Natural History

The Japanese raccoon dog should be considered a distinct species from those on the mainland. It has a very different chromosome number.

The raccoon dog (Nyctereutes procyonoides) is a native of Asia.  The Soviet Union introduced raccoon dogs from the Russian Far East into several of its European and Caucasian Republics, and it is now well established in parts of Europe.

However, the exact taxonomy of raccoon dogs is quite fiercely debated.

There is some debate as to whether it should be classified as a basal canid that doesn’t belong to the Canini tribe (all true dogs and South American wild dogs) or the Vulpini tribe (all the true foxes) or whether it is actually a very primitive vulpine. I lean toward classifying it as a primitive vulpine, a classification it shares with the bat-eared fox (Otocyon megalotis).  The gray and island foxes (genus Urocyon) are true basal canids and belong to neither tribe, but the classification of these three species varies quite a bit in the literature.

But even more hotly contested than its position in the dog family’s phylogenetic tree is how many species of raccoon dog actually exist.

As regular readers of this blog know, I’m very skeptical of splitting species. For example, I have real issues with the current classification of the island fox, which lives on the Channel Islands of California, as a distinct species from the mainland gray fox. It has the same chromosome number as the mainland gray fox (2n=66). They are likely still interfertile, and their introduction to the islands may have occurred only through human agency.  Native Americans may have brought pet gray foxes to the islands, where they lived in semi-wild existence. Over time, they evolved into a slightly different kind of gray fox, which is smaller and somewhat tamer than those found on the mainland.

However, the Japanese subspecies of the raccoon dog (N. p. viverrinus) has a much different situation from its mainland relatives than the island fox has from the gray fox.

For example, the Japanese raccoon dog has much fewer chromosomes than the two mainland subspecies.  The mainland subspecies has 2n = 54, while the Japanese raccoon dog’s 2n=38.

That’s not a trivial chromosome difference.

Now, the ancestral raccoon dog colonized Japan just a little bit earlier than the island fox colonized its islands, but evolution has worked very differently in the case of the Japanese raccoon dog. No one has provided me any conclusive data that island foxes should be considered a distinct species, but this very wide chromosome number difference between Japanese and mainland raccoon dogs really sticks out.

Why on earth would anyone be so cavalier about calling island foxes a species and totally poo-poo the notion that Japanese raccoon dogs are?

That’s the decision of the International Union for Conservation of Nature Canid Group’s Canid Biology and Conservation Conference in 2001. This same group readily accepts the island fox as a species, but the Japanese raccoon dog has to be a subspecies.

Now, it’s likely that different panels of scientists are coming up with these decisions, but the cognitive dissonance between the decision to recognize the island fox as a unique species and deny the raccoon dog is more than a little bit troubling. Nie (2003) performed a chromosome map analysis on a Chinese raccoon dog, a Japanese raccoon dog, and a domestic dog and found that the Japanese raccoon dog really was quite distinct from the Chinese specimen.

Thus, the Japanese raccoon dog should be considered a distinct species (Nyctereutes viverrinus).

And it already has a fine common name to distinguish it from the mainland species. The Japanse call it the tanuki.

The evidence for this animal being a unique species is much stronger than exists for all the proposed new species of wolf that have been bandied about over the years. The Eastern wolf and red wolf of North America are actually wolf and coyote hybrids, and the genome-wide analyses have failed to find the uniqueness of Indian and Himalayan wolves, which were also proposed to be separate species based upon their ancient mtDNA lineages.

The tanuki shows that speciation can happen rapidly, especially when we’re talking about isolated island populations.  But just because an animal is stuck on an island for a couple of thousand of years doesn’t mean that it will evolve into a new species. The mutations and chromosome fusions that happened with the Japanese raccoon dog didn’t happen with the island fox.

But because they did happen with the tanuki, we ought to be more open to considering it a unique species.

The only thing that will settle this argument is if an in depth genetic analysis is performed, as was the case with the clouded leopard. There are now two species of clouded leopard, but until one of these analyses was performed, the exact taxonomy of the raccoon dog will be fiercely debated.  It is unlikely that the mainland and Japanese raccoon dogs are as genetically distinct as the mainland and Sunda clouded leopards, but having such extreme differences in chromosome number might mean that they are no longer chemically interfertile.

And if they aren’t, why on earth would we call them the same species?

Genome-wide analyses might even show that these two species split much earlier than is normally posited. The raccoon dog is considered  one of the most ancient extant evolutionary lineages in the dog family. It is possible that there were once many species of raccoon dog, and it might be that the Japanese raccoon dog, instead of evolving from the mainland species, is actually relic population of a species that has since gone extinct on the mainland.  The raccoon dog lineage may have included jackal-like animals, for specimens of a so-called primitive jackal that lived during the Middle Pleistocene in Northwest Africa were found to have skulls and dentition that resemble those of a raccoon dog.  Instead of being an ancestor of any living jackal species, perhaps this animal is actually a type of raccoon dog that evolved into something like a jackal.

Raccoon dogs are much more complex animals than we might realize. They may not be as charismatic as wolves are, but their evolutionary history and taxonomy have many questions that have yet to be answered.

But the bulk of the evidence suggests that at least two species of raccoon dog exist.

It’s just tough to change this paradigm.