About Those “Pure” Catalina Bison…
Famous Herd Not Quite Purebred, According to USC and Texas A&M Biologists
The famous wild bison of Santa Catalina Island turn out to have some farm-raised ancestors.
The discovery came from a genetic analysis of 98 bison shipped to South Dakota’s Rosebud Indian Reservation in 2004. Almost half have cattle in their ancestry, according to a study in the current issue of Animal Genetics.
The authors, from the University of Southern California and Texas A&M, concluded that exporting Catalina bison to replenish wild herds “is ill-advised and should be avoided.”
The results of the study were not known at the time of the shipment to South Dakota, which was conceived for humanitarian purposes rather than genetic improvement.
More than 2,000 bison have been exported from Catalina since the herd was introduced in 1924, some for breeding and others for consumption.
The new genetic data contradict the conventional view that because they were isolated from cattle, Catalina bison are genetically purer than many herds on the mainland.
The animals’ genome does appear to be only 1 percent cattle, said corresponding author Dennis Hedgecock, professor of biological sciences at USC.
But in 45 percent of the animals, the mitochondrial DNA — a separate cluster of genes inherited only from the mother — comes from domestic cattle.
This implies that almost half the Catalina bison have a cow as a direct ancestor.
“I was shocked,” Hedgecock said. “You look at these animals, and there’s nothing cattle about them.”
Combining the DNA analysis with historical sources, the researchers traced the probable origin of the Catalina herd to the Goodnight Ranch in Texas, a place that co-author Suzanne Edmands called “ground zero” for interbreeding practices.
“The mixing came before they came to Catalina. We are quite certain,” said Edmands, associate professor of biological sciences at USC.
That information was not available in 2004, when the Catalina Island Conservancy mounted an effort to find a humane home for its surplus bison.
The conservancy is forced to reduce its herd periodically because the island cannot sustain more than a couple of hundred animals.
The conservancy settled on the Rosebud Sioux Tribe, which however lacked the money to move 98 bison across the country. Southern California’s Morongo Indians, operators of a thriving casino, agreed to absorb the cost.
Not all bison herds are mixed. An analysis of federal bison herds detected no cattle mitochondrial DNA in 10 herds and only 1.8 percent in the National Bison Range Herd.
However, Hedgecock suggested that the Catalina herd might have been “backcrossed” over time with pure bison, diluting the original contribution from cattle and explaining the small overall percentage of cattle genes.
Still, the authors wrote that their study “highlights new management concerns for the Catalina Island Conservancy,” which decides when and where to export bison.
Other authors of the study were USC graduate student Augustus Vogel and USC undergraduate Kimberly Tenggardjaja, who began the study during a USC course on conservation biology; and Natalie Halbert and James Derr from the Department of Veterinary Pathobiology at Texas A&M, who provided expertise on bison breeding.
USC’s Wrigley Institute for Environmental Studies supported the research.
Contact: Carl Marziali at (213) 219-6347 or marziali@usc.edu
