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The first reproductive signs of inbreeding have been found in mountain lions being monitored in the Santa Monica and Santa Ana mountains, scientists say, a discovery that reveals a serious threat to the future survival of both populations.

Some of the big cats were recently found to have, on average, a 93% abnormal sperm rate — the first evidence that inbreeding is having an effect on the reproductive system, according to a UCLA-led study. That could eventually make it more difficult for the pumas to reproduce as the local population faces a lack of genetic diversity, representing a potential extinction threat.

“This is a serious problem for an animal that’s already endangered locally,” Audra Huffmeyer, a UCLA postdoctoral researcher who is the study’s lead author, said in a National Park Service news release. “It’s quite severe.”

Huffmeyer studies fertility in large cat species and is a National Geographic Explorer. 

Inbreeding has been known to be an issue for the mountain lion populations in the Santa Monica and Santa Ana mountains, with some of the big cats already showing some signs such as tail deformities and testicular defects, according to previous research.

The malformed sperm is the latest finding that reveals the extent of the trouble facing each group.

Both populations are hemmed in to their respective mountain ranges by busy freeways in the greater Los Angeles area, and Orange and Riverside counties, making it difficult for them to mate with cougars outside their own territories.

The National Park Service has been studying the inhabitants in the Santa Monica Mountains for about two decades, tagging and following more than 100 big cats to date.

The latest kittens to be incorporated in the study were a litter of four captured late last November, according to Park Service officials. They were apparently abandoned by their mother, who was not among the pumas being tracked.

Currently, more than a dozen mountain lions are being monitored with GPS collars in the Santa Monica Mountains National Recreation Area.

In the past year, researchers found nine adult males in both the Santa Monica and Santa Ana ranges that exhibited symptoms of inbreeding.

Sperm samples were also taken from five of the pumas after they died (from causes ranging from rat poison to being struck by a vehicle). Through the samples, the team discovered all five had high levels of abnormal sperm rate.

This first evidence of reduced infertility demonstrates the necessity for things like wildlife crossings over local freeways, so these animals could roam further in the urban sprawl and expand their pool of prospective mates, according to the release.

“If we don’t do anything to introduce more genetic diversity to the Southern California mountain lions, we will have more males with reproductive problems, fewer kittens and a lower rate of kitten survival,” Huffmeyer said in the release.

“If we don’t do anything to add genetic diversity, the end is near,” she added. “That sounds dramatic, but that’s what we’ve seen.”

A major issue is that few mountain lions have successfully made it across heavily-traveled freeways such as the 101 and 405, as well as other local roads. Vehicle crashes have been one of the leading causes of death to the puma population in the Santa Monica Mountains.

In some good news for the species, Caltrans is expected to break ground on a wildlife bridge this month above the 101 Freeway in the Agoura Hills area. And a possible crossing over the 15 Freeway in Riverside County is also in the early planning stages, NPS officials said.

But without sustained action, scientists predict the big cats could potentially face extinction in both Southern California mountain ranges this century.

“Although they haven’t seen evidence yet, once scientists start finding significant inbreeding depression — meaning decreased fertility and reduced kitten survival — extinction is predicted to occur within 50 years, with a median extinction time of 12 to 15 years,” the release stated, citing research papers from 2016 and 2019.

The study is scheduled for publication this month in the journal Theriogenology but can currently be found online here.