The Western Prairie Fringed Orchid (Platanthera praeclara)is listed as a threatened species and is currently found in 6 States as well as Manitoba, Canada. The greatest threats to the WPFO are habitat loss or degradation through the conversion of tallgrass prairies to croplands, competition from invading plants, fire suppression, and overgrazing by range animals. Our study utilized microsatellite molecular markers to address three objectives 1. To determine the level of gene flow between populations; 2. To determine the level of inbreeding within populations; 3. To see if there is genetic structure and evidence of divergence among populations from Canada to Iowa.
Results/Conclusions
A significant Fst statistic comparing all populations (Fst = 0.108 DF = 239, p<0.001) indicated that there is significant structure among populations. Smaller more isolated populations had lower genetic diversity. The mean number of alleles per population was smallest for the Mower population (N = 12 plants). An AMOVA indicated that 11% of the variation in allele frequencies was among populations. The estimated number of migrants per generation was Nm = 2.065.
Population analysis of allele frequencies in six populations showed evidence of inbreeding in all populations. The fixation index showed a heterozygote deficiency in all populations (Fis = 0.247, P>0.001); the observed heterozygosites were lower than expected for all populations. We conclude that the populations we measured are experiencing significant inbreeding and isolation from one another despite a range of population sizes. These results suggest that the fragmented landscape of the upper Midwest is isolating populations that are separated from each other by 100’s of miles. This isolation may very well be causing increased selfing and inbreeding, which ultimately could lead to extinction vorteces, particularly in small isolated populations.