Natural History

So I’ve been sent this story a couple of times: apparently, a genetic analysis of Galveston Island coyotes found a relationship between these coyotes and what are called red wolves that are part of the US Fish and Wildlife Service’s endangered species recovery program.

I found it interesting that Bridgett vonHoldt was part of the study that found this genetic link between Galveston Island coyotes and red wolves. VonHoldt is one of the leading canid molecular geneticists who was part of a team of researchers that have found that the red wolf is of hybrid origin. She was also an author of the paper that shows the biggest problem that the red wolf has in claiming species status.

This problem is that it really doesn’t matter whether red wolves are hybrids or not. The question is whether they are hybrids between two entities that are best described as distinct species or not.

A comparisons of full genomes of gray wolves, Eastern wolves, red wolves, and coyotes revealed that Eastern wolves and red wolves are hybrids between coyotes and gray wolves. This finding has been revealed in three papers, one in 2011, one in 2016, and one in 2018. This hybrid discussion is tiresome, though, because we can get into a sea-lioning contest about how there might very well be a hidden unique red wolf species hidden somewhere in the coyote.

This paper would appear to have found such a thing, but it needs to be understood within the full context of the literature.

Yes, the genome-wide and full genome comparisons reveal a hybrid origin of red and Eastern wolves, but the problem that no one seems to be willing to deal with is how recently gray wolves and coyotes split.

When it seemed like gray wolves and coyotes had a common ancestor 800,000 to a million years ago, debates about hybrid origin made some sense. But in the 2016 study, the authors did some comparisons of gray wolf and coyote DNA to see if they could find when the two forms of canid split. The most statistically valid date for that common ancestor was alive around 50,000 years ago:

If we assume a generation time of 3 years, and an effective population size of 45,000 (24, 25), then this corresponds to a divergence time of 50.8 to 52.1 thousand years ago (ka), roughly the same as previous estimates of the divergence time of extant gray wolves (26–28). Thus, the amount of genetic differentiation between gray wolves and coyotes is low and not much greater than the amount of differentiation within each species (for example, Eurasian versus North American gray wolf, FST = 0.099; Table 2 and fig. S1).  This result contradicts molecular clock calculations based on short mitochondrial control region sequences, which were calibrated using a 1-Ma (million years ago) divergence time between gray wolves and coyotes (10). Despite body size and other phenotypic differences between the two species [for example, (1)] and a long history of coyote- and wolf-like forms in North America (1, 29), the genomic data suggest that modern coyotes and gray wolves are very close relatives with a recent common ancestry. (Italics mine).

This paper shows that what we call a coyote could best be described as a form of gray wolf, a smaller and more jackal-like form of gray wolf to be sure but a gray wolf nonetheless. I don’t know why the authors didn’t make this suggestion, because a similar way of thinking clearly puts pugs and Newfoundlands in the gray wolf species as well. This classification is controversial, but it’s not that controversial if you understand systematics based upon clade-based thinking.

So what the researchers found Galveston Island is a population of coyotes that share some genetics with the red wolf. The population that founded the red wolf population that receives conservation attention came from the East Texas and Louisiana mainland, and if this population is isolated, then you can see how this unique population could have retain its genetics as more coyotes spread through the mainland on their way East.

Even if we were to find that there were once large wolves in Prehistoric North America that had coyote-like mitochondrial DNA, we would still have that problem of the recent coyote origins. The only way that problem might be solved is if these large wolves are significantly older than the date suggested from the gray wolf-coyote split. Because we know that anatomically modern gray wolves already existed in Eurasia well before the coyote-gray wolf split, one would expect to find large wolves with coyote-like DNA in North America. We also should expect to find wolves with coyote-like DNA in the Old World as well.

The real debate should be about the validity of Canis latrans as a species. The problem with going down this road is more political than scientific. Coyotes are the most successful relatively large canid in North America. They are found in 49 states, and the only reason they aren’t in Hawaii is they can’t swim that wall.  They are working their way down through Panama, and I would not be surprised if I read some morning that they had crossed the swamps of Darien into Colombia.  Coyotes receive almost no protections anywhere in their range, while wolves generally are protected via the ESA where their populations have been reduced or extirpated.

But we don’t regard domestic dogs as a species either. One can easily see them as a divergent form of gray wolf without losing perspective that there really ecological distinction between a domestic animal and a top-level predator. We are currently grappling with the evidence that dog genes are introgressed heavily into Eurasian wolf populations, but almost exactly the same thing has been observed with North American wolves and coyotes. Even the wolves of Alaska and Yellowstone have coyote ancestry.  

So one should have a bit of skepticism about what was actually discovered on Galveston Island.  At the very least, we should be very careful about thinking of gray wolves, dogs, and coyotes as hard and fast entities and that all three continue to exchange genes across their respective ranges.

We do have a species problem, a species problem that would make sense only if Darwininan precepts are true. With this clade in Canidae, we have also have the Ethiopian wolf, the African golden wolf, and the Eurasian golden jackal that are capable of exchanging genes with each other and with dogs and Holarctic gray wolves. Indeed, the African golden wolf is derived from either a gray wolf or a gray wolf ancestor interbreeding with the ancestral Ethiopian wolf, which was probably much more widespread in the past. 

I don’t have as much of problem thinking of coyotes as a form a gray wolf, probably because I’ve long since accepted that domestic dogs are also a form of gray wolf, but thinking in this way is disruptive to our concept of hard and fast species. However, we should never think that such thing as a hard and fast species exists in the first place. Evolution is fundamentally about change, but it’s also about fuzziness and questions that harry our concepts of essentialism.