Posts Tagged ‘Island Fox’

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pygmy three-toed sloth

Defining species and subspecies is a complex task. Lot of ink gets used in peer-reviewed journals debating if a population is a true species, a subspecies, an ecomorph, or a mere local variant. There is no cut-and-dry definition for any of these classifications, which is actually one of the strongest pieces of evidence for evolution. If all things were specially created, it would be very easy to determine species statuses. You wouldn’t have all this debate at all. It would be very easy to settle.

Long-term readers know that I’m skeptical of considering dogs a separate species from the wolf, even if it is not politically correct in some dog training circles to say so. I’m also skeptical of species status of the red wolf and the “Eastern wolf,” which are almost certainly just hybrids with wolves and coyotes. I’m skeptical that the Island fox of the California’s Channel Islands is separate species from the mainland gray fox, but I don’t deny that it is a very unique subspecies.

Part of my reasoning for being skeptical of the Island fox’s species status is that it only recently derived from the mainland species. These two populations have split from a common ancestor only within the last 9,200 years and may have been introduced to the islands by humans only about 7,000 years ago. For those of you keeping score, dogs split from their most recent common ancestor with wolves at least 15,000 years ago, and when you realize that there are some populations of wolves, especially in the New World, that are even more distantly related to dogs than the common subspecies of Eurasian wolves are, you can see where this gets really tricky.

So if I’m not calling a dog a species, then I really shouldn’t be calling an Island fox one.

If you call an Island fox is a species, then it is perhaps the youngest mammal species on earth.

The only other species that comes close to it is the pygmy three-toed sloth. That species derived the Panamanian brown-throated three-toed sloth about 8,900 years ago, when the island of Isla Escudo de Veraguas became separate from the mainland. Unlike their more generalist ancestor on the mainland, the pygmy sloth lives solely on mangrove leaves, and it spends a lot of time swimming from mangrove to mangrove.  It is 40 percent smaller than its mainland ancestor.

And there are only about 70 of them left.

This sloth and the Island fox are good examples of how rapidly simple barriers to gene flow can result in phenotypic divisions between related populations.

It is at this stage I realize that I have contradictions in my own concept of species. I think everyone who has looked at the issue does at some point.

I’m less willing to think of the Island fox as a species than the pygmy three-toed sloth. But the truth is they are both kind of in that nebulous area.

I’m pretty sure that if you caught a gray fox here in West Virginia and turned it out on the island of San Nicolas, it would mate with the island foxes. If it were a dog fox, I’m pretty sure it would dominate the island, not only because a mainland gray fox is quite a bit bigger than an island but also because these foxes are known for their very tight genetic bottleneck. These foxes have been able to keep their MHC haplotypes diverse and heterozygous because they have a way of picking up on these differences when they choose their mates. My guess is a big mainland gray would be in demand with just about any vixen on the island. Monogamy be damned.

But somehow, I think adding a brown-throated three-toed sloth to Isla Escudo de Veraguas would mess up the uniqueness of the pygmy three-toed sloth. Maybe the hybrids would be unable to live so well on mangrove leaves. Maybe.

Or maybe I’m just finding a way to rationalize it.

This isn’t an easy question. It’s not an easy answer.

We talk a lot about conserving endangered species, but the truth is we don’t have a very good concept of what a species is. We have a lot of different concepts for defining species– all of them good. But every single one of them leads to contradictions like these.

These contradictions are wonderful in science.  They give us things to question, debate, and explore.

But when we come up with something called an Endangered Species Act, what exactly do we mean?

The law cannot handle such nebulous and contradictory definitions. Science explores natural phenomena. The law derives requires clear definitions, or lacking such clear definitions, case law that fleshes out the nebulousness. (At least in common law countries…)

I don’t have any good answers to these questions, and the truth is that no one really does.

That’s because at the core of it, evolution isn’t just something that happened. It is something that is happening, and our human brains, which try to make clear distinctions so that we can understand, intuitively cannot handle the gray area.

We know that the Urocyon genus of wild dogs is a very distant offshoot from all other canids.  We know that three-toed sloths are not that closely related to two-toed sloths, which are the last survivors of the lineage that included those giant ground sloths that once roamed much of North America.

When we get to the finer distinctions between really closely related populations, we really don’t have good answers.

