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Posts Tagged ‘hybrid species’

The notion that the black cats of parts of northeast Scotland are hybrids between Scottish wildcats and domestic cats is not controversial. The idea that they represent a hybrid species is, however, not something that has been considered. 

These black cats were anomalous, and during the tabloid-soaked years of the 1980s and 1990s, they became sort of legendary throughout Britain.  Eventually, some analysis was performed on some specimens, and it was decided that these animals represented hybrids between domestic cats  and Scottish wildcats. At the time,  these two animals were considered different subspecies but belonged to the same species.

Since that time, a new revision of felid taxonomy has been proposed in which the European and Caucasian wildcats are placed in one species (Felis silvestris) and the species that gave rise to the domestic cat is now called Felis lybica.  I generally agree with this new taxonomy, because of the deep division molecular division between these two cats, but I think that the domestic cat belongs as as part of Felis lybica in the same way dogs are part Canis lupus

If one adheres to this revision and accepts my little critique, then the so-called Kellas cats represent a hybrid species.  It would be great if more molecular studies were performed on these cats, but cats don’t seem to get as much fanfare or funding as dogs do when it comes to these sorts of studies.

I should also note that the Scottish population of European wildcats has significant introgression from domestic cats, so much so that in past 30 years, no Scottish wildcat DNA samples have shown to be free of domestic cat genetic markers.

If one defines a species as having no other crossed in, then we could say that Scottish wildcat is extinct in the wild, but we know that countless species exchange genes with close relatives,

This ecotype of the Lybica wildcat is much more adapted to the Holocene world than the European wildcat ever was. It is more than at home in agrarian landscapes, and it does well in urban environments too.

This story sort of parallels our own species, which came out of Africa into the land of the Neanderthals. We exchanged genes, but our species eventually swamped the land.

Maybe we will have better DNA studies of cats. Maybe we’ll find that European and European-derived domestic cats have traces of European wildcat ancestry.

One should have little hope for the pure European wildcat existing in Scotland or anywhere else where it currently roams, but maybe if we’re okay with the simple fact that hybridization exists, we can preserve what looks and behaves like a wildcat– and not worry too much about its DNA.

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The edible frog exists only as an F1 hybrid between the pool and marsh frog. It’s a good example of a hybrid species.

One of the real problems we have in discussing whether a population of animals is a species or not is that we have several concepts that make the whole issue quite murky.

One of these concetps is the concept known a “hybrid species.”

It is certainly true that hybridization can create a new species, and it is certainly true that hybridization between related species is not as uncommon in the wild as was commonly thought.

These two issues make concept of “hybrid species” fairly murky.

For example, in the last few years, we have discovered that modern human populations, though derived from a species that originated in East Africa, occasionally hybridized with other human species, including Neanderthals.  A tiny part of the genome of any humans whose ancestry is not within sub-Saharan Africa is Neanderthal.

Does that tiny bit of Neanderthal make us a hybrid species?

Many coyotes, especially those living in the East, have a little bit of dog and wolf DNA. They are still overwhelmingly coyote in their genetic make-up, but they do have some genetic material from another species.

Does that make them a hybrid species?

I don’t think we can say that Eastern coyotes and modern humans are a hybrid species. These organisms just happen to contain genetic material from another species, and in that same vein, I don’t think the red wolf counts as a hybrid species either. It is a coyote with some wolf genes, in the same way I’m a modern human with some Neanderthal genes.

After all, the red wolf wouldn’t exist at all, if humans weren’t actively keeping them from breeding with coyotes, which should be a major red flag about the unique species status of this animal.

I think a true hybrid species can exist with larger mammals, with the possible exceptions of the mule deer and Pere David’s deer. European bison may also be hybrids between ancient Eurasian bison and the aurochs.

But there actually are species that exist only in a hybrid form.

Perhaps the best example of this hybrid form is the European edible frog (Pelophylax kl. esculentus).

It is a hybrid between the pool frog (Pelophylax lessonae) and the marsh frog (Pelophylax ridibundus).

And the hybrid form cannot breed true. If you breed two edible frogs together, the tadpoles are too deformed to survive.

However, the edible frog can interbreed with either parent species, but the resultant offspring are very similar to the parent species on which there has been a doubling up.

The “kl.” in the edible frog’s scientific name stands for “klepton.”

A biological klepton is  “a community of populations with a hybrid genome derived from the same parental species, reproductively dependent upon sympatric species that play the role of sexual host.”

These animals are not uncommon in fish and amphibians.

I’ve never heard of one in mammals or birds, though I’m sure someone more knowledgeable than I am might have some examples I don’t know about.

We need to have a better way of defining a hybrid species.

An organism that has some genetic material from a related species that got there as a result of crossbreeding is not a good example of a hybrid species. My guess is that when we get really sophisticated genomic analyses, we’re going to find that virtually every mammal species has some genes from related species that got there through some very limited and very distant crossbreeding.

But does that mean they are hybrid species?

I really don’t think so.

Real hybrid species do exist, and hybrid speciation is one of the most under-valued ways in which species can come into being.

It’s just that we need to be careful about making these declarations about a new species being formed through hybridization. Yes, it does happen, but if we’re not careful, we can wind up creating a definition of a hybrid species that essentially becomes meaningless.

