When asked to consider the impact that humanity is having on the planet and its fauna and flora, it would be surprising if most people didn’t mention extinction. After all, we are constantly asked to donate money towards saving charismatic, cuddly species such as pandas or mountain gorillas (I wouldn’t recommend attempting to cuddle either), and it’s no secret that the planet is now facing its sixth mass extinction in its long history.
This one is different to the other five, in that species are not disappearing en masse due to a natural disaster (such as K-Pg) or a sudden, radical shift in climate (the ice age), but because of the impact of a single species: humans. This made headlines recently when scientists declared an end to the Holocene geological epoch, ruling that human impact has now altered the planet and the climate so much that it deserves recognition, and coining our new epoch, the Anthropocene.
But perhaps our legacy is more complicated than it would appear. After all, if we have changed the world enough to warrant geological recognition, maybe we are doing more than just wiping out species. This particular aspect of this brave, new, anthropocentric world is becoming increasingly apparent in North America, where wolves and coyotes have begun to occupy more of the same habitat. Obviously, in the animal world, there’s very little recognition of the superficial boundaries between countries, so animals such as wolves can move rather freely between the no-touching zone that marks the USA/Canada border. This, coupled with the increasing urbanisation of our wilderness, has started to force these once-distinct populations of wolf and coyotes together and led to species hybridisation.
There are plenty of examples of species hybridisation. I imagine the first to come to mind for most people are mules (a horse/donkey hybrid), or a liger (a lion/tiger hybrid), but most wild hybrids are inconsequential due to being infertile. This is where the wolf/coyote hybrids are different: they are fertile, and they are breeding.
What’s more, these hybrids (named coywolves) have a trait known as “hybrid vigour”, where they adopt the best traits from both parent species. Like most canids, they work well in family groups and hunt in packs, but their smaller size means that they don’t have to rely on the enormous prey (such as bison) that wolves tackle. Furthermore, their smaller size and more sociable instincts also make them adept at integrating into urban environments, widening their habitat range and giving them the chance to get food without hunting at all.
This is very much a special case, though not an isolated one. We ourselves are a hodgepodge of Homo sapiens and Neanderthal, with a smattering of other hominids thrown in for good measure, and we are arguably the most successful species to have lived.
So, while species hybridisation happens more often than one might think (both in and out of the laboratory), the production of fertile offspring from such encounters is rare, and hybrids with better prospects than either of their parent species is even rarer.
The reason why coywolves are fertile is because their parent species are very closely related. Recent genetic studies have shown that modern dogs and wolves share a common ancestor from approximately 27,000 years ago, before they diverged to form modern wolves and domestic dogs. This is much later than previous estimates. It seems that gene flow between “distinct” species of canids has continued, meaning that they can produce fertile offspring should they hybridise. So, just as you can create crossbreed dogs, it would seem that you can do the same with other canids. In fact, a recent genetic study has shown that the red wolf (Canis rufus) has been a coywolf all along despite being deemed a species in its own right.
So what does this mean for our understanding of species and our impact on biodiversity? Despite species hybridisation being a relatively familiar concept in zoology, it does pose an important question in terms of how we conserve and maximise the planet’s biodiversity in the light of climate change. After all, conservation funding only goes so far and many conservationists wouldn’t be blamed for wanting to stick to a “purist” approach of conserving the parent species, not the hybrid.
However, it’s not always as simple as that: the red wolf is considered critically endangered by the IUCN red list, and if the purpose of conservation is to maximise biodiversity, shouldn’t hybrid populations be included too? Or does this blur the lines between “true species” and “nonspecies” too much?
It’s not just a conservation question either: such hybridisation has also been noted in North American rattlesnakes, resulting in a hybrid with a completely new venom, which needs a completely new anti-venom to treat bites. If we are unable to recognise this biodiversity adequately, we cannot react to these changes, and that could negatively impact both humans and the animals we’re trying to protect and conserve.
Whatever the answer, it’s one that needs to be addressed soon if species hybridisation is set to be part of our legacy on this planet. Our population growth is reducing the habitats for these animals and increasing our interactions with them, whether they are urban coywolves or rattlesnake hybrids. The Anthropocene isn’t just changing the climate, it is changing how animals interact with each other and although it’s incredibly exciting, we need to be sure we do what we can to understand what our impact on them is.