But it’s pretty clear that if we call the Island fox and the pygmy three-toed sloth species, they are very new ones.

Evolution can happen rapidly, but it usually doesn’t.

And islands have a way of making it happen fast.

Those concepts are fascinating in themselves– much more so on which Latin or Latinized binomial we use.

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San Nicolas island foxes (Urocyon littoralis) are thought to be least genetically diverse of all vertebrates. However, they have been able to maintain diversity and heterozygosity of their MHC haplotypes.

On my previous post entitled “Why is inbreeding bad?” I noted that one of the real issues with inbreeding is an impaired immune system as the result of losing diversity and heterozygosity in MHC/DLA haplotypes.

The MHC stands for the Major Histocompatibility Complex.  The MHC is cell surface molecule that is encoded by a relatively large gene family.  The MHC  molecule controls some of the actions of the leukocytes, “the white blood cells.”  As you might remember from your high school health class, leukocytes are the blood cells that act as police, taking out infectious diseases and foreign materials, including cancerous cells.

Possessing a greater diversity in MHC haplotypes allows the organism a heightened ability to control what leukocytes do when exposed to a variety of challenges to the immune system. Reduced diversity winds up restricting the immune system’s ability to fight disease.  Possessing a heterozygous MHC haplotypes also provides greater immune resistance than possessing homozygous MHC haplotypes.

In humans, the MHC is called the human leukocyte antigen system, usually abbreviated as HLA. In dogs, it is called the dog leukocyte antigen system, which is abbreviated at DLA.

One cannot look at an organism and tell what its MHC haplotypes are. It’s not like looking at fur or hair color.

And as a result, these haplotypes are very easily lost within a closed registry system.  Often, the haplotypes not lost entirely within a breed or strain, but because of the popular sire effect and continuous linebreeding  from “the best,” a huge percentage of the population in any one breed can be quite homozyous in its MHC haplotypes.

This has real health and welfare effects.  Autoimmune diseases are becoming more and more common in purebred dogs. Some breeds are highly susceptible to cancer, which might be partially the result of the decrease in MHC diversity of dogs within the closed registry system.  Allergies are also likely implicated to this reduction in MHC diversity and heterozygosity. The MHC also has some effect upon reproductive cells, which is one reason why certain breeds and strains have issues with fertility.

So what can be done?

Well, the easy answer is to do away with rigid closed registry systems and allow the different dog breeds to exist as very genetically diverse populations.

However, it is possible to breed for great MHC diversity in domestic dogs, even within the closed registry system.

To understand how this is possible, we will have to change species again.

Take the San Nicolas population of the island fox (Urocyon littoralis). This population is considered the least genetically variable of all sexually reproducing animals.

However, despite its lack of genetic diversity, this population of island fox has relatively diverse MHC haplotypes.

How does it do this?

Well, a study led by Andres Aguilar (2004)  found that the San Nicolas foxes likely were able to maintain their diverse MHC haplotypes through what is known as balancing selection. Balancing selection occurs when population keep multiple alleles actively maintained at frequencies that are higher than the mutation rate. It almost always happens within populations in better for an organism to be heterzygous for certain alleles than homozygous for them.

As we have seen with MHC haplotypes, it is better to be a heterzygote, so there is a strong selection pressure for the foxes to keep their MHC haplotypes diverse.

One way in which they likely do this is that they choose mates that have MHC haplotypes that are different from their own.

This might sound a little crazy, but even humans have innate mechanisms that are designed to keep our MHC haplotypes diverse.

There is a famous study in Switzerland that asked women which men were most attractive by smelling the shirts the men had slept in for two nights. Almost without exception, the women selected the men who had different MHC haplotypes from their own. The pheromones that are connected with sexual attraction in humans are also giving out genetic information such as what MHC haplotypes a potential mate might have.  And it’s so innate that women are able to obtain this information without understanding exactly what they are responding to.

It’s likely the same way in island foxes, which, like humans, typically reproduce within a bonded pair system. Foxes, like all wild dogs, are pretty particular about their mates. After all, the survival of their offspring is dependent upon having a partner that can provide for them.

Domestic dogs, for whatever reason, don’t seem to be as particular about their mates, and thus, it has been easier to selectively breed them.  Wolves and other wild dogs very rarely inbreed, but it is relatively easy to get dogs to inbreed and to do so for multiple generations.

