Genetic changes in reintroduced Rocky Mountain bighorn sheep populations

We compared allozyme variability in 4 reintroduced populations of bighorn sheep (Ovis canadensis) with their common source population in Wyoming to understand how reintroduction affects genetic variability. Founder size was low (8-69) and effective population size (N-e) remained low 10-20 years after release. Allele frequencies at 2 of 4 polymorphic loci differed between the reintroduced herds and the common source (P < 0.01), and the number of alleles per locus was reduced in reintroduced herds (P = 0.04). Multi-locus heterozygosity (at 29 loci) was lower (P = 0.03) in 3 of the reintroduced herds than in the common source population. Simulations of genetic drift in reintroduced herds indicated that allele frequencies were within expectations of model predictions, but that heterozygosity sometimes varied from predictions. Our results indicate the operation of founder effect and subsequent genetic drift within the small reintroduced herds, but also may be influenced by small sample sizes from herds that were difficult to sample. We suggest management practices that should minimize the loss of genetic variation from reintroduced populations of bighorn sheep.