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Island Fox - Urocyon littoralis
Island Fox - Urocyon littoralis

[Image: Island-fox-standing-in-grass_zps7a2ca092.jpg]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Urocyon
Species: Urocyon littoralis

The island fox (Urocyon littoralis) is a small fox that is native to six of the eight Channel Islands of California. There are six subspecies of the fox, each unique to the island it lives on, reflecting its evolutionary history. Other names for the island fox include coast fox, short-tailed fox, island gray fox, Channel Islands fox, Channel Islands gray fox, California Channel Island fox and insular gray fox.

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Taxonomy and evolution 
The island fox shares the Urocyon genus with the mainland gray fox, the species from which it is descended. Its small size is a result of insular dwarfism, a form of allopatric speciation. Because the island fox is geographically isolated, it has no immunity to parasites and diseases brought in from the mainland and is especially vulnerable to those the domestic dog may carry. In addition, predation by the golden eagle and human activities devastated fox numbers on several of the Channel Islands in the 1990s. Four island fox subspecies were federally protected as an endangered species in 2004, and efforts to rebuild fox populations and restore the ecosystems of the Channel Islands are being undertaken. Radio collars are being attached to foxes in an effort to track and locate the young foxes. To date these efforts have been largely successful.
There are six subspecies of the island fox, each of which is native to a specific Channel Island, and which evolved there independently of the others. The subspecies are:
  • Urocyon littoralis littoralis of San Miguel Island,

  • Urocyon littoralis santarosae of Santa Rosa Island,

  • Urocyon littoralis santacruzae of Santa Cruz Island,

  • Urocyon littoralis dickeyi of San Nicolas Island,

  • Urocyon littoralis catalinae of Santa Catalina and,

  • Urocyon littoralis clementae of San Clemente Island.

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Foxes from each island are capable of interbreeding, but have genetic and phenotypic distinctions that make them unique; for example, the subspecies have differing numbers of tail vertebrae.
The small size of the island fox is an adaptation to the limited resources available in the island environment. The foxes are believed to have "rafted" to the northern islands between 10,400 and 16,000 years ago. Initially, fox populations were located on the three northern islands, which were likely easier to access during the last ice age—when lowered sea levels united four of the northernmost islands into a single mega-island (Santa Rosae) and the distance between the islands and the mainland was reduced—it is likely that Native Americans brought the foxes to the southern islands of the archipelago, perhaps as pets or hunting dogs.
Based on the limited fossil record and genetic distance from its gray fox ancestors, the northern island fox subspecies are probably the older subspecies, while the San Clemente island fox has been only resident on its island for about 3,400–4,300 years, and the San Nicolas island fox established itself as an independent group about 2,200 years ago. The Santa Catalina island fox is potentially the most recently evolved subspecies, having been on its island for about 800–3,800 years. The fox did not persist on Anacapa Island because it has no reliable source of fresh water; Santa Barbara Island is too small to support the food demands of the fox.

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The island fox is significantly smaller than the gray fox and perhaps the smallest fox in North America, averaging slightly smaller than the swift and kit foxes. Typically the head-and-body length is 48–50 cm (18–20 in.), shoulder height 12–15 cm (4–6 in.), and the tail is 11–29 cm (4–11 in.) long, which is notably shorter than the 27–44 cm (10–17 in.) tail of the gray fox. This is due to the fact that the island fox generally has two fewer tail vertebrae than the gray fox. The island fox weighs between 1 and 2.8 kg (2.2 and 6.2 lb). The male is always larger than the female. The largest of the subspecies occurs on Santa Catalina Island and the smallest on Santa Cruz Island.
The island fox has gray fur on its head, a ruddy red coloring on its sides, white fur on its belly, throat and the lower half of its face, and a black stripe on the dorsal surface of its tail. In general the coat is darker and duller hued than that of the gray fox. The island fox molts once a year between August and November. Before the first molt pups are woolly and have a generally darker coat than adult foxes.