And as a result, it has been easier for different breeds to lose their MHC haplotypes.

Further, it is not just the mere number of haplotypes a breed possesses. Heterozygosity has proven to be more important in determining immune health than just possessing a certain number of haplotypes.

That means that within an inbred population, there has to be some conscious effort to maintain both diversity and heterozygosity.

That is pretty hard to do when one is breeding for physical or behavioral traits– and the immune system genes cannot be readily ascertained.

Well, we do have a solution. Genoscoper currently offers an MHC II test, which would allow breeders to see what haplotypes their dogs posess and what to do with them. Mars Veterinary also offers a test that examines the MHC (among other things). It is called Optimal Selection from Wisdom Panel, and it was initially tested with breeders affiliated with the Dandie Dinmont Terrier Club of America (A NEW GENETIC BREEDING TOOL ON THE HORIZON (1)). Over a two year period, this selection tool has allowed Dandie Dinmont breeders to increase their litter sized from 2.75 to 4.0 puppies per litter. Dandie Dinmonts are a rare terrier breed that has issues with genetic diversity, and these tests could be a boon for breeds that have very small founding and effective populations.

So science now allows for us to do with domestic dogs what the San Nicolas island foxes were able to do on their own.  We can maintain relatively inbred populations and still keep the MHC haplotypes diverse and heterozygous.

However, here are some caveats:

First of all, virtually no dogs are bred without some eye to competition. Competition, whether in show or working trials, has a selection pressure of its own, and a breeder has to considered a wide variety of issues before choosing which dog to breed with which other dog. As I’ve noted before, MHC haplotypes are hard to see, so how many breeders would choose diversity and hetrozygosity of MHC haplotypes over the ability of the dog to win in the show ring or in the trial?  I would like to think that very few breeders would choose immune health over ribbons and titles, but that’s probably not the case.  Keeping the MHC diverse and heterozygous is a long-term project, and it requires a bit more dedication and discipline to breed for than physical or behavioral traits.

Further, breeders have to balance a wide variety of issues when selecting which dogs to breed, and MHC haplotype diversity alone should not be the sole criteria.  Other issues with temperament and hereditary diseases have to be considered in light of the MHC.

Finally, many of these breeds have either entirely lost MHC haplotypes or certain haplotypes are very rare within the breed.

You cannot do DIY balancing selection when you don’t have the haplotypes in the first place.

Even if we might have these tools, one should keep in mind that it is much more cost effective and easier to try to maintain genetic diversity within breeds and strains in the first place. It makes much more sense to keep breed registries more open and then operate selective breeding principles within much more diverse populations.  Breeding within much more diverse populations requires some understanding of how different traits are inherited, but one can readily learn these skills. It is not rocket science, but one can figure it out. If people living thousands of years ago0–before there was even a Mendelian theory of inheritance– were able to produce so many different types of dogs, then we surely can.

DIY balancing selection can be a tool within conservation genetics, but I think it has to be paired with a fundamental understanding of how population genetics works.

Otherwise, you’re going to get into silly arguments with people who think that you can just inbreed and inbreed without consequence. No rare dog breed can be saved in the long term if its immune system doesn’t work properly.

It’s really that simple.

In the end, selecting for diverse and heterozygous MHC haplotypes within a limited gene pool is less preferable than trying to maintain genetically diverse strain.  We have intentionally reduced genetic diversity within dog breeds and strains, yet as a population, dogs remain one of the most genetically diverse of all domestic animals. We have the ability to correct some of the errors without resorting to sophisticated genomic technology, but because the dog culture at large values purity and homozygosity at all costs, we are left looking at the only other option available.

Inbreeding requires so much scientific knowledge and acumen to pull off correctly that it really shouldn’t be done. And the validity registry systems that ultimately reduce dog breeds to inbred populations needs to be questioned.

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"Shhh! Don't tell anyone, we might not be a unique species after all!"

Jess from DesertWindHounds and I had a discussion yesterday on this post on BorderWars, which discusses the real lessons we need to learn from the Isle Royale wolves.

As these discussions tend to go, there was mention of the island fox (Urocyon littoralis) of California’s Channel Islands.  It is a particularly inbred animal, and those on the island of San Nicolas are thought to be the most inbred wild mammal population ever documented.

