restricted to the lower Susquehanna River Valley. The relative isolation of the eastern populations suggests a possible conservation concern; the smaller, less connected populations may be threatened by fluctuations in size and the potential for low genetic diversity. As a consequence, establishing regulatory measures in Pennsylvania has been problematic because of disagreement regarding how to treat E. bulbosa during the Pennsylvania Department of Conservation and Natural Resources (PA DCNR) environmental review process. Currently, populations in the east are subject to regulation, while populations in the west are not.Methodology. To better understand the population genetics of the species, we coupled field assessments of E. bulbosa with a population genomics approach. We sampled multiple individuals from eight populations and generated a genotyping-by-sequencing data set of single-nucleotide polymorphisms (SNPs) that we used to calculate population statistics (genetic variation [FST], inbreeding coefficient [FIS], and heterozygosity), estimate population structure (sparse nonnegative matrix factorization), identify clusters of genetically related individuals (discriminant analysis of principal components), estimate a NeighborNet, look at signatures of isolation by distance (IBD), and detect population differentiation (analysis of molecular variance) using the filtered SNP data set.Pivotal results. Our data reveal structure in all populations and suggest genetic isolation between the groups of populations in the eastern and western portions of the state. Genetic groups identified using multivariate methods correspond to populations. Within populations, we estimate low levels of heterozygosity, a significant signature of IBD, and that most of the genetic variation we find is due to differences between populations.Conclusions. Our results indicate that any conservation measures undertaken by the PA DCNR should be applied evenly throughout Pennsylvania. We expect that most populations will continue to be threatened by land use and other development activities. This work illustrates the strength of academic and nonacademic partnerships in fostering outcomes that inform conservation activities for local species of concern.