Genetic outcomes of translocating bighorn sheep

Date:
June 3, 2020
Source:
University of Wyoming
Summary:
Bighorn sheep have maintained a distinctive population genetic
structure in Wyoming, even with historical population losses and
translocations.



FULL STORY ========================================================================== Translocation is an important management tool used for nearly 100
years to increase bighorn sheep population numbers in Wyoming and to
restore herds to suitable habitat throughout their historical range. Yet, translocation also can alter the underlying genetic diversity of managed wildlife species in both beneficial and detrimental ways.


==========================================================================
To evaluate the long-term impact of bighorn sheep translocations, a
University of Wyoming professor and postdoctoral researcher co-led a
study from 2015-19.

The research group characterized statewide genetic structure and diversity
by using microsatellite and mitochondrial DNA data in 353 indigenous
and translocated Rocky Mountain bighorn sheep populations in Wyoming.

"The results of this study provide a comprehensive view of the level of
genetic diversity in bighorn sheep in Wyoming. This is really important
because bighorn sheep populations in Wyoming and throughout the West
were driven down to such low numbers between the gold rush era and
the 1960s," says Holly Ernest, a UW professor of wildlife genomics and
disease ecology, and the Wyoming Excellence Chair in Disease Ecology in
the Department of Veterinary Sciences and the Program in Ecology. "This
loss of population numbers historically was due, in large part, to
part overharvest, exposure to livestock diseases and loss of their
habitat. In Wyoming, they perhaps existed in the hundreds of thousands pre-mid-1800s, but were driven down to as low as 2,000 total in Wyoming
by the 1960s. Large losses of individuals often mean large loss of
genetic diversity, which is a major foundation of healthy populations."
Ernest was the senior and corresponding author of a paper, titled
"Bighorn Sheep Genetic Structure in Wyoming Reflects Geography and
Management," that was published in the May 29 online edition of the
Journal of Wildlife Management.

The journal publishes manuscripts containing information from original
research that contributes to basic wildlife science. Suitable topics
include investigations into the biology and ecology of wildlife and
their habitats that have direct or indirect implications for wildlife management and conservation.

Sierra Love Stowell, a research genomicist and a UW postdoctoral
researcher at the time (2016-18) of this work, was the paper's lead
author. Roderick Gagne, a research scientist at Colorado State University
and a UW postdoctoral researcher from 2015-17, and Doug McWhirter, a
Wyoming Game and Fish Department wildlife biologist, were co-authors of
the paper. Additionally, other wildlife biologists and officials from
the Wyoming Game and Fish Department contributed to the paper.

Bighorn sheep are a key component of Wyoming's biodiversity and a species
that provides important viewing and hunting opportunities.



========================================================================== Translocation is a tool used in wildlife management that involves the intentional, human-mediated movement of individual animals, populations
or species from one area with release in another. Beyond the demographic effects of adding more individual bighorn sheep, translocated animals
bring more genetic material that can increase genetic diversity and
improve fitness in recipient populations. Translocation of bighorn sheep
in Wyoming began in 1922 and still occurs today.

The study found there was high gene flow -- genetic interchange due to
movement of animals with resulting successful breeding -- among herds that
had translocation sources in common, and herds that received translocated individuals from other herds.

"We identified at least five genetic clusters of Rocky Mountain bighorn
sheep in the major mountain ranges of Wyoming," Ernest says. "These
genetic clusters generally align with current management units." The herd units identified were in the Absaroka, Devil's Canyon, Jackson, Kouba
Canyon and Whiskey Mountain areas.

For example, there is high gene flow among Devil's Canyon, Laramie Peak
and Ferris-Seminoe herds. Devil's Canyon, including the surrounding
habitat in the Bighorn Mountains, received the most translocations of
any herd in Wyoming, including translocation of bighorn sheep from
Whiskey Mountain near Dubois; Morgan Creek, Idaho; Missouri Breaks,
Mont.; and the Lower Deschutes River, Ore.



========================================================================== Laramie Peak also received translocations from Whiskey Mountain and
Montana.

The Ferris-Seminoe herd was founded by translocation and continues to
receive individuals from Devil's Canyon.

Ernest says the most interesting finding of the study is that bighorn
sheep have maintained a distinctive population genetic structure in
Wyoming, even with historical population losses and translocations.

"We found this intriguing and important, because we might have expected
that the very large reductions in population sizes and extensive
translocation events might have caused disintegration of population
genetic structure, and an appearance of Wyoming bighorn sheep to be
panmictic or 'all interbreeding,'" Ernest says. "But, they are not. They
have distinctive populations." The study used a panel of 38 variable microsatellite loci and 512 base pairs of mitochondrial DNA sequence to identify the genetic structure throughout the state and in translocation
source herds; quantify the extent of genetic diversity within each
genetic cluster; and estimate the degree of gene flow among herds.

In the early 1800s, the estimated number of bighorn sheep in Wyoming was between 150,000 and 200,000. Overharvest, habitat loss and livestock- transmitted disease outbreaks led to severe population declines. By
the 1960s, bighorn sheep numbers had dwindled to about 2,000 before
rebounding to roughly 7,000 in 1990.

Today's estimates are between 6,000 and 7,000 animals, with variable demographic rates between herds. Population rebound following the steep
decline is attributed to management efforts, which include limiting
harvest, preventing disease outbreaks and translocating individual sheep
for reintroduction and demographic control.

The study's results provide a statewide assessment of genetic diversity
and structure that will enhance management by understanding the outcomes
of translocation, identifying the source of unknown individuals and parameterizing disease ecology models, Ernest says.

"The source herd identification of wandering bighorn sheep is important
when determining if management actions, such as herd reductions, can
be applied to reduce the likelihood of animals leaving the herd for
extended forays," Love Stowell says. "Effective population sizes are
low in most Wyoming herds, suggesting that managers should weigh the
importance of maintaining gene flow for increasing genetic diversity
and effective population size against the risks of disease transmission, outbreeding depression, phenology mismatch and other factors. Finally,
this research provides a baseline for genetic monitoring in the face
of future disease outbreaks or extreme weather events." Outbreeding
depression is described as interbreeding between two distinct populations
that can lead to reduction in service and reproduction, Love Stowell
says. Phenology mismatch is the timing of life events, such as lambing
of bighorn sheep and their environment.


========================================================================== Story Source: Materials provided by University_of_Wyoming. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Sierra M. Love Stowell, Roderick B. Gagne, Doug McWhirter, William
Edwards, Holly B. Ernest. Bighorn Sheep Genetic Structure in
Wyoming Reflects Geography and Management. The Journal of Wildlife
Management, 2020; DOI: 10.1002/jwmg.21882 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200603144329.htm https://www.sciencedaily.com/releases/2020/06/200603144329.htm

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