This discussion led to me voicing skepticism that island foxes were actually a valid species.

Yes, I’m aware of a mitochondrial DNA study that found that all island foxes have a very different mtDNA sequence from mainland gray foxes, and I’m also aware of a morphological comparison study that shows a great deal of variation between island and mainland foxes.

Neither of these studies actually tell us that these foxes actually represent a unique species.

Morphological alone studies can be confounding when we’re dealing with members of the dog family.  All members of the dog family have an unusually high number of tandem repeats in their DNA. These tandem repeats are responsible for some morphology, and because of how these tandem repeats operate, morphological variation can rapidly evolve. Using dental morphology alone, it was assumed that the South American bush dog was most closely related to the dhole and African wild dog. Genetic analyses have shown that the bush dog is actually closely related to the maned wolf, another South American wild dog.

So be skeptical of morphological studies when they relate to members of the dog family.

Mitochondrial DNA analysis, as I’ve shown time and again on this blog, can often be quite faulty.

The studies that point to an East Asian origin for domestic dogs have looked almost exclusively at mtDNA– lots and lots of different samples of mtDNA.

And yet, I don’t think we can find these to be all that conclusive, especially when the genome-wide analyses show that dogs show a very strong affinity with Middle Eastern wolves.

The problem with mtDNA analysis is that it looks at only maternal inheritance. Matrilines have a tendency of dying out.

If we take the Urocyon foxes, we actually have a very good reason for why matrlines would die out and then be replaced by another one.

I have not seen an mtDNA study that compares the island fox population to a very wide sample of gray foxes. Gray foxes range from the US/Canadian border to Venezuela.  Not only are they widespread, the gray fox lineage is the oldest extant lineage in the dog family.

With such a widespread and ancient lineage, it is possible that there could be wide mtDNA variance across the mainland population of the gray fox.  No one has actually looked at gray foxes this closely.

The island fox could be nothing more than an insular subspecies of the gray fox, but no one has produce convincing evidence one way or the other.

My hypothesis goes something like this:

California gray foxes colonized the Channel Islands and became separated from the mainland population. Over time, the mtDNA sequences on the mainland became replaced, while those on the Channel Islands were not touched.  My guess is that the gray fox’s heightened susceptibility toward distemper destroyed whole populations and entire mtDNA lineages over time on the California mainland. New foxes with different mtDNA lineages were able to colonize California following these outbreaks, and this could explain why California gray foxes and Channel Islands foxes have very different mtDNA sequences.

(A major distemper outbreak greatly reduced the population of gray foxes in Southern California in the mid-90’s. Gray foxes are a major vector for distemper, and if one lives where they do, it is a very good idea to make sure dogs are vaccinated for the disease.)

However, there are some hints.

Jess pointed me to a new analysis that did some more sophisticated carbon-14 dating on the earliest fox fossils on the Channel Islands. These fossils were dated to a much later time than the 10,400 to 16,000 years when it was proposed that the ancestral gray fox came to the Channel Island.   The earliest proposed date from that study is 6,400 years ago, which is thousands of years after humans colonized the islands– and thousands of years after any of the islands were connected to the mainland.

If this later date is more accurate, then it means that the island fox was introduced to the Channel Islands– probably as a pet or semi-domesticated animal. Isotopic analysis revealed that the foxes ate almost nothing but marine life, which they would have obtained from the human companions.

It was not unusual for Native Americas to keep wild dogs as pets. The gray fox was a relatively common pet in some cultures, and on the exotic pet market, one sees gray foxes offered as being more tamable than red foxes.

Now, one should be a little bit cautious of studies that use carbon-dated fossils to tell us when animals arrived. It is possible that the 6,400-year-old fossil is just the oldest fox fossil that has been discovered. Genetic evidence shows that the dingo arrived in Australia earlier than its oldest fossil remains, so it is possible that the foxes came to the islands at an earlier date than the fossils are suggesting.

However, if this later date is correct, the island fox is a gray fox– and it is an old introduced species.  Something like the dingo of the Channel Islands.

