Mike the Mad Biologist

One of the reasons I’ve learned to stay away from debates about “what is a species” is that practical species definitions (i.e., something we can use to classify critters) do a lousy job of describing the process of speciation, while conceptually sound species definitions (ones that describe the speciation process) are usually miserable when you actually try to classify organisms. Why? Because delineating species implies (and requires) sharp biological breaks that might not exist. Case in point, the Eastern coyote:

Two separate teams of researchers studying the genes of coyotes in the Northeast reported evidence that these animals that have for decades upon decades been thought of as coyotes are in fact coyote-wolf hybrids….

Both teams found that the animals carry wolf and coyote DNA. The paper by Dr. Kays and his colleagues was published in Biology Letters; the paper by Dr. Way and his colleagues was published in Northeastern Naturalist.

Based on the wolf DNA found in the Eastern coyotes, Dr. Kays and colleagues hypothesize in their paper that Western coyotes dispersing eastward north of the Great Lakes across Canada during the last century mated with wolves along the way, bringing that wolf DNA along with them to the Northeast.

The findings may explain why coyotes in the East are generally larger than their Western counterparts — that is, more wolflike in size — and why they are so much more varied in coat color, as might be expected from a creature with a more diverse genome. It may also explain why Eastern coyotes appear to be more adept as deer hunters than their Western forebears, which tend toward smaller prey, like voles and rabbits.

What the finding does not settle is how to define exactly what these animals are, or for that matter, what to call them. Dr. Way favors the term “coywolf” to denote the animals’ hybrid heritage. He said because these animals are part wolf — species that enjoy protected status — they deserve some benefits not available to coyotes, which are typically freely hunted.

Dr. Kays, however, says that he is not a fan of the name, in part because the animals are “mostly coyote and a little bit of wolf,” but also because the Eastern coyote may be less a finished product deserving of a name and more an evolutionary work in progress….

One major complication is that all the species in the genus Canis, to which the coyote belongs, can successfully interbreed. In other words, coyotes (or Canis latrans, meaning “barking dog”) and domestic dogs (Canis familiaris) and every kind of wolf, from the red wolf to the Eastern wolf to the gray wolf (Canis lupus), can mate and produce perfectly healthy pups. No wonder, then, that interactions among these species have led to a genetic mess that researchers sometimes refer to as “Canis soupus.”

I do think coyotes are amazing creatures, even if they are Canis soupus.

Comments

#1 MattK
October 1, 2010

Interestingly, in Algonquin Park Ontario, most of the Canis are fairly pure Eastern Wolf (C. lycaon) but outside of the park they are mostly Coyote (C. latrans) with a few being mostly Eastern Wolf. There is research going on now to determine how gene flow is being limited in the absence of physical barriers. The primary hypothesis is that the park wolves are able to maintain an intact pack structure much more often whereas outside the park anthropogenic mortality and habitat fragmentation lead to a much less stable pack structure and more hybridization.

In contrast to the eastern situation, in western North America there is basically no hybridization between Wolves and Coyotes. In the west and north the wolves are Canis lupus (Grey Wolf) which is the bigger ‘classic’ Wolf. My understanding (and this may be somewhat outdated now) is that the some of the ancestors of Wolves and Coyotes diverged when some colonized Europe and Asia via the Bering land bridge. Those became the Grey Wolf. In North America they diverged into several species including the now extinct Dire Wolf, Coyotes, and Eastern (including Red) Wolves. Grey Wolves reinvaded North America some time afterwards. After European colonization, Eastern Wolves were displaced from most of Eastern North America and the landscape was transformed by forestry and agriculture which allowed Coyotes to expand their range eastward over the last 150 years or so (they only reached the maritime provinces in the last several decades). As they came there was some mixing with remnant Eastern Wolves as well as selection to exploit the now vacant niche for preying on ungulates.
#2 Russell
October 1, 2010

And where does the chupacabra fit into the taxonomy?
#3 NewEnglandBob
October 1, 2010

It seems that all wolves/coyotes/dogs should be one species and be referred to as either sub-species or races. If they diverge genetically and no longer can interbreed then they will become separate species. It is all just naming (I know, there have been verbal wars fought about “just naming”).
#4 MattK
October 1, 2010

The criterion of “can no longer interbreed” has never been a working species definition in biology although when this is true, the groups are definitely different species. The preferred working definition simply stipulates that gene flow/genetic introgression is reduced sufficiently under natural conditions that it is likely that the two populations are under separate evolutionary trajectories.
#5 Mokele
October 1, 2010

You think that’s weird, I’m familiar with at least 4 cross-genus snake hybrids, 2 of which are known to be fertile, and all of which have separations of > 10 million years (in one case, > 90 million years).

