Estimation of population reduction and gene flow in the rare orchid Isotria medeoloides

Isotria medeoloides (Pursh) Raf. is a threatened orchid species with an Appalachian distribution in the eastern United States. There are only 150 populations, 67 of which are in Maine and New Hampshire. The United States Fish and Wildlife Service is attempting to preserve the species by protecting populations and potential colonization sites. Previous microsatellite analysis of fifteen populations throughout the species revealed low genetic diversity and high inbreeding. This study uses four microsatellite loci to determine gene flow, effective population sizes, and population size reductions among eighteen populations in order to identify genetically important sites. Results indicate that populations in the southern range of the species are severely reduced. The relatively diverse northern populations also show signs of population decline. A coalescent genealogy sampler revealed low gene flow with most populations sending and receiving less than one migrant per generation. Gene flow was especially low among small southern populations.