The island fox typically forms monogamous breeding pairs which are frequently seen together beginning in January and through the breeding season, from late February to early March. The gestation period is 50–63 days. The female island fox gives birth in a den, a typical litter having one to five pups, with an average of two or three. Pups are born in the spring and emerge from the den in early summer; the mother lactates for 7–9 weeks. Sexual maturity is reached at 10 months, and the females usually breed within the first year. Island foxes live for 4–6 years in the wild and for up to 8 years in captivity.

Ecology and behavior 
Its preferred habitat is complex layer vegetation with a high density of woody, perennially fruiting shrubs. The fox lives in all of the island biomes including temperate forest, temperate grassland and chaparral, with no island supporting more than 1,000 foxes. The island fox eats fruits, insects, birds, eggs, crabs, lizards, and small mammals, including deer mice. The fox tends to move around by itself, rather than in packs. It is generally nocturnal, albeit with peaks of activity at dawn and dusk. Activity also fluctuates with the season; it is more active during the day in summer than it is in winter.
The island fox is not intimidated by humans, although at first may show aggression. It is quite easy to tame and is generally docile. The island fox communicates using auditory, olfactory and visual signals. A dominant fox uses vocalizations, staring, and ear flattening to cause another fox to submit. Signs of dominance and submission are visual, such as facial expression and body posture. Its main vocalizations are barking and growling. The island fox marks territory with urine and feces.

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Conservation status 
A decline in island fox populations was identified in the 1990s. On San Miguel Island the decline began in 1994, the adult population falling from 450 to 15 in 1999. Similar population declines were discovered on Santa Cruz Island, where the population decreased from 2,000 adults in 1994 to less than 135 in 2000, and on Santa Rosa Island where foxes may have numbered more than 1,500 in 1994 but were reduced to 14 animals by 2000. Golden eagle predation, discovered when foxes were radio-collared and monitored, proved to be the cause of the high mortality rates.
Golden eagle predation is the primary cause of island fox mortality. The golden eagle was an uncommon visitor to the Channel Islands before the 1990s according to data gathered by Dr. Lyndal Laughrin of the University of California Santa Cruz Island Reserve, and the first golden eagle nest was recorded on Santa Cruz Island in 1999. Biologists propose that the eagle may have been attracted to the islands in the 1960s after the decline of the bald eagle. The golden eagle replaced the bald eagle and began to feed on feral pigs due to the decimation of the local bald eagle population due to DDT exposure in the 1950s—the bald eagle would have deterred the golden eagle from settling on the islands while it subsisted on fish.
The feral pigs on Santa Rosa were exterminated by the National Park Service in the early 1990s which removed one of the golden eagle's food sources. The golden eagle then began to prey on the island fox population. Feral pigs on Santa Cruz Island and introduced deer and elk on Santa Rosa Island were introduced almost seventy years prior to island fox decline, therefore, the golden eagle most likely did not seek these animals as alternative prey. This has occurred most likely as a result of a process known as 'apparent competition'. In this process, a predator, like the golden eagle, feeds on at least two prey, for example, the island fox and feral pigs. One prey item is adapted to high predation pressure and supports the predator population (i.e. pigs), whereas the other prey item (i.e. the island fox) is poorly adapted to predation and declines as a consequence of the predation pressure. It has also been proposed that complete removal of golden eagles may be the only action that could save three subspecies of the island fox from extinction. However, the pigs on Santa Cruz Island were killed by the Nature Conservancy under the idea that they brought the eagles to the foxes.
Introduced diseases or parasites can devastate island fox populations. Because the island fox is isolated, it has no immunity to parasites and diseases brought in from the mainland and are especially vulnerable to those the domestic dog may carry. A canine distemper outbreak in 1998 killed approximately 90% of Santa Catalina Island's fox population. After several years of carefully trapping the foxes and vaccinating them against distemper and rabies, their population has reached 1,542, surpassing the population of about 1,300 seen before the animals were ravaged by the disease that scientists believe was introduced by a pet dog or a raccoon from the mainland that hitched a ride on a boat or a barge.
Diminished food supply and general degradation of the habitat due to introduced mammal species, including feral cats, pigs, sheep, goats, and American bison, the latter having been introduced to Catalina Island in the 1920s by a Hollywood film crew shooting a Western, also has had a negative effect on fox populations.
The foxes threaten a population of the severely endangered loggerhead shrike in residence on San Clemente Island. The island fox population on San Clemente Island has been negatively affected by trapping and removal or euthanasia of foxes by the United States Navy. Since 2000, the Navy has employed different management strategies: trapping and holding foxes during the shrike breeding season, the installation of an electric fence system around shrike habitats, and the use of shock collar systems. With the gradual recovery of the shrike population on San Clemente Island, the Navy no longer controls the foxes. Automobile fatalities have also been high on San Clemente, San Nicolas, and Santa Catalina Islands.

