This post is a collaboration- I did the bulk of the typing, but the ideas and sourcing were the product of a long and rather frantic e-mail exchange with Steve Bodio, who has pictures, additional comments, and some explication of politics affecting the falconry issues here: Big Black Nemesis
In the last post in this kind-of-a-series, I talked about species concept and how biologists go about attempting to define what a species actually is so that they can organize phylogenetic trees and generally go about the process of fitting things into discrete categories that seems to be so central to human understanding. I tried to explicitly point out the major weaknesses of each, but only hinted at the major flaw in biological species concept, because that flaw was rather unexpected, still not conventional wisdom with regards to species and speciation, but undeniably there and leading to Interesting Problems.
As I said, an implicit assumption contained within biological species concept is that it assumes that different species are very genetically distinct from one another and that their cladistic history and points of branching may be accurately measured by the degree to which they are genetically distinct. The idea in general was established well before it was possible to map entire genomes and compare them to one another, but there seemed to be nothing wrong whatsoever with the principle.
Where the problem came in was that once this sort of systematic mapping and comparing began to happen, a disturbing number of groups containing members that were very clearly different species in the morphological and ecological models, even ones that were presumed to be completely reproductively isolated from one another… were not all that genetically distinct at all, or were not genetically distinct in ways that matched their known patterns of distribution or history as a species. It seemed the morphological and ecological species-concept people had a very sound point all along- it turns out that what makes an organism special as a distinct entity in and of itself, in ways relevant to categorizing, cannot be read directly from its genes. This was a troubling thought-especially since it slaps a big question mark on the accuracy of phylogenies derived from tracking the degree of divergence of “stable” single point genes or mitochondrial DNA, which although much more stable than those portions of the genome more subject to direct selective pressure apparently may vary much more in speed of mutation than assumed- but it wasn’t really a devastating blow to species concept as defined by reproductive isolation, just one of the things assumed to be a direct consequence.
What IS a troubling idea for biological species concept is the idea that reproductive isolation between species that are very definitely different species may not necessarily be nearly as firm as thought unless the isolation imposed was of a firm geographical or mechanical nature.
Speaking of wolves as I was last week, let’s talk about them. We know that wolves and dogs are interfertile like most if not all Canids, and that hybrids betwixt the two are generally only ever either the product of deliberate human creation or a fringe area of habitat for wolves in which a wolf and a dog might each be desperate enough for company and mates to deal with dogs on terms other than the completely adversarial one that is normal operation for them. There may be some humans confused on the point, but wolves and dogs know they are different species; they treat one another either as competing predators or, in the case of smaller dogs, the wolf is the predator and the dog is the prey. This is not a very disturbing idea for human taxonomists because it is broadly assumed that the dog is immediately derived from some strain or another of Eurasian-born gray wolf, C. lupus, and therefore if sometimes lines gets crossed, well, speciation takes a long time to fully complete and sex is a strong drive.
Where the case of wolves really gets interesting is that, speaking of species in which a DNA sample won’t tell you what it is, in terms of a bottle of wild New World canid blood you’ll have more reliable results asking the sampler who drew it whether it came from a wolf or a coyote (C. latrans) than you will running the sample, as Raymond Coppinger has famously ranted. Why this is so interesting is the respective evolutionary histories of lupus and latrans: grey wolves evolved, to the best of everyone’s knowledge, in Eurasia. They are an Old World predator who migrated into North America across the Bering Land Bridge during its periods of existence, possibly in successive waves. Coyotes, in contrast, are a New World canine that survived the Ice Age collapse that devastated so many North American species to howl in a new epoch and a new ecology. Their most recent common ancestor dates back to the Miocene.