The authors of this later study are curious about how quickly a fox could become dwarfed on islands, but as we have seen with so many dog species, morphological variation can evolve very rapidly. Not only do we have the tandem repeat issue, we have discovered that the genes that separate the many different breeds and types of domestic dog are controlled by just slight variance on just a few genes. Similar results have not been confirmed in modern village dog populations, but breed dogs vary from each other by only very tiny genetic variations.  Small size, for example, evolved very soon in the development of the domestic dog, and many modern small dogs have a variant of gene that causes small size that is also found in some Middle Eastern wolves.

Even the older dates associated with the split between island and mainland gray foxes are really recent.  10,400 to 16,000 years is actually much sooner than the date proposed for when dogs and wolves split from each other. The study that sequenced the dog genome revealed that the dog and wolf lineages began to split 27,000 years ago. The first mtDNA studies suggested that dogs and wolves split 135,000 years ago.

It is now nearly impossible to say that dogs and wolves are not the same species– and those who try cannot do so without twisting themselves into severe logical pretzels. But if it is now accepted that dogs and wolves represent the same species, why on earth would we assume that island foxes are a separate species when the split from their mainland ancestors such a relatively short time ago?

In order to resolve this issue, we need in depth analyses of nuclear DNA from gray foxes from a variety of locations and from island foxes.  As the authors of the recent carbon-14 study state, we also need to see if we can find ancient DNA in the old fox bones from the Channel Islands. Only when we get a really broadly-based analysis will we be able to see where island foxes fit.

My guess is the reason why such studies have not been performed is that it is just not a major priority among geneticists. Gray foxes themselves are not widely studied, and although they have been confirmed as canid lineage that dates back 10 million years, they just aren’t that interesting to most scientists.

Also, I don’t think the results of such studies would be received very well.

In all likelihood, the island fox will turn out to be a subspecies.

Subspecies can get special protection– see the Mexican wolf and Florida panther–but it’s easier to protect an endangered species under the Endangered Species Act when it is actually a species.

Now, it may be that if the island foxes are just a subspecies, they can experience some amount of genetic  rescue through the introduction of mainland gray foxes to the island.   The problem is that if that happens, the mainland gray fox genetics will spread through the population, just as the male wolf that colonized Isle Royale wound up swamping the inbred population with his genes.  The foxes on the islands would lose some of their unique morphology, although one should not assume that they would become larger. Gray foxes native to Central and northern South America are not much larger than the island foxes, and foxes from these populations would probably be the best choice for an outcross.

But if genetic rescue is attempted, one runs the risk of losing an inbred population of foxes that are able to produce pretty interesting data. The heavily inbred San Nicolas population has rather diverse MHC haplotypes– the result of balancing selection.

It’s much easier for science to operate under the assumption that Urocyon littoralis is a unique species.

It probably isn’t.

That’s my wager.










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It is an island fox (Urocyon littoralis). It is the only other species in the genus Urocyon besides the gray fox. It looks very similar to that species, but it is quite a bit smaller. The normal gray fox of the mainland weighs 8 to 15 pounds, while the island foxes weigh only 3 to 6 pounds. The island foxes have significantly shorter tails in proportion to their bodies than the mainland gray foxes do, which is one reason why they are sometimes called “short-tailed foxes.”

It is often claimed that the island fox is the second smallest of all wild dogs. Only the fennec fox is more diminutive. However, I have a little trouble verifying this claim, but I will say that the island fox is very likely the smallest canid in the New World.

The animals are found exclusively on the Channel Islands of California. Six of the eight islands have foxes, and each island has its own unique subspecies. Each is a little bit different from the other, but one of the main differences between the different subspecies is the number of vertebrae in the tail.  They also differ in their markings.

The foxes are believed to have colonized the Northern Channel Islands 10,000 to 16,000 years ago. Lower ocean levels during the last ice age allowed the foxes a better opportunity to visit the islands in search of food. In fact, they weren’t really visiting the islands. The were visiting a single large island that now makes up the four northernmost islands.

As the sea level rose, the foxes from those three larger islands in the northern part of the archipelago became isolated from each other. The single large island had become four. Anacapa Island had no fresh water on it, so it could not support a population of island foxes.

Okay. That explains how the foxes got to the northern islands.

But what about the southern islands? After all, those islands aren’t very close to those northern islands that the foxes first colonized.