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California's 'Dwarf' Fox Is Back From the Brink
Fox has one of the fastest recoveries in the Endangered Species Act's history.

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A Channel Islands 'dwarf' fox on Santa Cruz Island.

Ker Than in Santa Cruz Island, California
for National Geographic
Published May 28, 2013

Kneeling in the dirt beneath a sycamore tree, Christie Boser cradled the endangered island fox in her lap, firmly gripping its neck with a gloved hand while using the other to slip on a green blindfold that would keep the animal calm.

It had been captured the night before, lured into a metal cage by the scent of cat food and the promise of an easy meal. After weighing the creature, Boser ran a flea comb through its reddish-gray fur, massaged and petted its lean body, and probed its mouth to gauge its condition.

"All his claws look nice and pretty ... but he has a broken canine," said Boser, a scientist with the Nature Conservancy and the restoration manager on Santa Cruz Island, the largest in the chain of eight Channel Islands off the coast of California.

After a brief exam, Boser released the yearling fox, which scampered off and vanished into some nearby shrubs.

It wasn't too long ago that such a routine checkup was a lot less commonplace. One of America's rarest mammals, found only on six Channel Islands, the island fox was driven nearly to extinction in the 1990s by predatory golden eagles. By 1999, there were only about 85 island foxes left on Santa Cruz Island, while nearby San Miguel and Santa Rosa Islands were each down to about 15.

Today, the species is on the verge of a dramatic recovery—one of the fastest in the history of the Endangered Species Act—with nearly 2,500 on the Channel Islands.

"They were listed as endangered in 2004, and they're pretty much ready to come off that list at this point," said Timothy Coonan, a biologist with the U.S. National Park Service (NPS), which works with the Nature Conservancy to preserve resources on Santa Cruz Island.

Threat from the Skies

Scientists think the island fox is descended from mainland gray foxes that arrived on the Channel Islands sometime between 6,000 and 10,000 years ago, and that the animal's body shrank in size because of limited space and resources.

"It's probably the best known example of island dwarfism," Coonan said.

On the islands, the smaller foxes quickly differentiated into six new subspecies. Free from predators, they thrived until until the 1990s, when golden eagles arrived.

Historically, golden eagles never bred on the Channel Islands, but some do occasionally make the 25-mile (40-kilometer) trek from the California mainland.

In previous times, golden eagles arriving on the Channel Islands would have likely been chased off by bald eagles, which are intensely territorial. But the Channel Islands' bald eagles had been decimated decades earlier by the insecticide DDT, Coonan explained. From the 1940s to about the 1970s, chemical companies discharged millions of pounds of DDT into the ocean, where it contaminated the bald eagle's marine food supply.

In the '90s, golden eagles were drawn to Santa Cruz Island by its burgeoning feral pig population. The descendents of domestic farm animals brought to the island in the 1850s, the pigs provided a steady food source for the raptors.

"What the golden eagles were really depending on were the pigs. The foxes were kind of an ancillary snack," said Kate Faulkner, chief of natural resources management for Channel Islands National Park.

The loss of bald eagles, the arrival of golden eagles, and the island's thriving feral pig population created "a perfect storm of events" that nearly doomed the island foxes, Coonan said.

Sleepy Juice and Robo-Dogs

The crisis spurred a recovery effort by the NPS and the Nature Conservancy, which owns 76 percent of Santa Cruz Island. "We went to the wall on the island foxes," Coonan said. "In the park services, we're mandated to save everything entrusted to our stewardship. If we let the island foxes go extinct, we might as well not be here managing anything."

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Flowers on Santa Cruz Island, home of California's 'dwarf' fox.

