The utilization of genetic markers to resolve modern management issues in historic bison populations: implications for species conservation

The saga of the American bison (Bison bison) is a well-known story of death, destruction, and greed circumvented by early conservationists. The foresight of 5 cattlemen and the Canadian and U.S. governments at the apex of the population bottleneck in the 1880s led to the eventual establishment of several federal bison populations, from which virtually all of the 300,000 extant bison are descended. A survey of 54 microsatellite loci spanning each autosomal and both sex chromosomes was used to compare levels of genetic variation among 10 of the 11 federal bison populations in the U.S. Although most populations contain moderate levels of genetic variation, the majority of genetic variation is contained within only 4 of the federal populations surveyed. The distribution and partitioning of genetic variation confirm historical records of founding lineages and transfers among populations. Previously published mitochondrial and nuclear markers were used to survey federal bison populations for evidence of domestic cattle introgression. While only 1 population was found to contain low levels of domestic cattle mitochondrial DNA, 7 of the 10 surveyed populations had detectable introgression of nuclear genes from domestic cattle. From this, 2 federal bison populations were identified that have both high levels of genetic variation and no evidence of introgression of domestic cattle genes.
The data obtained from this study were used to examine consequences of past and present management practices in closed bison populations. In the case of the Texas State Bison Herd, observed chronic small population size, low levels of genetic variation, low natality rates, and high juvenile mortality rates combined with the results of population modeling indicate a high risk of extinction within the next 50 years unless new genetic variation is introduced into the herd. Alternatively, analysis of population substructure and nonrandom culling reveal the necessity for further investigation into the long-term effects of current management practices in the Yellowstone National Park bison population. This study illustrates that while bison may be considered a conservation success story, long-term survival of protected federal populations requires the development of effective genetic management strategies.