Mountain lions living in the Santa Ana Mountains, a range that runs between Orange and Riverside Counties, have among the lowest genetic variability of all lions in the state, according to a UC Davis study published today in the journal PLOS ONE.
Their genetic restriction further highlights the challenges of keeping viable populations of mountain lions in Southern California.
“Coastal California is at high risk for losing mountain lion populations,” said Holly Ernest, who is the study’s lead author and who now works at the University of Wyoming.
The study, performed in partnership with the Nature Conservancy, sampled animals from 2001-2012 and is the largest performed on Southern California mountain lions, with analyses conducted on nearly 100 animals.
It found evidence that genetic diversity within the Santa Ana Mountains began to decline within the past 80 years, a timeframe that indicates urban development is a major factor.
“We did find that they have suffered a genetic bottleneck in recent decades, and that corresponds with recent urbanization and developments that humans caused,” Ernest said.
The mountain range is bounded to the north, west and south by heavy urbanized areas. A separate, genetically distinct population of cougars lives to the east, but the I-15 freeway effectively cuts off access to the fresh DNA pool it represents. Vehicle strikes are the leading cause of mortality in the Santa Ana population.
This map identifies puma captures in the Santa Ana Mountains and eastern Peninsular ranges of Southern California. The colors of symbols represent different genetic groups, illustrating barriers to gene flow. Busy highways and growing urbanization in the area threaten pumas and have led to their genetic decay, a UC Davis study found. (Credit: UC Davis / The Nature Conservancy)
Only one lion in 10 years is known to have crossed the I-15 from the eastern population into the Santa Ana Mountains. It successfully mated, bringing a fresh injection of DNA to the population. Ernest said that kind of trek is too infrequent an occurrence to depend on for continued viability.
“That happens really, too rarely for the Santa Anas. The mountain lions that try to cross I-15 are getting killed, when normally there would be much more genetic movement,” Ernest said.
The story of mountain lions imprisoned by busy freeways and urban development is mirrored further north in the Santa Monica Mountains. A recent study by National Park Service scientists showed that the 101-Freeway has caused a similar restriction to movement for those lions, resulting in multiple known instances of direct inbreeding.
Ernest, who also performed genetic analysis for that study, said it has not yet been determined if direct inbreeding has occurred in the Santa Ana Mountains population but that the lions there have a similar amount of genetic restriction.
“Of all the mountain lions I’ve studied over the last 20 years, those two populations — the Santa Monicas and the Santa Anas — have among the lowest genetic diversity, approaching that of Florida Panthers,” Ernest said.
The Florida Panther problem
The Florida Panther has been held up as an example of the potential ravages that genetic restriction can have in mountain lions. Severe inbreeding in that population led to health and reproductive problems that put the subspecies on the path to extinction.
The Florida Panther population was stabilized by the introduction of pumas from outside the state. While that program is considered to have been a success, such introductions are costly and controversial, because they can lead to manufactured and deadly conflicts.
A kinked tail was a physical trait commonly found among the inbred Florida Panthers. Scientists on the Santa Ana study noticed two of the lions they monitored had similarly kinked tails.
The causes of the tail kinks are unknown and may have been caused by physical damage; however, genetic analyses showed the two lions were among the lowest genetically diverse in the study.
“Those kinked tails may not be due to genetics, but there’s a correlation there that at least tells us we better keep an eye on this. We better keep an eye on what mountain lion health looks like in Southern California and keep an eye on their genetic diversity and then work to conserve their populations,” Ernest said.
As of yet, Ernest said no evidence exists yet that ties health impacts in the population to their genetic restriction. She and colleagues have received a grant from the National Science Foundation that will allow them to examine instances of disease within the population and perform more intricate analyses of their immune systems.
Ernest said that she believes the population can be sustained if habitat is conserved and transportation corridors are built or improved upon to enhance the lions’ ability to migrate.
She said doing so would save money and avoid having to take drastic measures in the future.
“It cost millions and millions of dollars to bring (Florida Panthers) back to health again,” Ernest said. “If we do some more simple actions now with coastal California mountain lions, society won’t have to spend as much money later.”