Temporal changes in allele frequencies and low effective population size in greater prairie-chickens

The number of greater prairie-chickens in Wisconsin has decreased by 91% since 1932. The current population of approximately 1500 birds exists primarily in four isolated management areas. In previous studies of the Wisconsin populations we documented low levels of genetic variation at microsatellite loci and the mitochondrial DNA control region. Here we investigate changes in genetic structure between the four management areas in Wisconsin over the last 50 years. We estimated the harmonic mean effective population size (Ne) over the last 50 years by comparing allele frequencies from the early 1950s with those from contemporary samples. Using a pseudo-likelihood approach that accounted for migration, estimates of Ne (15-32 prairie-chickens within each management area) were 10 times lower than census numbers from booming-ground counts. These low estimates of Ne are consistent with increased habitat fragmentation and an increase in genetic isolation between management areas over the last 50 years. The reduction of gene flow between areas has reduced Ne, increased genetic drift and, consequently, reduced genetic variation. These results have immediate consequences for the conservation of the prairie-chicken, and highlight the importance of how mating systems and limited dispersal may exacerbate the loss of genetic variation in fragmented populations.