Genetic Structure of Washington State Elk Herds
Kenneth I. Warheit, Senior Research Scientist

Washington State has ten elk herds that encompass the ranges of both the Roosevelt and Rocky Mountain subspecies. The management and viability of each of these herds depend, in part, on the degree to which individuals immigrate from one herd to another. For example, if there is no immigration between two herds, the herds are genetically isolated and changes in the numbers of individuals within each of these herds would be a function of their respective birth and death rates. However, if immigration occurs freely between these two herds they may behave as a single population and changes in the numbers of individuals within each of these herds would be a function of birth, death, and immigration rates. Because monitoring and affecting the number of individuals in wildlife populations such as elk herds is a responsibility of resource agencies, wildlife managers are keenly interested in understanding the geographic structure of populations and in quantifying immigration rates. Specifically in Washington State, one aspect of the geographic structure of elk herds is their subspecific composition; that is, the percentage of individuals that are of Rocky Mountain or Roosevelt descent.

There are two basic methods we can use to determine if individuals are moving among particular elk herds. The direct method involves marking individuals animals and surveying entire populations to determine the movement patterns of the marked animals. This method is logistically tenuous and extremely costly. A more cost-effective method is to indirectly quantify migration patterns by genetically characterizing each herd, first to determine the degree to which the herd is composed of Rocky Mountain versus Roosevelt individuals, and then to determine the amount of immigration or gene flow among the herds. The Washington Department of Fish and Wildlife (WDFW), in collaboration with the Rocky Mountain Elk Foundation, initiated a project in 2001 to study the genetic structure of Washington elk herds. With the assistance of some of the state’s elk hunters, volunteer organizations such as Eyes in the Woods, and tribal biologists, we obtained blood or muscle tissue samples from 345 elk representing nine herds within Washington, including elk from both Rocky Mountain and Roosevelt subspecies.

There are a variety of genetic techniques and molecular markers that can be used to investigate differences among populations of elk. For this project we used a molecular marker known as microsatellites. Microsatellites are pieces of DNA that do not produce proteins or any other product used by an organism, and mutate or change at a fairly high rate. To our knowledge, all animal species, including humans, have microsatellite DNA. An array of microsatellite markers can produce a genetic fingerprint that can be used to identify individual animals, or, with all individuals from a population taken collectively, can help determine if two or more populations (or herds of elk) are genetically “connected” through immigration. The degree to which populations (or herds) are genetically connected is a measure of how many individuals immigrate among these populations.

Our first goal in studying the genetic structure of Washington elk herds was to genetically characterize each of the state’s herds as being composed of either Rocky Mountain or Roosevelt individuals. Although we have collected sufficient data from only a few herds, preliminary results from our genetic analyses indicate that there are relatively large genetic distances between Rocky Mountain and Roosevelt elk, with all herds north and east of Mount Rainier (North Rainier, Colockum, Nooksack, Selkirk, and Yakima herds) composed mostly of Rocky Mountain elk, while the coastal herd (Olympic herd) is composed of Roosevelt elk. Two herds (St. Helens and Hanford herds) situated between these Rocky Mountain and Roosevelt herds are of mixed descent. Furthermore, these data also suggest that the elk herds in Washington are geographically structured, with some herds exchanging individual migrants, while other herds appear to be geographically and genetically isolated. However, more samples need to be collected from each of the herds and additional data need to be analyzed before these results can be confirmed.