Genetics study findings: Implications for saving America's last wild bison

For Immediate Release:
February 8, 2011

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Thomas H. Pringle

Montana - A new study called "Widespread Mitochondrial Disease in North American Bison" concludes inherited disease is common in national park bison.

Published in Nature Precedings on February 7, 2011 http://precedings.nature.com/documents/5645/version/1 the study by geneticist Thomas Pringle looked at small energy producing factories inside cells called mitochondria.

He reports that of the thirteen proteins made from bison mitochondrial DNA, eleven are normal but two are mutated.

Symptoms of the disease may include fatigue while running, lactic acid buildup in the blood and ragged red muscle fibers.

Bison may get tired while running, succumb to prolonged winter cold, get fatigued brushing snow aside for feeding, lose out in breeding competitions or fall to predators. The study looked only at bison DNA and did not assess mitochondrial function in a laboratory.

Mitochondrial disease is non-infectious and inherited strictly from mothers. The maternally acquired gene affects genetically pure bison in North America, and is unrelated to introduced brucellosis and nineteenth century bison-cattle hybrids.

Bulls do not pass on mitochondria and may provide valuable genetic diversity that keep the species fit.

Mitochondria are the energy producing engines in cells. Bison inhabiting harsh environments like Yellowstone National Park need healthy functioning mitochondria to survive freezing temperatures, migration through accumulating snow pack to access forage, and evading predators says Pringle.

Mitochondrial disease is common in humans with 1 in 5,000 live births affected and 1 in 200 a carrier. Bison appear affected at a similar level.

Pringle surmises that the alarming incidence of reduced genetic fitness reported is due to the severe bison bottleneck of the nineteenth century, followed by decades of inbreeding in small herds and suppression of natural selection. Mitochondrial disease in Shetland sheepdogs has a similar history.

The disease was very rare in the past according to DNA analyzed from 44 fossil bison. However, Pringle says these particular genetic mutations have gained a wide foothold today.

Bison from Grand Teton National Park are the most affected, with all 29 bison tested to date carrying both genetic mutations.

Yellowstone bison are also affected to different extents in distinct Yellowstone National Park herds.

With the National Park Service estimating 1,000 bison or more migrating through deep snows this winter from the Northern Range of Yellowstone National Park, a high proportion of bison with healthy genetics are likely to be slaughtered.

The Northern Range subpopulation or breeding group are some of the last remaining bison free of mitochondrial disease based on its geographical distribution.

The deleterious mitochondria appears more frequently among bison in the Centrial Interior herd.

To date, Pringle has tested 179 bison in Yellowstone National Park and Grand Teton National Park for mitochondrial disease.

With these new findings, bison genetics researchers are calling for better management of national park herds to conserve the wild genome.
Pringle says "The bison crisis of the nineteenth century is not over by any means. We've recovered bison numbers okay but not their genetic fitness. Park visitors are being cheated. If we continue to slaughter the last bison with good genetics we'll soon reach the turning point at which bison recovery becomes impossible."

Bison aren't the only animal affected by inbreeding. The pygmy rabbit captive breeding program recently collapsed as did wild populations of Florida panthers. Government programs for condor and Mexican wolf recovery from population bottlenecks worse than bison have raised concerns among geneticists. Overall, the Endangered Species Act may be too little, too late. The law needs to kick in far earlier to save wild species say bison researchers.

Additional material on bison mitochondrial genomics can be found online: http://genomewiki.ucsc.edu/index.ph/Bison:_mitochondrial_genomics