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Lassen National Park's Red Foxes May Get Genetic 'Rescue' To Save The Species

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By

Justin Housman

Published Date

October 28, 2024

A red fox rests near Lassen Peak / CA Department of Fish and Wildlife

For decades, researchers have been concerned about the declining population of montane red foxes in the Sierra Nevada mountains. There are two distinct populations of sub-species, one in the central Sierra, and another in and around Lassen Volcanic National Park, in northern California. Biologists think there are fewer than 30 red foxes left in the Lassen area.

Trapping and poisoning were disastrous for the fox population in the 19th and early 20th centuries, but the numbers of foxes haven't recovered the way they would in a healthy, thriving environment. This has puzzled biologists for decades, but a study of the Lassen red foxes from the University of California, Davis, points to a particularly challenging threat to the animals' survival— inbreeding. But, crucially, it also points to a potential saving grace for the red foxes. Breeding them with foxes from outside the region, in what's called a genetic rescue. 

The fox population near Mt. Lassen is largely cut off from foxes elsewhere in Western states. This forces them to breed with only each other, resulting in a reduced gene pool, which magnifies and concentrates any genetic deficiencies in the population. Eventually this creates an inbreeding depression, and is a big reason for the red foxes' decline around Lassen. 

This was discovered by reading the genomes of the Lassen red foxes as a kind of genealogical history book. 

Cate Quinn, a U.S. Forest Service research biologist and a lead author of the study, explained that by recovering bits of genetic material from red fox hair and stool, researchers are able to look into the animals' genomic past to determine whether or not the population was always so isolated. What Quinn discovered was the montane red foxes around Lassen once were part of a much larger, genetically diverse grouping of red foxes ranging largely uninterrupted throughout the western states. "When we look at whole genomes of individuals we can use that data to peer back in time," said Quinn. "We can see that the genetic isolation of these red foxes is relatively recent."

Red fox pups at play / CA Department of Fish and Wildlife

This discovery both points to the cause of the red foxes' enduringly small population, and the potential for genetic rescue as a solution. 

A genetic rescue is a simple idea. Take an animal from a different population that is nonetheless related to the inbred group and allow them to breed. The introduction of new genetic material can begin to address the inbreeding depression over time. As multiple generations descend from the red foxes who first bred with the red foxes from outside the area, the genetic diversity expands and helps create a healthier, growing population. 

Genetic rescues aren't something to take lightly, as it's introducing entirely new traits into an animal population already under tremendous stress. But it has worked before. Most notably in the Florida panther, which nearly went extinct in the 1990s, until pumas from Texas were introduced to breed with their isolated feline counterparts in Florida. Though there have been some hiccups (the Texan puma DNA introduced some harmful mutations in the Florida cats), the population is more diverse, growing, and healthier than before the rescue. 

Quinn's research helped show that the genetic isolation of the Lassen red foxes is recent, so the variance in genomes between them and foxes elsewhere in the West isn't so large as to complicate the genetic rescue. But that's largely where Quinn's work ends. Though she was lead author of the paper that suggests genetic rescue can save the Lassen red foxes, it's up to land managers to carry out the operation and to select the population that will be used to breed with the Lassen red foxes. 

That of course is a complex decision. 

"The final decision has not been made of where the source population(s) will be coming from," said Chris Stermer, an environmental scientist with the California Department of Fish and Wildlife, who is involved in the research. "But currently the Rocky Mountain red fox population in the Wallowa mountains of northeastern Oregon is our top candidate."

To decide whether a population is fit to donate breeding animals, it must first be determined the genetic match makes sense, and that the donor population is robust enough to handle giving up some animals. That's the next phase of the Lassen red fox project—determining which population to choose from. 

As for how long it will take for any rescue effort to be considered successful, it will depend on a number of factors. 

"We hope to see signs of breeding by the newly released foxes in 1-3 years, and signs of increased reproduction, genetic variability, and an increasing distribution by 3-6 years," said Stermer. "This after around a 2-year fox trapping, transport, health screening, and release effort. However, the ultimate indicator of a successful recovery effort is when we begin finding evidence of restored connectivity and gene flow across the range of all [Sierra Nevada Red Fox] populations."

Stermer points out that before any attempt at breeding begins, it will take at least a few years to sort out the scientific details. Quinn's study is hugely important and illuminates a hopeful path forward for the red foxes, but now the ground work must be done. 

 

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