World / Science & Health

Highways fragment Southern California mountain lion gene pool


Mountain lions in Southern California are under growing pressure from a shrinking gene pool, fragmented by highways and urban sprawl that has left the cats’ territories increasingly isolated from each other, a study published on Wednesday showed.

Analysis of DNA from about 350 mountain lions, or cougars, statewide revealed that those in the Santa Ana Mountains southeast of Los Angeles are only about half as genetically diverse as more robust populations in the Rockies.

The Santa Ana range is surrounded by an expanding population of about 20 million people. A corridor linking cougar territory there to a bigger range — and more lions — to the east is cut off by a 10-lane highway.

The highway and development around it prevents cougars from freely roaming between the ranges, restricting gene pool replenishment, University of California at Davis scientists said in a study published in the journal PLOS ONE.

The highway also poses a road-kill threat to lions, and DNA samples show the region’s “genetic bottleneck” dates back about 80 years, coinciding with a period of tremendous human sprawl.

“That tells us it’s not just natural factors causing this loss of genetic diversity. It’s us, people, impacting these environments,” said Holly Ernest, a veterinarian and geneticist who co-authored the study.

Low genetic diversity, as demonstrated by the endangered Florida panther in the Everglades, leaves a population susceptible to hereditary abnormalities, such as heart defects and infertility.

It also makes the population less resilient to environmental changes like drought and habitat loss.

Combined with other factors — like poaching, disease or removal of cats deemed a public safety threat — a declining gene pool ultimately leads to “an extinction vortex,” Ernest said.

The Florida panther presents a worst-case scenario that has seen millions of dollars spent trying to bring it back from the brink of extinction since the 1990s, said Winston Vickers, a UC Davis-based veterinarian and researcher who was primarily responsible for catching lions for study.

“If we keep building without attention to these issues, we’re going to keep creating more pockets of isolation,” he said.

Recovery measures might include construction of wildlife passages beneath highways, fencing to prevent road kill, and importing cougars from elsewhere to inject fresh DNA into genetically stranded populations, he said.

The Santa Ana population is believed to be among the most vulnerable in California, where some 4,000 to 6,000 cougars are estimated to roam statewide.

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