Well, there is a thing about animals that evolve on islands. If there are few major predators, the animals become very docile and curious. There simply is no reason to be scared of anything. It is a dangerous development, of course, because one can easily make a list that have either gone extinct or are endangered simply because they evolved into fearless and docile creatures.

Island foxes are a good example of what wild dogs are like when they evolve without persecution from man. Unlike wild gray foxes on the mainland,  these foxes are not extremely afraid of people.  Most wild dogs, if not victims of  generations of persecution, are actually quite curious about our species. For some reason, we catch their fancy, even if it is just an excuse to beg food.

These foxes had a relationship with the Native Americans who lived on the islands. They were most likely kept as pets, and the foxes were then carried from island to island. It is believed that these foxes colonized the southern islands through human introduction.

The San Clemete fox began to separate into its own subspecies in the past 3,000 to 4,000 years. The San Nicolas subspecies is believed to be only about 2,000 years old, and the Santa Catalina subspecies is the most recent. It may have evolved as recently as 800 years ago.

The foxes are critically endangered. Introduced species have had a negative effect on the island fox population. Cats compete for the foxes for food. Grazing animals have diminished some of the foxes’ habitat. The grasslands and the chaparral are not exactly as they once were. The land is now much more eroded, and the foxes are more exposed than they once were.

Among these grazing animals are a herd of bison that a Hollywood film crew introduced as living props in a Western that was filmed there. The status of these animals is quite controversial. Virtually all orthodox conservationists want them removed. However, the tourists love them, and because tourists love bison and tourists bring money, the bison remain.

The real problem these foxes face comes from predation from golden eagles.  On the northern islands, the number one reason for fox mortality is the golden eagle.

Yes, and we know that golden eagles are a protected species. And they are native to California.

The foxes have thrived on their islands when there were tons of golden eagles in the vicinity.

Why would the foxes now suffer from golden eagle predation?

Well, the answer has to do with several actors on the island ecosystem.

Originally, golden eagles almost never came to the Channel Islands. Those islands don’t have enough prey to tempt them from the mainland. Furthermore, the islands were home to bald eagles, which do not tolerate golden eagles near their nests. Bald eagles eat mostly fish and were no major threat to the foxes.

When the bald eagle population crashed last century, the golden eagles didn’t have to worry about intruding on their territories anymore.

However, they still did not start colonizing the islands until the golden eagles discovered that there were large numbers of feral pigs on the island. Feral piglets are a good food source for a bird of prey, and they soon colonized the island, living almost exclusively on piglets. However, they occasionally caught foxes, and because the foxes had evolved without much selective pressure from predation, even just a little predation has proven disastrous.

Conservationist have tried to mitigate these problems by killing off of feral pigs, but the eagles still persist. It is now believed that the only way to take care of this problem is to remove the golden eagles from the islands.

And then there is the problem with the San Clemente loggerhead shrike. This is an endemic subspecies of the very common “butcher bird” of the mainland. However, it has suffered greatly from introduced species. Rats and feral cats have taken their toll on shrike numbers.

Island foxes also raid their nests, so it is been decided that something must be done to prevent the foxes from preying upon shrike nests.

Because the foxes are critically endangered,  it was decided to use non-lethal methods. The most successful of these involved the use of e-collars. The foxes were all captured and fitted with the collars. Whenever, a fox approached a shrike nest, it would be shocked. Very quickly, the foxes learned to avoid the areas where shrikes were nesting.

Everything about these foxes has proven to be unusual and complex. Not only do they own their current distribution to the actions of man, they currently owe their survival to our understanding a complex island ecosystem. We are only just now figuring out how to do it, and even then, it is a daunting challenge.

But we will get there.

Let’s hope so.


Any time we are dealing with the genus Urocyon we must remember that we are looking at a living fossil. Both species in the genus represent what is generally believed to the be one of the oldest– if not the oldest– extant form of wild dog. They have many primitive traits, not the least of which is their ability to climb trees almost as well as any cat.

I should also note here that the island fox is thought of as a separate species from the more common gray fox for some rather interesting reasons. It has not been reproductively isolated from the mainland very long. Indeed, they can still crossbreed, and it was recently found that the island fox has nearly identical mtDNA sequences with the gray foxes of Southern California.

Its status as a full species bothers me a bit.