Captive-breeding programs were established on Santa Cruz, Santa Rosa, and San Miguel islands. Contract hunters were brought in to remove the non-native feral pigs and sheep, which had stripped the islands of vegetative cover for the foxes.

And bald eagles—which feed mainly on fish and don't affect the foxes—were slowly reestablished on the islands while golden eagles were captured and released back on the mainland.

That last task proved especially challenging. "The last golden eagle pair was really tricky to get because they had seen all their buddies get captured," said the Nature Conservancy's Boser.

After increasingly creative attempts to catch the birds—including using a fake egg filled with a sedative that Boser called "sleepy juice," and a robotic dog dressed up to look like a fox, the final golden eagle pair was netted by helicopters in 2006. In total, 44 golden eagles were removed from the islands.

The night the last golden eagles were captured, Boser and her colleagues celebrated atop a mountain on Santa Cruz Island. "A collective cheer echoed across the Santa Barbara Channel," Boser said.

Swift Recovery

With the feral pigs and the golden eagles gone, the fox population rebounded—and with a swiftness that stunned even the scientists and conservationists involved.

Today there are about 1,300 foxes on Santa Cruz Island, 500 on San Miguel Island, and 600 on Santa Rosa Island, with each population having a 90 percent annual survival rate.

"It's a strange thing," Coonan said. "The official recovery plan has not even been finalized [by the U.S. Fish and Wildlife Service], and yet these populations are doing so well that they can come off the Endangered Species List."

Brian Hudgens, a research ecologist at the Institute for Wildlife Studies, which ran the fox captive-breeding program, agreed that some of island fox subspecies are just about ready for delisting.

"For the subspecies on San Miguel and Santa Cruz, their populations are large enough and they are doing well enough that they are no longer in danger," Hudgens said. "Santa Rosa is almost there. It'll probably take a couple more years."

The work to save the island fox is far from over, however. The Nature Conservancy and the NPS continue to monitor the foxes, keeping an eye out for dangers like pathogens and parasites, as well as looming threats such as climate change.

Another potential concern is genetic health. Despite rebounding to their predecline numbers, the species was so severely culled that the amount of variation in its gene pool might have been compromised.

Such a "population bottleneck" could impact the fox's ability to deal with disease or environmental change, said Gary Roemer, a biologist at New Mexico State University who has studied the island foxes.

One controversial solution would be to interbreed different subspecies of island foxes, Roemer said. A similar strategy was recently used to bolster the genetic health of Florida panthers, drawing on DNA from cougars from Texas.

Coonan said he is happy to shift from worrying about the fate of the foxes to monitoring their health.

"It's actually a great stage to be here in the island recovery," he said. "I can sleep a little bit more at night because of everything that's gone on." 
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Endangered foxes on Catalina Island get promising treatment to reduce ear tumors

Date: December 7, 2015
Source: University of California - Davis
Roughly half of Santa Catalina Island foxes were found to have ear canal tumors, but an ear mite treatment appears to be greatly helping the problem, according to two new studies.

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A male fox is in Banning Meadow on Santa Catalina Island. A team of scientists led by UC Davis found alarming rates of ear mites and ear canal tumors in the endangered foxes. Ear mite treatments they initiated have since dramatically reduced the problem, their studies show.
Credit: Julie Lynn King/Catalina Island Conservancy

Until recently, endangered foxes on California's Catalina Island were suffering from one of the highest prevalences of tumors ever documented in a wildlife population, UC Davis scientists have found. But treatment of ear mites appears to be helping the wild animals recover.

Roughly half of adult foxes examined between 2001 and 2008 had tumors in their ears, with about two-thirds of those malignant, according to a UC Davis study published this month in the journal PLOS ONE.

More than 98 percent of the foxes were also infected with ear mites. These mites appear to be a predisposing factor for ear tumors in the Santa Catalina Island fox.

Luckily for the foxes, the story doesn't stop there.

"We established a high prevalence of both tumors and ear mites, and hypothesized that there was something we could potentially do about it, which now appears to be significantly helping this population," said Winston Vickers, lead author of the prevalence study and an associate veterinarian with the UC Davis Wildlife Health Center at the UC Davis School of Veterinary Medicine.