“Jungle corn snakes” (Lampropeltis x Elaphe) and “Turbo corn snakes” (Pituophis x Elaphe) are fertile when back-crossed (no info about dual hybrid pairings) and have been separate since at least 10 million years ago (based on both DNA and fossils). I’ve also seen a single (accidental) cross between a pygmy rattlesnake (Sistrurus) and a western diamondback (Crotalus).

By far the weirdest is a hybrid between a woma (Aspidites, a primitive python from Australia) and a ball python (Python, from Africa). These two are massively morphologically and ecologically different, and seem to have been separated since Australia broke off from the rest of Gondwana, yet they hybridize just fine. No idea about fertility, but I know one large breeder has been working with this pairing for several years, so the fact that they haven’t given up means they might have something.
#6 MattK
October 1, 2010

I’ve heard about some of the snake ones. Some turtles are like that too – Blandings Turtles and Wood Turtles for example have been hybridized even though their habits, habitat, and appearance are nothing alike. Even their sex determining mechanisms (one nest temperature, the other genetic) are different. They are also in separate genera. Toads too (e.g. here. Lions and Jaguars can also interbreed, as can Ocelots and Cougars apparently.
#7 Kevin
October 1, 2010

but also because the Eastern coyote may be less a finished product deserving of a name and more an evolutionary work in progress….

Um… isn’t every living thing an “evolutionary work in progress?” If we only named “finished products,” we could only ever name things that are extinct.
#8 darwinsdog
October 1, 2010

There are at least twenty different species concepts or definition and each has its own particular sphere of applicability. Ernst Mayr’s “Biological Species Concept,” which emphasizes reproductive isolation, is only one such definition. Defining “species” is particularly problematic with clonal organisms. It’s often said that the species is the only non-arbitrary taxonomic category but I dispute this. To my mind the species is every bit as arbitrary a construct as the genus, family, etc. Darwin was closest to the mark (as usual) when he said something to the effect that the species is whatever the person most familiar with the group in question says it is.
#9 Rob Jase
October 1, 2010

A quick step away from coyotes but hopefully still on subject, I’ve thought for some time that the onza, a supposed crytid that is genetically the same as a puma (as per specimens) but is built more like a cheetah, might just be another example of potential speciation in action.

Any thoughts?
#10 chris Holte
October 2, 2010

The use of the word “species” for populations that can interbreed but choose not to, reflects prejudices and irrational behavior among the scientists more than anything about wolves and coyotes. Certainly the definition of a species as two populations that can’t interbreed would make Canis not a “Genus” but a species, and the members of Canis populations and sub-species not separate species.

That might bother some scientists but would at least restore some semblance of sanity to their arguments. Certainly nature is not static, most durable species are a “work in progress”, and scientists need to value and understand diversity not get confused by it.

If we are to survive we need to recognize that adaptability, diversity, and balance are important in nature, not just for their own sakes, but for ours. Wolves survive in preserves because they and humans have niches that overlap and thus conflict. [They eat domesticated animals and pets, and if they get too familiar they attack humans]. Coyotes survive among humans because they fit themselves into niches that avoid competing with humans. It is really that simple.
#11 Al Sutlick
October 2, 2010

Actually, this really isn’t new information. Dr. Phil Gipson, now at Texas Tech, presented extensive work on Wolf-Coyote-Dog hybridization back when I was a wildlife student 35 years ago. Very graphic when you started looking at “typical” skull size at both ends and he started filling in between with Coyotes and Red Wolf from different parts of the country
#12 MattK
October 4, 2010

The use of the word “species” for populations that can interbreed but choose not to, reflects prejudices and irrational behavior among the scientists