This is particularly true, when you understand that I am adamant that dogs and wolves represent a single species. The differences between an island fox and a gray fox are nothing compared to the differences between a chihuahua and an arctic wolf.

Dogs and wolves separated a long time ago– much longer than the paltry 10,000 years that exists between mainland gray and island foxes.  The original mtDNA studies found that they separated over 100,000 years ago.  Current consensus now says that this happened anywhere from 15,000 to 40,000 years ago. That’s still alonger than island foxes have been separated from their mainland cousins.

This gets even more interesting. If one takes into account how widely distributed the mainland gray fox and how variable it is in appearance, then one could see that there might be room to count the island gray fox as a subspecies.

Keep in mind that the gray fox is very widely distributed. Its range includes areas in Canada very close to the US border, and from there, its range extends south through Mexico and Central America to Colombia and Venezuela. Most people are unaware of the gray fox’s wide distribution.

And throughout its range it varies in appearance. The smallest individuals are half the size the largest ones.

So one could theoretically put the island fox within the same species as the gray fox. It would fit nicely with the diversity that exists within that much more common species.

However, it is also useful to understand the island fox as a species. It has a very different lifestyle than virtually all of its mainland cousins. It lives on an island where it is the largest mammalian predator. It has evolved without significant predation as a selective pressure on its behavior.

Behaviorally and ecologically, it is quite unique.

And thus, I am still conflicted about how I would classify this animal.

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Let’s say we have an island with two endangered species living on it. This situation isn’t hard to imagine. Lots of islands have their own endemic native species that are very often endangered. Most island jurisdictions do all they can to protect their endemic wildlife.

But here’s the twist: Let’s say it has been determined one of those endangered species might be a major factor for mortality in the other endangered species. What do you do?

Well, we do have a real case in which one endangered species is harming the population of another. On San Clemente Island, the local subspecies of the island fox is preying upon an endangered subspecies of Loggerhead Shrike.

In the 90’s, it looked like the San Clemente Loggerhead Shrike was on its way to extinction.

Because the foxes are also quite endangered, there was little that could be done to reduce fox numbers.

However, a plan was devised and implemented in 1998 to solve the fox predation problem. The first part of this plan was to trap the foxes and hold them until the shrike breeding season was over. The second part involved the building of an electric fence around the shrike nests.

But the third part of the plan was the most novel.

E-collars have been part of dog training for a very long time. These collars are often employed to keep dogs from running deer and to generally control predatory behavior. A similar collar is also used as an invisible fence to contain dogs to their owners’ yards.

It was decided that these collars could also be used to train the foxes to leave the shrikes alone.  The foxes were trapped and fitted with e-collars that could be activated when they approached an antenna sensor. It was the invisible fence to protect the shrikes. If a fox approached the trees where the shrikes were nesting, it got shocked. (These foxes, like their mainland relatives, can climb trees to raid bird nests.)

When this three pronged plan was implemented in 1998, the shrikes had a successful nesting season, and no foxes had to be killed to save the shrikes– thanks to a little “shock therapy.”

(In case you didn’t know, island foxes are native the Channel Islands off the coast of California. They are very closely related to the more common gray fox.)

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Video is here.

Swift foxes are prairie animals. They went extinct in Saskatchewan, Manitoba, and Alberta because of the practice of lacing carcasses with strychnine and other poisons to kill wolves. These poisons would kill any animal that scavenged the carcass, including swift foxes.  There are several other reasons listed here. The decision of Canada to tame its prairies for agriculture made it an inhospitable place for the swift fox.

The Smeeton fox breeding mentioned in this video is now run as a private organization. Their daughter, Clio, is probably the world’s greatest authority in swift foxes. The use of tribal lands in this part of Canada has been key to restoring them to the wild. Also, they have bred the foxes in open air pens, where they are occasionally preyed upon by hawks. This predation teaches the kits to avoid birds of prey, a very useful skill in the wild. However, I don’t know how any fox can learn to avoid coyotes from a captive situation.

These foxes are really interesting. Its scientific name is Vulpes velox, placing it in the genus of the “true” foxes, including the red fox.  It has a very close relative called the kit fox (Vulpes macrotis–“big eared fox”). It ranges into the deserts of the United States– Southwest and Great Basin– and Mexico. Its range is a bit west of the swift fox.