Working closely with researchers from the Institute for Wildlife Studies and Catalina Island Conservancy, the scientists conducted one of the few studies to estimate disease prevalence in an entire free-living wildlife population.

Rare success story

A complementary study, also led by UC Davis and published in PLOS ONE today, found that treatments with acaracide, a chemical agent used to kill ear mites in dogs and cats, reduced the prevalence of ear mite infection dramatically, from 98 percent to 10 percent among treated foxes at the end of the six-month trial. Ear canal inflammation and other signs of developing ear tumors also dropped.

"It's rare to have a success story," said the ear mite study's lead author, Megan Moriarty, a student with the UC Davis School of Veterinary Medicine when the study began and currently a staff research associate at the UC Davis Wildlife Health Center. "It was interesting to see such striking results over a relatively short time period."

Santa Catalina Island foxes are intensively managed by the Catalina Island Conservancy. In 2009, when the mite treatment study began, the Conservancy added acaracide to the variety of preventative treatments they administer to the foxes each year.

The Conservancy confirms that, in the years since, the overall prevalence of ear mites has dramatically declined in the areas they normally catch and treat foxes, as have the rates of tissue masses in the ear canals, suggesting reduced tumor presence.

"The annual prophylactic acaracide treatment has greatly improved the overall condition of the foxes' ear canals," said Julie King, the Conservancy's director of Conservation and Wildlife Management and co-author of both studies. "Within just a few months post treatment, the presence of wax, infection, inflammation, and pigmentation virtually disappear. We have also noted an apparent reduction in the number of tumors observed, despite the fact that the absence of wax and other obstructions has made them easier to detect."

Conservancy biologists have also documented a cascade effect on the foxes' offspring, since most young foxes get the ear mites from their parents.

"Prior to treatment in 2009, approximately 90 percent of all pups handled had ear mites, whereas by 2015, mites were detected in only 15 percent of new pups." King said.


The studies pose new questions. For instance, the mite treatment certainly reduces the prevalence and severity of mite infection, as well as risk factors for tumor development, but what effect will it have on overall tumor and cancer rates for these foxes in the long term?

Also, ear mites infect other Channel Island foxes, but those foxes don't develop ear canal tumors. So why are Santa Catalina Island foxes predisposed to these tumors and not other Channel Island foxes? Vickers and colleagues are preparing to research possible genetic reasons for this.

"Catalina foxes have an over-exuberant tissue reaction to the same stimuli--the mites--and that appears to lead to the tumors," Vickers said. "That's why we gravitate toward genetics in addition to other factors."

The Santa Catalina Island fox is one of six subspecies native to the Channel Islands off the coast of Southern California. Its population declined dramatically in 1999 when a distemper epidemic decimated up to 90 percent of the population, prompting the federal endangered species listing for the roughly 150 foxes remaining. The population has since rebounded to an estimated 1,717 foxes.

Story Source: University of California - Davis. "Endangered foxes on Catalina Island get promising treatment to reduce ear tumors." ScienceDaily. (accessed December 8, 2015).

Journal References:
T. Winston Vickers, Deana L. Clifford, David K. Garcelon, Julie L. King, Calvin L. Duncan, Patricia M. Gaffney, Walter M. Boyce. Pathology and Epidemiology of Ceruminous Gland Tumors among Endangered Santa Catalina Island Foxes (Urocyon littoralis catalinae) in the Channel Islands, USA. PLOS ONE, 2015; 10 (11): e0143211 DOI: 10.1371/journal.pone.0143211

