| Geographical isolation is thought to permit divergence among populations by disrupting gene flow. This study examined the long-term effects of fragmentation on variable sized, insular populations of white pine (Pinus strobus ). The four study sites were connected to mainland Michigan roughly 10,000 y.b.p. and have been isolated from the mainland and each other since approximately 6,000 y.b.p. Results determined that white pine harbors high amounts of genetic diversity within populations, and little diversity among fragmented populations. This study found slight divergence with allozymes. The confidence interval for Fst among islands was 0.00 to 0.03 and among sample plots was 0.01 to 0.07. Diversity measures based on microsatellite markers also indicated some divergence. The Rst value among islands was 0.01, and 0.03 among sample plots. Estimates of inbreeding within islands were significantly different from zero. The confidence interval for Fis among islands ranged from 0.02 to 0.12, but was not significantly different from zero among sample plots. In addition, significant positive spatial autocorrelation was found in distance classes less than 5 km and 8.5 km among islands. Negative spatial autocorrelation was found at distances greater than 13.5 km among islands. Within the largest island, Beaver Island, significant positive spatial autocorrelation was found in distance classes less than 3.6 km, and a negative autocorrelation was found at distance classes greater than 13.5 km. These results suggest that the fragmentation and subsequent isolation has resulted in some divergence and inbreeding within islands, but that a limited amount of migration has prevented more severe divergence. |
