Natural History

We know that hybridization is a big thing in the genus Canis.  Indeed, scientists are still debating about the validity of certain species because some of the extant forms of wolf could very well be hybrids between gray wolves and closely related species. Everyone thinks that the large coyotes we see in the East are all coywolves, even though they don’t have that much wolf ancestry. but then we have very good genomic data that shows that coyotes and gray wolves really aren’t that different genetically.  We know that Ethiopian wolves were threatened with and still could be threatened with hybridization from domestic dogs, but we also know that getting dog genes into a wild canid isn’t always a bad thing. Wild gray wolves in North America got their black color variant from a single Pre-Columbian black dog that crossed into the population between 1,500 and 7,250 years ago in the Yukon or the Northwest Territories.

I have often wondered if we could detect hybridization that went on long before all these wolf-like canids truly diverged, and a recent paper in The Journal Cell reveals that hybridization has always been a feature of these wolf-like canids. Gopalakrishnan et al. compared the genomes of gray wolves, coyotes, domestic dogs, golden jackals, the African golden wolf, the Ethiopian wolf, the dhole, and the African wild dog to see if there was any evidence of hybridization in the lineages.

The authors found that the African golden wolf was actually a hybrid species that developed from gene flow between the gray wolf and the Ethiopian wolf, which likely had a much more extensive range in Africa than it does now.  The authors also found that the clade (which I think is actually a single species) that includes the dog, wolf, and coyote received genes from an unknown species of canid. The dhole and African wild dog have also hybridized in the past, probably because both the dhole and African wild dog once had ranges that overlapped in the Middle East or in North Africa.

The discovery of this unknown species is perhaps the most intriguing. The authors speculate that it might have been the dire wolf or the extinct North American dhole, but seeing that this species fairly close to the division between the dhole and African wild dog, I think a more likely candidate is Xenocyon lycaonoides.  This animal has been posited as an ancestor the dhole and the African wild dog, but a more convincing argument is that the African wild dog derived from Lycaon sekowei.  It is not clear yet what the dhole derives from, but it could have derived from Xenocyon or shared a common ancestor with it.

Xenocyon was the dominant wolf-like canid in Eurasia and Africa during the early part of the Pleistocene, but by the mid-Pleistocene, it began to become less common, and as its numbers dwindled, the diminutive wolf, Canis mosbachensis, began to fill its niche, eventually evolving into the modern gray wolf, which also led to the coyote and domestic dog lineages, as well as the hybrid African golden wolf.

Maybe, as the Xenocyon’s numbers dwindled, a few remaining ones hybridized with C. mosbachensis, perhaps introducing some genes from better pack cooperation and larger size that helped the smaller wolf fill the bigger canid’s niche.

The authors are clear that we need lots of ancient DNA from these extinct canids before we can engage in flights of speculative fancy, but seeing that this unknown canid was so close to the dhole, I think that this animal is a better place to look. Xenocyon might be a bit too old to find viable DNA in fossil remains, but it is certainly possible that we could find some.

So yes, hybridization has greatly affected the evolution of wolf-like canids in the modern era, but hybridization always has. Similar findings have been discovered in bears and various members of the cat family.  My guess is that virtually every clade will have had some of this going on, even if the current species do not hybridize.  Speciation happens, but chemical interfertility isn’t lost for quite some time after speciation. Gene flow continues on with related species, which continues to affect their evolution.

Yeah, evolution is a tangled bush that also has vines that reach out and grab adjacent and not so adjacent twigs.