In this study, we examined the prevalence, pathology, and epidemiology of tumors in free-ranging island foxes occurring on three islands in the California Channel Islands, USA. We found a remarkably high prevalence of ceruminous gland tumors in endangered foxes (Urocyon littoralis catalinae) occurring on Santa Catalina Island (SCA)—48.9% of the dead foxes examined from 2001–2008 had tumors in their ears, and tumors were found in 52.2% of randomly-selected mature (≥ 4 years) foxes captured in 2007–2008, representing one of the highest prevalences of tumors ever documented in a wildlife population. In contrast, no tumors were detected in foxes from San Nicolas Island or San Clemente Island, although ear mites (Otodectes cynotis), a predisposing factor for ceruminous gland tumors in dogs and cats, were highly prevalent on all three islands. On SCA, otitis externa secondary to ear mite infection was highly correlated with ceruminous gland hyperplasia (CGH), and tumors were significantly associated with the severity of CGH, ceruminous gland dysplasia, and age group (older foxes). We propose a conceptual model for the formation of ceruminous gland tumors in foxes on SCA that is based on persistent, ubiquitous infection with ear mites, and an innate, over exuberant inflammatory and hyperplastic response of SCA foxes to these mites. Foxes on SCA are now opportunistically treated with acaricides in an attempt to reduce mite infections and the morbidity and mortality associated with this highly prevalent tumor.

Megan E. Moriarty, T. Winston Vickers , Deana L. Clifford, David K. Garcelon, Patricia M. Gaffney, Kenneth W. Lee, Julie L. King, Calvin L. Duncan, Walter M. Boyce. Ear Mite Removal in the Santa Catalina Island Fox (Urocyon littoralis catalinae): Controlling Risk Factors for Cancer Development. PLOS, December 7, 2015 DOI: 10.1371/journal.pone.0144271

Ear mites (Otodectes cynotis) and ear canal tumors are highly prevalent among federally endangered Island foxes (Urocyon littoralis catalinae) living on Santa Catalina Island off the coast of Southern California. Since studies began in the 1990s, nearly all foxes examined were found to be infected with ear mites, and ceruminous gland tumors (carcinomas and adenomas) were detected in approximately half of all foxes ≥ 4 years of age. We hypothesized that reduction of ear mite infection would reduce otitis externa and ceruminous gland hyperplasia, a risk factor for tumor development. In this study, we conducted a randomized field trial to assess the impact of acaricide treatment on ear mite prevalence and intensity of infection, otitis externa, ceruminous gland hyperplasia, and mite-specific IgG and IgE antibody levels. Treatment was highly effective at eliminating mites and reducing otitis externa and ceruminous gland hyperplasia, and mite-specific IgG antibody levels were significantly lower among uninfected foxes. Ceruminous gland hyperplasia increased in the chronically infected, untreated foxes during the six month study. Our results provide compelling evidence that acaricide treatment is an effective means of reducing ear mites, and that mite removal in turn reduces ear lesions and mite-specific IgG antibody levels in Santa Catalina Island foxes. This study has advanced our understanding of the underlying pathogenesis which results in ceruminous gland tumors, and has helped inform management decisions that impact species conservation. 
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Island foxes may need genetic rescue

Date: March 21, 2016
Source: Colorado State University

The island fox has made a remarkable comeback from the brink of extinction, with three of six populations on their way to becoming the fastest mammal recovered under the Endangered Species Act. But new research published online March 17 in Molecular Ecology uncovers a hidden danger to the future viability of some island fox populations.

Chris Funk, associate professor in the College of Natural Sciences' Department of Biology, led the research team that conducted the largest and most in-depth genetic study to date of California Channel Island foxes. Funk is also director of the SoGES (School of Global Environmental Sustainability) Global Biodiversity Center at CSU. The study confirmed that each island's fox population likely warrants designation as a unique subspecies. But it also found that one subspecies, on San Nicolas Island, may require genetic rescue to reduce its risk of extinction.

The San Nicolas Island fox has the lowest genetic variation ever found in a mammal species, making them especially vulnerable. "Low genetic diversity may lead to lower survival and reproductive success, and may reduce the ability of a population to adapt to climate change or new, introduced diseases," Funk said. "With a dwindling population of fewer than 300 adults, actions need to be taken quickly to preserve this important member of the Channel Islands ecosystem."

The scientists say that if this subspecies' genetic health is poor, it may be necessary to use "genetic rescue," bringing island fox individuals from other islands to boost the San Nicolas gene pool. This approach has been successfully implemented in the past to save populations from extinction, including the resuscitation of the Florida panther back in 1995.

