Abstract

Examining the genetic structure of sensitive species often provides insight for management decisions. Occasionally, examining the genetic structure of rare plants produces more questions than answers. The endemic herbaceous perennial Fritillaria eastwoodiae MacFarlane (Liliaceae) is a narrow endemic in the northern Sierra Nevada. The range of F. eastwoodiae overlaps three other Fritillaria species: F. micrantha, F. recurva, and F. affinis. Floral morphology in F. eastwoodiae is variable across the species range, with populations in the northern region resembling F. recurva and those in the south being more similar to F. micrantha, consistent with previous suggestions of a hybrid origin of the rare species. Given the geographic separation of the two regions of populations and the morphological differences among sites, an isozyme study was conducted to determine if the two regions of populations represent one or two taxonomic units. We examined a panel of 15 isozyme loci in a total of 24 Fritillaria populations: 14 F. eastwoodiae, two F. micrantha, five F. recurva, a single collection of F. affinis, plus two collections of intermediate morphology. The data revealed low levels of allelic variation in the collection (mean A=2.3, P=71%, Ho=0.22), and significant differentiation among all populations (FST=0.094, P<0.001) and between species (FRT=0.017, P<0.001). Within F. eastwoodiae, there was no evidence of differentiation between northern and southern regions (FRT=0.002, P=0.053). Further, we found no evidence of the genetic distinctiveness of F. eastwoodiae compared to the other three wider-ranging species. Principal coordinate analyses indicated F. micrantha and F. affinis to be highly similar, while both were distinct from F. recurva. Samples of F. eastwoodiae were either similar to one of the three alternate Fritillaria, or intermediate to the genetic groups. Admixture analyses identified two genetic clusters in the entire collection. The assignment of individuals to each cluster (or as putatively admixed) was consistent with F. eastwoodiae representing a hybrid swarm in this sympatric zone between Fritillaria species ranges. Additional morphological and genetic studies are underway to confirm this hybrid-origin hypothesis. Results may have far-reaching impacts on the taxonomic and protected status of F. eastwoodiae.