Things get worse when the red wolf, C. rufus, is added into the picture: since the advent of genome analysis, it’s coming into serious question whether or not the red wolves are a distinct species from wolves and coyotes, impossibly “polluted” with coyote genes, or are simply now a very large hybrid zone between wolves and coyotes. What is known for sure is that what genes they have that they don’t share with coyotes, they do share with wolves, and what genes they don’t share with wolves, they do share with coyotes. Hybridization with coyotes was always a concern for red wolf conservation*, when it was feared the population would simply become coyotes- now the question is whether the existing “red wolf” population was created in the last century out of the remnants of the original red wolves plus coyote blood as they collapsed under habitat pressure, whether they were an older hybrid population created from a similar collapse under habitat pressure from eastern Native Americans, or whether “C. rufus” has always simply been a very large hybrid zone between grey wolves and coyotes.
The red wolf, whatever it may truly be, is not alone in its status as a potential hybrid zone “species”; it appears that the northeastern coyote- big, heavy coyotes- and the eastern Canadian wolf are both of rather mingled blood**. Go far enough north and east from the US, and the coyotes get awfully wolflike in both appearance, behavior, and DNA- and go far enough south and east from Alaska, and the wolves get smaller and more coyotelike in appearance, behavior, and DNA. When it comes to answering the question “what is it”, you might as well follow a morphological or ecological concept, because the genes aren’t going to tell you much useful and the reproductive isolation is questionable at best, although coyotes and wolves are dedicated enemies in other areas their habitats overlap- one of the first things the reintroduced Yellowstone wolves did was start killing coyotes as often as they could catch them.
We will return to our New World canines, but for now let’s digress to Old World falcons. The hierofalco group is a monophyletic (all related to each other and with no descendants outside the group) clade of big, level-flying falcons who all inhabit Asia, but between them also cover Europe, Africa, and North America. Their largest and most famous representative is the Gyrfalcon, a big, burly creature by falcon standards that is most at home in tundra, taiga, and rocky cliff areas. It inhabits a belt of territory around the top of the globe. The Saker falcon is a somewhat smaller bird (though still a damn big falcon) that inhabits a band south of the Gyrfalcon’s territory in Europe and Asia, and has a broad northern range of overlap with the southern edge of the Gyrfalcon’s range. Sakers prefer open grassland and lighter forest, though they share a fondness for cliffside residency with their more macho Gyrfalcon cousins. The Lanner and Lugger falcons are the other two members of hierofalco, but are far less germane to the topic of this post, so beyond acknowledging their existence as the two southern representatives we will go no further with them.
Gyrfalcons and Saker falcons are, like wolves and coyotes, completely interfertile- the results of a mating between the two (which need not involve artificial insemination, Gyrs and Sakers will happily form a natural pair) is completely fertile itself and suffers none of the identity crises that make some other avian hybrids significantly less adapted than their parents. And as the reader might expect who has been following me so far, all broad genetic analysis of Gyrfalcons and Saker falcons shows the evidence of a high degree of hybridization between the two populations, even when it is taken into account that their own isolation was much more recent than the canids’.
This is the point at which things get a bit political. There is a region Steve Bodio refers to as the “Four Corners” in Central Asia, overlapping Kazakhstan, Siberia, and Mongolia, in the northern end of Saker territory and the southern edge of Gyrfalcon territory, in which the Sakers get awfully Gyrlike. Falconers in Central Asia call them Altai falcons and consider them desirable for their greater hardiness over the Gyrfalcon*** and greater size and power over the Saker. What makes it more problematic is that Arabic falconers agree, and have built up quite a classification system of Altai “types”, some of which they are willing to pay quite highly for, which naturally disturbs some conservationists, who have had distinctly negative experiences with rich men willing to pay highly for wild animals, whole or piece by piece. In terms of size and color morphs, the described Altai varieties are indistinguishable from deliberately produced Gyr/Saker hybrids.
Although there is broad acknowledgment that the genetic studies of Gyrfalcons and Sakers shows a high degree of hybridization both past and ongoing, there is a fair amount of argument about what this means. Right now one proposed theory is that the hybridization mostly comes from deliberate Gyr/Saker hybrids created by falconers and then escaped back into the wild, with possibly some natural habitat pressures coming from humans also driving the sort of natural hybridization caused by dwindling populations desperate for mates.****
This is the point at which I stop describing things that everybody agrees on- widespread genetic evidence indicating hybridization, with its almost certainly being entirely natural hybridization in one of my two examples- and put on my pith helmet and butterfly net in pursuit of the Wild Speculation. Tally-ho!