The island fox is the smallest fox species in the U.S and found on six of the eight California Channel Islands. Four of the six fox subspecies (not including the San Nicolas population) were listed as endangered under the U.S. Endangered Species Act in 2004 due to precipitous population declines caused by predation by golden eagles and an epidemic of canine distemper virus. Since then, concerted efforts by various island managers enabled island fox numbers to recover sufficiently that the U.S. Fish & Wildlife Service plans to remove or move them down the list.

"The recent island fox recovery was the result of an impressive collaboration of scientists and land managers. It may now be time to examine whether unconventional methods like genetic rescue are needed for the San Nicolas Island fox," said Scott Morrison, The Nature Conservancy's director of science and a coauthor of the study.

If managers decide that genetic rescue is necessary to maintain robust populations of island foxes, this study can be used to inform which island fox subspecies would be the best source population.

Robert Lovich, a U.S. Navy biologist in California and a coauthor of the study, said: "Long-term monitoring of the island fox and new genomic technologies now give us the capacity for proactive management with far greater precision and a better expected outcome for island foxes in general."

Story Source: Colorado State University. "Island foxes may need genetic rescue." ScienceDaily. (accessed March 22, 2016).

Journal Reference:
W. Chris Funk, Robert E. Lovich, Paul A. Hohenlohe, Courtney A. Hofman, Scott A. Morrison, T. Scott Sillett, Cameron K. Ghalambor, Jesus E. Maldonado, Torben C. Rick, Mitch D. Day, Nicholas R. Polato, Sarah W. Fitzpatrick, Timothy J. Coonan, Kevin R. Crooks, Adam Dillon, David K. Garcelon, Julie L. King, Christina L. Boser, Nicholas Gould, William F. Andelt. Adaptive divergence despite strong genetic drift: genomic analysis of the evolutionary mechanisms causing genetic differentiation in the island fox (Urocyon littoralis).Molecular Ecology, 2016; DOI: 10.1111/mec.13605

The evolutionary mechanisms generating the tremendous biodiversity of islands have long fascinated evolutionary biologists. Genetic drift and divergent selection are predicted to be strong on islands and both could drive population divergence and speciation. Alternatively, strong genetic drift may preclude adaptation. We conducted a genomic analysis to test the roles of genetic drift and divergent selection in causing genetic differentiation among populations of the island fox (Urocyon littoralis). This species consists of 6 subspecies, each of which occupies a different California Channel Island. Analysis of 5293 SNP loci generated using Restriction-site Associated DNA (RAD) sequencing found support for genetic drift as the dominant evolutionary mechanism driving population divergence among island fox populations. In particular, populations had exceptionally low genetic variation, small Ne (range = 2.1–89.7; median = 19.4), and significant genetic signatures of bottlenecks. Moreover, islands with the lowest genetic variation (and, by inference, the strongest historical genetic drift) were most genetically differentiated from mainland gray foxes, and vice versa, indicating genetic drift drives genome-wide divergence. Nonetheless, outlier tests identified 3.6–6.6% of loci as high FST outliers, suggesting that despite strong genetic drift, divergent selection contributes to population divergence. Patterns of similarity among populations based on high FST outliers mirrored patterns based on morphology, providing additional evidence that outliers reflect adaptive divergence. Extremely low genetic variation and small Ne in some island fox populations, particularly on San Nicolas Island, suggest that they may be vulnerable to fixation of deleterious alleles, decreased fitness, and reduced adaptive potential.;jsessionid=E985757F0B124995013927682B2A57BE.f04t04 
[Image: wildcat10-CougarHuntingDeer.jpg]
Island foxes may be 'least variable' of all wild animals

Date: April 21, 2016
Source: Cell Press

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This is a photo of a Channel Island fox.
Credit: Dr. Gary Roemer

In comparison to their relatives on the mainland, the Channel Island foxes living on six of California's Channel Islands are dwarves, at two-thirds the size. The island foxes most likely evolved from gray foxes brought to the northern islands by humans over 7,000 years ago. Some think island foxes may have been partially domesticated by Native Americans. Like many island species, they have little fear of humans.

Now a new study reported in the Cell Press journal Current Biology on April 21 finds that the foxes also show a surprising absence of genetic variation. The study offers the first complete genome sequences of an island species that is a model for long-term conservation of small, endangered populations, the researchers say.