At one time, they were considered conspecific. Indeed, they have interbred and produced fertile offspring. Some people refer to the swift fox as a “kit fox,” but the current thinking of taxonomists is to place them as separate species.

Interestingly, their closest relative is the Arctic fox, with whom they both share the same number of chromosomes and a common ancestor within the last 250,000 years. However, the Arctic fox is usually classified in its own genus called Alopex.  This genus exists because the early taxonmists relied upon morphology alone to determine relationships between animals. The Arctic fox had a skull that was broader than a typical fox in the genus Vulpes but narrower than a dog’s skull. So it had to be a separate genus.

Now, we know that Arctic foxes are really closely related to the kit and swift foxes. In fact, if you look at white form of Artic fox in the summer and compare to the swift fox above, you can see a very strong similarity. (White Arctic foxes are brown with cream-colored patches on their necks, chests, bellies, and tails. They turn white in the winter. Blue Arctic foxes are silvery black in the summer months or silvery black with white markings. They turn a grayish blue color in the winter.)


White Arctic fox in summer. Compare with the swift fox above.

No one would have ever thought that the desert dwelling kit fox and the Arctic fox were such close cousins. In fact, it was only when fur farmers in Scandinavia crossed “blue foxes” with “silver foxes” that science began to realize the taxonomy wasn’t quite right. Blue foxes are the blue phase of Artic foxes, which are highly prized for their fur. Silver foxes are melanistic red foxes that have interspersed gray hairs on their coats, giving them a silver appearence. These hybrids were infertile, but it raised the question about whether the Arctic fox was truly a separate genus from the other foxes.

As far as I know, no one has tried to cross an Arctic fox with a Swift or kit fox, but it is probably possible. It is also possible that they could produce fertile offspring from the cross. However, kit and swift foxes aren’t fur farmed animals. There are no “domestic” strains of these foxes, unlike the various domestic forms red fox (including the truly domesticated foxes of Russia) and the farmed variety of blue Arctic fox.

Of course, I’m sure the first people to lay eyes on a swift or kit fox thought that it was a gray fox. However, the animal called a gray fox in North America isn’t even closely related to the true foxes. It is gray, just as the swift and kit foxes are, but it is an entirely different animal. It is the oldest canid in the Americas, and it may be the oldest canid in the entire world.

Its closest relative can be found on the Channel Islands. This species of fox is called the island fox, and it resembles a very small gray fox. How it got to the islands remains a mystery, but one theory is that it arrived there as a pet belonging to the native peoples of Southern California. Because it was living on the islands, where food was somewhat scarce, the fox became smaller and smaller to make better use of these limited resources. Today, it is a highly endangered animal.  These two foxes are not closely related to the others, and they aren’t related to any of the South American “wolf-foxes” either. They are an evolutionary relict of what the first wild dogs may have looked like.

The swift, the kit, and Arctic foxes should probably be placed in the same genus, which the share with the other Vulpine foxes, including the well-known red fox. The fact that we are only just now figuring out where these animals fit into their proper taxonomy and evolutionary history shows the limits of using morphology alone to determine these relationships.

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These foxes were filmed in Pennsylvania.

Grey foxes and raccoon dogs are the most primitive of wild dog species. They both retain their ability to climb trees. All dogs derive from tree climbing ancestors. Most dog species have developed in to carnivores that run on the ground and have lost this ability.

Grey foxes are in their own genius. The mainland grey is the most common species, but two other species exist, although one may be extinct. The island fox lives on the Channel Islands off the Coast of Southern California, where each island has its own subspecies. The foxes have suffered as introduced species have come to the islands. One population of these foxes was destroyed when the bald eagle population crashed. The bald eagles kept the golden eagles off the island. Bald eagles are mainly fish predators. Golden eagles eat foxes, and as soon as they colonized the islands, they began eating the foxes.

Cozumel fox is also a close relative, but it may already be extinct. It lives or lived on Cozumel, Island in Mexico.

The mainland grey fox has a wide range. It is sometimes spotted in Canada, especially Southern Ontario and the parts of Quebec that border on New York and New England. It also has been found in southern Manitoba. It also is found in American Southwest through most of Mexico. It is found on the Pacific Coast of Central America, and populations exist in Colombia and Venezuela.

An article on the grey fox can be found here.

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