Plains bison are an iconic symbol of America on everything from coins to
state flags. Now scientists writing in Conservation
Biology are exploring how the cross-breeding of bison with
domestic cattle in the late 1800s may still have unwanted effects on
modern populations of the species.
“The plains bison are an iconic symbol of rugged individualism and the
will to survive,” said Professor James Derr from Texas A&M University.
“The population crash and the spectacular recovery over the last 125
years is a classic example of the resilience of this species and the
success of science based wildlife conservation.”
Plains bison (Bison bison bison) once numbered in the tens of millions,
but they were driven to the brink of extinction in the late 1880’s
during America’s westward expansion. A small population of wild bison
survived in Yellowstone National Park, while 5 herds remained in the
hands of private ranchers. It is estimated that less than 100 surviving
bison became the common ancestors of today’s herds.
In some of these privately held herds, bison were crossed with
domesticated cattle in an attempt to introduce the hardy bison traits
into beef producing animals. While this effort failed to produce new and
improved beef breeds, some hybrids were created, and with the use of
molecular technologies, scientists have discovered a legacy of small
amounts of cattle genetic contamination in most bison herds in North
America.
“Looking at the long-term recovery of the bison it is important to find
out if this small amount of cattle genetics in an otherwise normal bison
can really have a biological effect,” said Derr. “We brought together
researchers from Arizona, California, Montana and Texas to find out.”
The team recorded size measurements for over 900 bison from a
nutritionally harsh environment for bison on Santa Catalina Island in
California and a nutritionally rich environment on a ranch in Montana.
The results revealed that bison with a particular domestic cattle
genetic trait, mitochondrial DNA, were consistently smaller and lighter
than animals with true bison mitochondrial DNA, in both environments.
“We have found that this cattle ancestry affects phenotypic traits and
most likely fitness of bison in herds which are maintained for both
production and species conservation,” concluded Derr. “Long term
management efforts with bison, and possibly other species with a history
of hybridization, must carefully consider the importance of genome
integrity in order to preserve what is the foundation and essence of
these species, their genomes.”
