November 7, 2003
Some re-established elk herds lack genetic diversity of ancestors
WEST LAFAYETTE, Ind. Continued monitoring is central to maintaining genetic diversity, which is the key to long-term success of animal reintroduction programs, according to research at Purdue University.
A team of researchers found that elk relocated to depleted areas lost significant amounts of diversity when only a few individuals were introduced to a new area or herds were not managed appropriately. Their findings could aid in the design of future wildlife management programs.
"Any new reintroductions that are performed need to take into consideration that how you manage those animals after you relocate them is just as important as it is to put them there in the first place," said Gene Rhodes, Purdue wildlife geneticist.
"Despite the fact that elk have been moved all over the United States, no one has looked at the effects of those reintroductions. These studies add to a growing body of literature that deals with reintroductions in general, and the genetic results of reintroductions of large animals."
Elk once roamed across most of North America, but extensive hunting and habitat loss throughout the 1800s nearly wiped out the species from much of its range. In the late 1800s, wildlife managers began transporting elk from large, stable herds in western states to locations throughout Canada, Mexico and other parts of the United States with the goal of restoring elk to parts of its historic range.
Those reintroduction programs met with variable levels of success, and in one study, published in Molecular Ecology, Rhodes and his colleagues compared the genetics of a reintroduced herd in Pennsylvania with the genetics of its source herds in Wyoming and South Dakota. Pennsylvania elk were hunted to extinction by the late 1800s, and in the early 1900s, wildlife managers in Wyoming and Colorado began shipping elk by train to Pennsylvania where the animals were released in the hope of restoring the species.
In a second study to be published in the January Journal of Wildlife Management, the researchers assessed genetic variation in California's Tule elk. Tule elk were not reintroduced from out-of-state herds, but early in the 20th century the small number of individuals remaining in California were used to re-establish Tule elk within the state.
Both the Pennsylvania and Tule elk studies show a significant loss of genetic diversity can occur in the course of reintroduction programs and during the time after the animals are released.
In both of these studies, Rhodes and his colleagues used a genetic technique that has become a popular component of the wildlife biologist's toolkit: DNA microsatellite analysis. Microsatellites, which are often used in human genetic studies, are short, repetitive pieces of DNA that are passed down from parents to offspring.
Unlike genes, microsatellites typically do not code for any specific information. Instead, scientists consider them to be neutral markers that indicate an organism's overall genetic diversity. They also can be used to infer aspects of a population's history.
"We use microsatellites as a kind of flag, a marker for what a population has gone through in the past," Rhodes said.
Wildlife biologists today use microsatellites to study a host of population parameters, including animal migration patterns, parentage in animal populations, and, like Rhodes, the genetic history of groups of reintroduced animals.
The extremely limited microsatellite variation Rhodes and his colleagues found among elk in Pennsylvania and California confirms that both groups of elk have experienced what conservation biologists call a bottleneck.
During a bottleneck, the numbers in a population decrease to extremely low levels, and later return to higher levels as the population begins to recover. The individuals that survive the bottleneck represent a decrease in genetic diversity that is passed on as the population rebounds.
One consequence of the decrease in a population's genetic diversity is that it may become difficult for populations to adapt to changing conditions.
"Genetic variation is the buffer against environmental change," Rhodes said. "If you have very limited genetic diversity, you may not have the genetic potential to respond if the environment changes."
Reintroducing a population of animals may simulate a bottleneck effect, especially if the reintroduction is done with a small number of animals or if the animals used represent only a small subset of the original genetic diversity present in the source herd.
Herd management is the key to minimizing the losses in diversity that may accompany reintroduction programs, the researchers said.
"The best effort we can do is to bring in lots of animals when setting up a reintroduction," said Christen Lenney Williams, who worked on the study as a postdoctoral researcher and is now a wildlife geneticist with the National Wildlife Research Center in Colorado. "In certain situations, we may also improve diversity by bringing in animals from a variety of herds. In other cases, moving animals between reintroduced herds may also help."
Williams also pointed out the financial reality of putting together a successful reintroduction program.
"If the time and money it takes to release an animal are going to be well-spent, then money should also be set aside for some post-release monitoring of the herd," she said.
"That's probably one of the biggest problems in some of the release programs, not just in elk, but other species as well. Once the animals have been released, the post-release monitoring hasn't had as much funding as it probably needed."
Other researchers who collaborated on these studies were Rawland Cogan, senior development officer with the Rocky Mountain Elk Foundation; Barbara Lundrigan, assistant professor of zoology at Michigan State University; and Thomas L. Serfass, associate professor of biology at Frostburg State University in Maryland.
The Rocky Mountain Elk Foundation and the Smithsonian Institution provided funding for these studies.
Writer: Jennifer Cutraro, (765) 496-2050, firstname.lastname@example.org
Sources: Gene Rhodes, (765) 414-3211, email@example.com
Christen Lenney Williams, (970) 266-6142, christen.l.Williams@usda.gov
A publication-quality photograph is available at http://ftp.purdue.edu/pub/uns/rhodes.elk.jpeg
Analysis of microsatellite variation in Tule elk
and Olin E. Rhodes
California's 22 Tule elk (Cervus elaphus nannodes) herds reportedly were founded by the single elk pair remaining in southern California in the 1870s and have been extensively managed during the ensuing 132 years. In this first report of microsatellite variation among Tule elk herds, few significant genetic differences were detected among herds and variation at 12 microsatellite loci was extremely limited within Tule elk herds. There were large and significant differences between Tule elk and both Rocky Mountain (C. e. nelsoni) and Manitoban elk (C.e. manitobensis) at the same 12 microsatellite loci and Tule elk possessed 50 percent of the allelic diversity and heterozygosity found in the other subspecies. Tule elk were fixed at 5 loci at which the other subspecies possessed an average of 4.6 alleles. We observed very large pairwise Fst values and genetic distances between Tule elk and both other subspecies, likely due to the very restricted variation in Tule elk, rather than the presence of unique variation. Modeling of the genetic characteristics of the Tule elk indicated that management strategies involving transplants among all herds appear to be the most beneficial for the maintenance of nuclear variation in the subspecies. We also investigate impacts of small herd size and varying sex rations on maintenance of microsatellite variation in Tule elk.
Microsatellite variation in the reintroduced Pennsylvania elk herd
Relocation programs have restored elk (Cervus elaphus) to portions of its vast historical range. We examine the consequences of these relocation programs by assessing variation at 10 microsatellite loci in three elk herds, a source herd (Yellowstone National Park), a large herd reintroduced from Yellowstone (Custer State Park) and a bottlenecked herd reintroduced from both Custer and Yellowstone (the Pennsylvania herd). Observed single-locus heterozygosities ranged from 0.000 to 0.739. Multi-locus heterozygosities ranged from 0.222 to 0.589. Although significant differences were detected among all three herds, the Yellowstone National Park and Custer State Park herds possessed similar levels of variation and heterozygosity, and the genetic distance between these two herds was small. The Pennsylvania herd, on the other hand, experienced a 61.5 percent decrease in heterozygosity relative to its source herds, possessed no unique and few rare alleles, and the genetic distances between the Pennsylvania herd and its sources were large. Simulations were performed to identify bottleneck scenarios in agreement with levels of variation in the Pennsylvania herd. Our data confirm that the rate of population growth post-relocation may have important genetic consequences and indicate that theoretical predictions regarding the maintenance of genetic variation during relocation events must be viewed with caution when small numbers of a polygynous species are released.