An F1 cross between a gray wolf and a coyote that was produced through artificial insemination.
A few months ago, I wrote about a discovery that two species of howler monkey have evolved greater genetic divergence in a hybridization zone in southern Mexico. The hybrids were less fit to survive or reproduce, so natural selection has favored those individuals in both species that were genetically more divergent where their ranges overlap. This phenomenon, known as “reinforcement,” is a powerful tool that maintains both species as distinct.
I have been thinking about how this phenomenon may have played out in wolf evolution in North America. We have found that gray wolves across North America have at least some amount of coyote introgression, which has been revealed in several full genome comparisons.
The wolves that have most evidence of coyote introgression are those that live in areas that were not in the historic range of coyotes, while those with the least coyote introgression tend to be in the areas where gray wolves and coyotes were sympatric.
It is possible that something like reinforcement went on with wolves and coyotes living in the West. Hybrids between gray wolves and coyotes were probably less likely to be able to bring down large prey or were too large to live on small game, which is the staple diet of most Western coyotes. Over time, reinforcement through natural selection could have caused greater genetic differences between Western wolves and coyotes, and Eastern wolves were without coyote and thus never developed these greater genetic differences.
When coyotes came into the East, they mated with relict wolves, so that we now have whole populations of wolf with significant coyote ancestry.
Now, this idea is not one that I find entirely convincing. One is that ancient mitochrondrial DNA analysis from wolves in the East suggests they had coyote-like MtDNA, which, of course, leads to the idea that the wolves of the East were a distinct species.
Further, the discovery of the recent origins of the coyote makes all of this much more murky. Again, reinforcement is a process that is only just now being sussed out in the literature, and gray wolves and coyotes are unique in how much introgression exists between them. Their hybridization has essentially been documented across a continent. The only wolves that have no evidence of coyote ancestry live on the Queen Elizabeth Islands of the Canadian arctic. No coyotes have ever lived on these islands, so they have never introgressed into the wolf population.
The howler monkeys in the reinforcement study hybridize only along a narrow zone in the Mexican state of Tabasco. They are also much more genetically distinct than wolves and coyotes are. The monkeys diverged 3 million years ago, but the current estimate of when gray wolves and coyotes shared a common ancestor is around 50,000 years ago.
So gray wolf and coyote “speciation” is a lot more complex than the issues surrounding these monkeys.
But reinforcement is something to think about, even if it doesn’t fit the paradigm exactly.