"We find a dramatic reduction of genetic variation, far lower than most other animal species," says Jacqueline Robinson of the University of California, Los Angeles (UCLA).

One population in particular living on San Nicolas Island has an order of magnitude lower variation than any other known species, including the severely endangered African cheetah, Mountain gorilla, and Tasmanian devil, she says. Such near absence of genetic variation doesn't bode well for the foxes. But it also presents a puzzle as to how the foxes have managed as well as they have.

"The degree to which the San Nicolas foxes have lost genetic variation is remarkable, upholding a previous observation that they may be the least genetically variable population of wild animals known," says Robert Wayne, also of UCLA. "It suggests that under some conditions, genetic variation is not absolutely essential for the persistence of endangered populations."

The researchers sequenced DNA samples representing each of the Channel Island fox populations and one mainland gray fox from southern California. Researchers originally collected the island fox samples back in 1988, prior to subsequent population declines due to predation and disease in four of the island populations

Theory holds that small populations will not only lose variation, but will also accumulate deleterious variation as the normal process of natural selection fails. Indeed, the complete genomes of the island foxes show dramatic, 3- to 84-fold declines in heterozygosity. (Heterozygosity refers to places in the genome where an individual has inherited different variants of the same gene from their mother and father.) The foxes also show sharp increases in genes for which they carried two copies of a variant deemed to be harmful or deleterious in some way.

The San Nicolas Island population of foxes has a near absence of variation, the researchers report, demonstrating a unique "genetic flatlining." The only variation found in those foxes occurs at "heterozygosity hotspots," enriched for olfactory receptor genes and other genes with high levels of ancestral variation.

The researchers say the new findings need to be taken into careful consideration in plans for the foxes' future, including the removal of their federal endangered species protection status.

"The island fox populations suffer from both a lack of genetic diversity and the accumulation of damaging genetic variants, which is likely to worsen over time," Wayne says. Island foxes are also susceptible to population crashes from disease and non-native predators, such as golden eagles.

Additional research is needed to understand how the foxes may compensate for their decreased variation and the accumulation of deleterious variants. Wayne and Robinson say they'd like to explore gene expression and regulation in the foxes, to find out whether these factors may act to alleviate some of the effects of deleterious variants.

Story Source: Cell Press. "Island foxes may be 'least variable' of all wild animals." ScienceDaily. (accessed April 22, 2016).

Journal Reference:
Robinson et al. Genomic Flatlining in the Endangered Island Fox. Current Biology, 2016 DOI: 10.1016/j.cub.2016.02.062

•Genomic monomorphism on a scale not seen previously in eukaryotes is shown
•Deleterious variation and loss-of-function mutations are not purged
•Drift, without balancing selection, accounts for peaks of heterozygosity
•Persistence despite the absence of variation questions its role in small populations

Genetic studies of rare and endangered species often focus on defining and preserving genetically distinct populations, especially those having unique adaptations [ 1, 2 ]. Much less attention is directed at understanding the landscape of deleterious variation, an insidious consequence of geographic isolation and the inefficiency of natural selection to eliminate harmful variants in small populations [ 3–5 ]. With population sizes of many vertebrates decreasing and isolation increasing through habitat fragmentation and loss, understanding the extent and nature of deleterious variation in small populations is essential for predicting and enhancing population persistence. The Channel Island fox (Urocyon littoralis) is a dwarfed species that inhabits six of California’s Channel Islands and is derived from the mainland gray fox (U. cinereoargenteus). These isolated island populations have persisted for thousands of years at extremely small population sizes [ 6, 7 ] and, consequently, are a model for testing ideas about the accumulation of deleterious variation in small populations under natural conditions. Analysis of complete genome sequence data from island foxes shows a dramatic decrease in genome-wide variation and a sharp increase in the homozygosity of deleterious variants. The San Nicolas Island population has a near absence of variation, demonstrating a unique genetic flatlining that is punctuated by heterozygosity hotspots, enriched for olfactory receptor genes and other genes with high levels of ancestral variation. These findings question the generality of the small-population paradigm that maintains substantial genetic variation is necessary for short- and long-term persistence.

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