The mountain lions in Los Angeles’s Santa Monica mountains are so isolated from other cats – hemmed in by freeways and urban development – that biologists have long been worried they are at high risk of becoming inbred to the point of sterility. This week, researchers in California : three have L-shaped kinks at the end of their tails. What’s more, some of the males have cryptorchidism, a condition in which the testes fail to descend.
The local genetic diversity of mountain lions is the lowest of any lion population in the western US. A population in Florida in the eastern US – where the species is known as the Florida panther – had lower genetic diversity a few decades ago. Those cats also developed abnormalities.
“We’re seeing some of those exact same defects as Florida panthers,” says Seth Riley, the National Park Service (NPS) wildlife branch chief of the Santa Monica Mountains National Recreation Area, who led the study.
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Matings between offspring are common and some LA lions kill others to secure access to territory and mates. Just a handful have successfully navigated across the region’s highways over the last two decades, and many have died trying.
Holly Ernest at the University of Wyoming says that just  and that the abnormalities are “definitely concerning”.
“This is something we hoped to never see,” said Jeff Sikich, the NPS wildlife biologist who discovered the first kink-tailed mountain lion in March.
It is unclear whether tail variations effect sexual selection – for instance, if females will reject males with the kinked tails – but the species has displayed other odd features. In 2016, a young male in Idaho was , although this looks more like a chromosomal aberration than the result of inbreeding, says Kyle Gustafson at Arkansas State University.
In Florida, a mountain lion population in danger of becoming inbred was saved by the introduction of eight females from Texas. Shipping mountain lions to LA probably won’t work, however. An adult male’s range can extend more than 500 square kilometres, but the Santa Monica mountains encompass only about 700 square kilometres – and wildfires scorched half the area in 2018, “squeezing the animals even more”, says Riley, the NPS study lead.
A proposed bridge over a freeway could be a fix, but it would pricey, costing around $85 million. Despite public support, the bridge project has only raised around $15 million. Riley hopes that the project will break ground in late 2021.
“Folks are focused on other things with the state of the world, but plenty of people are interested in conservation,” he says. “If we increase connectivity and have animals moving back and forth, that’s a permanent solution, not just for mountain lions. Roads impact the genetics of everything from lizards to birds to bobcats. We’re the second largest metropolitan area in the country. Connectivity benefits all of us.”