Earlier we discussed parthenogenesis, where it shows up, and how it originates, and joined in some speculation as to how it may be an evolutionary strategy for species colonizing new and inhospitable habitats to fix a highly adapted line and allow for rapid radiation. In that post hybridization, associated as the instigating event of most vertebrate parthenogenetic lines, played a role as a way to experiment with several radical new combinations of genes not present in the parent species, with any that were markedly more successful being the winners to move into the new habitat.
One of the things the Four Corners region of Central Asia and North America in general share in common is that they are both extremely diverse regions that have experienced repeated and often violent environmental change. In North America, glaciers have swept in and out and carved mountains, valleys and rivers, instigated massive floods, and left new open plains in their wake. In Central Asia, the retreat of the ice caused a band of taiga forest to spring up where there had been tundra- now prime Saker habitat- but in the Four Corners region, the separation was incomplete; it has everything from cliffy mountains to tundra to taiga to grassy valleys to bog, sometimes only miles from each other.
North America was also affected much more dramatically by another potent agent of change: humanity. The first Americans wandered over the Bering bridge along with the wolves, caribou/elk, and brown bears, and they tended to leave nothing they touched unchanged. They chased some species out of existence, encouraged others, and created a great deal of grassland where there had been forest, including the regions representing modern red wolf territory, which were greatly affected by slash-and-burn agriculture*****. Of more recent effects of humans, I need say relatively little- extirpation of predators was regarded as a universal benefit in America until quite recently, and forest, grassland, swampland, and desert have wandered rapidly in some places.
Evolution is the process of change over time, and in the case of repeated and dramatic environmental change and disturbance, time is short and the creature that can change quickly has advantage. Humans are a particularly polarizing force of change for North American canids, because an outbreak of humans in a given area is something that is always a very bad thing for grey wolves but often a net benefit to coyotes. Humans will chase and try to eradicate both, but while the pack-dependent wolves almost always buckle to the pressure and are driven back, the coyotes simply splinter their groups into pairs and dramatically increase their breeding rate. Wolves cannot urbanize; coyotes are adept urbanizers. A coyote’s real problem in the wild is other predators, including wolves- mountain lions and wolves are much better at killing coyotes than humans are, but humans are much better at killing those other predators than they are at killing coyotes in a way that sticks.
Canines are unusually plastic in their genetics; relative to other mammalian groups, a canid can adjust its size and proportions quite quickly in response to new conditions. It was already widely observed of the coyotes that had radiated east, particularly the northeastern ones, that they were much bigger than most western coyotes. That they were wolflike in their genetics was a surprise, but that they were wolflike in their hunting seemed simple ecological sense; with the eradication of nearly all large predators from the east, deer grew so numerous multiple states have been forced to treat them like vermin. “Normal” coyotes are already known to be able to pack up and take deer, but with deer representing a rich and untapped food source, immediate pressure would favor bigger, stronger coyotes better adapted to taking deer for the bulk of their meals rather than rabbits and rodents. Coyotes that were, in fact, more wolflike.
We know from the reports of colonists that there were wolves in Eastern Canada and New England when they got there, and we know from similar sources that there were red wolves in the southeastern US when they got there, but a colonist is forced to rely on morphological species concept: if it is physically, ecologically, and behaviorally wolf-shaped, then it’s a wolf, and will be reported as such. We can analyze the DNA from old skins in natural history museums, and this has been done with the red wolf (no difference from the modern, “hybridized” red wolf), but no such specimens exist that predate the effects of European colonization in North America.