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A French veterinarian named Dr. Sauvel shot this kouprey in Cambodia. He made a trophy out of the horns and displayed them at his home in France. The French zoologist Achille Urbain discovered the horns at Sauvel's home and thought they might represent a new species. He would later use this discovery to confirm that a wild cow brought over from Cambodia was actually a unique species, which he called the kouprey and named Bos sauveli in honor of the veterinarian who shot this specimen.

Some people might be a little surprised with the findings of a recent study that showed that the s0-called red wolf is nothing more than a coyote with some wolf ancestry. Because the Eastern US is full of coyotes with wolf ancestry, one might be open to questioning the validity of the red wolf as a unique species– much less an endangered one.

I think the bulk of the evidence shows that the red wolf as we know it now is a contrived species.  The so-called red wolves of earlier times may have been the original eastern population of coyote that was exterminated along with the wolves that were native to the same region.  And the so-called Eastern wolf species has been found to be a wolf with some coyote ancestry. What we’re calling an Eastern coyote today is primarily Western coyote with some wolf and dog crossed in.

Both of these animals are derived from hybrids that existed in the wild. The wolves of the western Great Lakes region had coyote genes introduced into their populations 600 to 900 years ago, but the vast majority of these animals would not have existed had Western man not killed off all the wolves in the East.

As difficult as it is for people to accept, the Eastern wolf and the red wolf likely are not valid species. One is a wolf with some coyote genes, and the other is a coyote with some wolf genes.

However, there have been cases in which an animal was declared a hybrid, but then later studies revealed actually to be a unique species after all.

Probably the best example of a hybrid origin being falsified in recent years is the kouprey.

The kouprey is a wild cattle species that lives primarily in Cambodia, but it can also be found in adjacent parts of Laos and Thailand.

If you’ve never heard of a kouprey, it’s because they are very rare, and they were only described to science in 1937. A French zoologist named Achille Urbain discovered some unusual horns that were mounted as a hunting trophy in the home of a veterinarian who had worked in Cambodia. After examining the horns closely, Urbain thought that they might come from a new species.  One animal wound up at the Vincennes Zoo in Paris, which Urbain used as his holotype specimen. Later, Harvard zoologist Harold Jefferson Coolidge would elevate the kouprey to its own genus, which he called Novibos (“the new ox.”)

It was the last of the cattle species to have been documented by science, and it was one of the last large species of land mammal to have been documented.

For decades, it was treated as an enigmatic species of wild cattle. The Cambodian people recognized the uniqueness of this animal, which occurred almost exclusively within their nation’s borders, and they declared the kouprey to be their national animal.

Lots of romance and national identity was tied up in the kouprey.

Then, in 2006, Northwestern University biologist Gary Galbreath co-authored an article that revealed that the kouprey was nothing more than a cross between the zebu (indicus domestic cattle species) and the banteng, a much more common species of cattle that is native to Southeast Asia and also exists as a domestic animal.  This zebu/banteng hybrid then went wild in the Cambodian forest.

Galbreath’s study compared mitochondrial DNA fromCambodian banteng and two captive kouprey from a Cambodian wildlife rescue facility.  This study merely examined the cytochrome b gene, but it found that the two kouprey were actually very similar to the banteng.

This study went out into the popular press as declaring the kouprey an entirely made-up species.

However, not everyone was so convinced.

Galbreath’s claim was a major affront to a major paradigm within bovine taxonomy.

So it needed a more in depth analysis to see if the hybrid origin theory for the kouprey was actually true.

Two French zoologists, Alexandre Hassanin and Anne Ropiquet, analyzed three mitochondrial DNA regions and five nuclear DNA fragments that represented 4582 nucleotides.  They found that kouprey have nuclear DNA that is quite distinct from banteng or zebu, and the reason why Galbreath received such a close overlap between Cambodian banteng and kouprey is that the banteng of Cambodia have hybridized with kouprey.  Somewhere along the line, a domestic banteng bull mated with a kouprey cow, and the descendants of these hybrids comprise a large proportion of the banteng in Cambodia.  A fossilized skull of a kouprey was also discovered that was dated to the Pleistocene or early Holocene– well before indicus cattle were domesticated.

Galbreath has since rejected his initial findings.

This study that looked at nuclear DNA in the kouprey looked at much smaller part of the genome than the study that found no evidence for an Eastern wolf species and found the red wolf to be predominantly coyote in origin.

Yet this study very quickly discovered that the kouprey has very unique genetic markers.

This study very clearly falsified the hypothesis that the kouprey was derived from a hybrid between indicus cattle and the banteng.

That has not happened with the red wolf or the Eastern wolf. Indeed, the study that found them to be hybrid in origin was perhaps the most in depth analysis of wolf and coyote nuclear DNA ever performed.

It is possible to falsify the hypothesis that organisms are hybrid in origin.  In the case of the red wolf and the Eastern wolf, it has not been.

But in the case of the kouprey, it clearly has.

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I would be remiss if I didn’t say that no one has seen a wild kouprey since 1983.

They may very well be extinct in the wild.

So I guess it’s good to know that this animal actually was a valid species.

But that would have been nicer to have known while they were still relatively common.

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