GENETIC POPULATION STRUCTURE ACROSS THE RANGE OF ENDANGERED NORTHEASTERN BULRUSH, SCIRPUS ANCISTROCHAETUS.

Premise of research. Determining population structure and the spatial distribution of existing genetic variation is important for prioritizing areas for conservation of endangered species. Specifically, identifying clusters of genetically differentiated populations ensures that the genetic diversity of a species is conserved. Scirpus ancistrochaetus, northeastern bulrush, is a federally endangered wetland sedge, found in eight states in the northeastern United States, for which little information on genetic structure is available. Methodology. We collected leaf samples from 96 separate wetlands spanning seven states and representing over half of all known sites (N p 71 sites). We sequenced eight variable loci, which were used to construct distance-based trees and calculate population-assignment probabilities to investigate population structure, and we tested isolation by distance by correlating genetic similarity with geographic distance among populations. Pivotal results. All plants sampled from the same wetland (i.e., a population) were genetically identical with low heterozygosity, and there was little to no variation among clustered wetlands within a site. Scirpus ancistrochaetus was genetically structured across its range. Notably, all populations from New England were genetically identical to each other but differed from all other populations, and a similar pattern was observed for northern Pennsylvania populations. Three genetic clusters were identified, including a primarily New England cluster, a primarily Pennsylvanian cluster, and a southern Appalachian cluster, and overall, genetic distances were consistent with isolation by distance. Although genetic clusters mostly corresponded with geography, some populations did not show this geographic-genetic association, suggesting long-distance dispersal; for example, one population from West Virginia was assigned to the New England cluster. Overall, the highest genetic diversity was found within Pennsylvania and nearby states. Conclusions. Whether similarity between geographically distant locations is due to animal-mediated gene flow or retention of ancestral alleles needs additional study. Additionally, the development of a large number of new markers may help to reveal diversity in areas such as New England with wetlands that did not have any diversity using our markers. Nevertheless, conservation of different genetic clusters at a regional scale is important for maintaining the genetic diversity of S. ancistrochaetus, particularly in its southern range, where the greater amount of genetic diversity suggests that this region is a reservoir of genetic variation. [ABSTRACT FROM AUTHOR]

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