The current generally accepted picture of hybridized and “polluted” red wolves and northeastern coywolves and coyote-hybrid eastern Canadian wolves is that they all represent an unnatural condition born of coyotes radiating into old grey and red wolf territory and the desperate survivors hybridizing with the newcomers. What I am suggesting is that this is may actually be a very old strategy for the New World canines, born of constant and rapid change: the red wolves may have always been thus, and likewise the Eastern wolves. We know that the coywolves are very well adapted, rather than being some sort of damaged hybrid “compromise” between the parent species- their numbers grow despite their pressures and the fact that they are not protected.
Where coyote and wolf populations and niches are healthy and well-defined, they are competing predators, enemies, and behave as such… but perhaps when local conditions make it so that one niche and population is being dramatically cut back, hybridization- in a sense, the genetic line changing teams- becomes appealing. This is already a version of what’s already believed for how hybridization between the species became so common, the only new thing I’m suggesting is that this may have been a winning strategy for both species in the face of pressure and change for much longer than modern human populations have been here. When things change and get bad for one species, or opportunity is simply knocking- the most rapidly adaptive route may be to flow into the other.
For the falcons, the story is a bit more stable. The Altai falcons may represent a similar case of adaptive hybridization, or they may represent a case of incomplete speciation in which the middle zone of their shared territory offers so many different kinds of niches that there is simply no force driving them to completely split- or rather, too many forces acting at once in different directions. It is also possible that the sheer variety of the region in which hybridization seems to occur- and maybe very often and completely naturally, falconers certainly need exert no effort to get Gyrfalcons and Saker falcons to treat one another as appealing mates- means that there are several micro-niches that varying combinations of Gyrfalcon and Saker falcon morphology and behavior would be ideal to exploit, which would create not only positive pressure to hybridize, but also suggest an evolutionary reason for why different but consistent-over-time varieties of “Altai Falcon” persist.
The classic picture of speciation that most of us learn is that groups of animals become separate species when things change enough in some way that distinct but stable evolutionary strategies emerge, and whether because of geographic separation or other kinds of isolation, over time the groups split into two different species based around the two distinct strategies. Natural hybridization violates this model, because in theory the result would be something imperfectly adapted to either niche and, if the parent species had the poor taste to mate in the first place, the result would have no significant impact on the evolutionary history of either species.
But when the environment refuses to stop changing, strategies in consequence cannot remain stable, and children that are much different from you stand an even chance of being better off… perhaps it pays to hold your neighbors close.
*Conservation has always been a tremendous pressure force in sorting animal populations into clear species, because you need a species definition to qualify for protection. The controversy in red wolf conservation is that, in the lights of the conservationists, whether they are red wolves or “just” hybrids of species with healthy populations of their own means the difference in protection versus no protection.
**If you read the article, you’ll see that the wolf researcher studying these overlapping gene pools proposes that coyotes are only about 300,000 years old and spawned from a northern wolf ancestor in Canada, and if you’re following your chain of implications suggests that the red wolf is ancestral to both the Eurasian grey wolf line and coyotes. This clears up the disturbing natural hybridization implications, but also disagrees quite dramatically with the paleontologists, who hold that the coyote is the oldest of the surviving distinct species of canid in North America. To be fair to everyone, canid taxonomy is a messy and incestous business, as we are seeing.
***For all their toughness versus ice and snow, Gyrfalcons tend to have lousy immune systems and get sick at the drop of a hat in captivity. Warmer regions tend to breed more and more virulent bugs than Arctic ones.
****Bear in mind that the Four Corners region, while providing many appealing residences for large falcons, is highly inhospitable to humans. It is very sparsely populated and most Western scientists aren’t in a massive rush to get out there and start counting heads, so a picture of the actual falcon population of all species and varieties in between is very foggy.
*****They left this part out of Pocahontas. The European memory of vast, intimidating forest primeval being the condition of the American seaboard is not so much the state it was in when they arrived as it was the state it was in after imported European pathogens killed off most of the tribes that had been there, their farms with them. Forests can be quite quick to retake that territory once it is again unoccupied- New England’s reforesting post the Industrial Revolution is a case in point. The topic of whether the extent of the South American rainforest represents an always-was condition or a condition acquired after the South American disease-induced native die-off is one that causes much bristling of beards as well.