No it doesn’t. You are obviously not familiar with the concept of prezygotic isolating mechanisms. Prezygotic isolation has been an important and widely acknowledged aspect of every species concept that has ever been in wide usage (outside of paleontology where it is not applicable) since Mayr proposed the biological species concept. You seek to define ‘species’ in a way that is totally disconnected from the reality in nature. Your definition does even simplify the situation. ‘Species’ would still be an artificial classification imposed on natural systems to help us organize our understanding of it. The ‘cut off’ would still be arbitrary. Shall species that have been classified in different genera but have been demonstrated on one or two occasions to interbreed be lumped together as one? What about if they have only interbred in captivity? Can we ever be sure that it hasn’t happened occasionally in the wild? Are lions and jaguars really the same species? The difference with your system is that you would obliterate from the taxonomy legitimate understanding of the diversity of populations and their probable relative evolutionary trajectories. What good does that do? How does that make the system more usable, more informative, or more reflective of the underlying natural processes? How does it help us describe and catalogue biodiversity?
#13 ross
October 4, 2010

>And where does the chupacabra fit into the taxonomy?

Wolves crossed with Republicans
#14 d
October 4, 2010

You seek to define ‘species’ in a way that is totally disconnected from the reality in nature.

However one decides to define ‘species’ it will be more or less disconnected from the reality of nature, since such a decision is based on arbitrary criteria to which many exceptions occur. All of the many species definitions break down when considered in ways they were never intended to cover. For instance, I could contend that by Mayr’s biological species concept my grandmother and I belong to different species since we are absolutely reproductively isolated. (She had undergone menopause before I was born.) Likewise, species definitions devised for sexually reproducing organisms are essentially meaningless if applied to clonal organisms.

Shall species that have been classified in different genera but have been demonstrated on one or two occasions to interbreed be lumped together as one? What about if they have only interbred in captivity? Can we ever be sure that it hasn’t happened occasionally in the wild? Are lions and jaguars really the same species?

Sure, why not? So long as doing so helps us organize our understanding of natural systems by imposing an artificial classification on them, as you contend. You may not agree that Chris’ system helps us organize our understanding but that may only be because you don’t think in the same terms he does.

The difference with your system is that you would obliterate from the taxonomy legitimate understanding of the diversity of populations and their probable relative evolutionary trajectories.

What is known about the diversity of populations and their probable evolutionary trajectories is independent of what one decides to call such populations.
#15 MattK
October 4, 2010

I could contend that by Mayr’s biological species concept my grandmother and I belong to different species since we are absolutely reproductively isolated.

Are you being deliberately obtuse?

What is known about the diversity of populations and their probable evolutionary trajectories is independent of what one decides to call such populations.

No it is not. That is the whole damned point.

…Sure, why not? So long as doing so helps us organize our understanding of natural systems by imposing an artificial classification on them, as you contend.

But a genus level species concept would decrease our understanding and would still be totally pointless and no more intellectually pure (barf). And besides that, if you want to throw out the entire underpinning of taxonomy (which is itself the underpinning of all the other scientific endeavors that examine the diversity of life) then you ought to have a better reason than ‘why not’.

I think the problem with maximal reproductive isolation fanatics is that they have no real world experience with species in the wild. They do not understand how a rational species concept based on rates of gene exchange is useful for cataloguing our understanding of wild populations because they have no understanding to catalogue.
#16 darwinsdog
October 4, 2010

I could contend that by Mayr’s biological species concept my grandmother and I belong to different species since we are absolutely reproductively isolated.

Are you being deliberately obtuse?

No, I am making a point about the arbitrariness of any and all species definitions.

What is known about the diversity of populations and their probable evolutionary trajectories is independent of what one decides to call such populations.

No it is not. That is the whole damned point.

So if people didn’t name or categorize these populations nothing could be known about their diversity and their probable evolutionary trajectories? I have suggested before that taxonomical categories be given numerical denominations and that names (in Latin or any other language) be dispensed with. So far, this suggestion hasn’t taken hold. You seem to be saying that the name is the thing, or the menu the meal, map the territory, etc. But okay, I don’t really care, so long as taxonomy accurately reflects phylogenetic relationships. Doesn’t matter one whit to me if Canis is regarded as being a genus or a species.
#17 Art Souther
October 10, 2010

MattK,

I’m trying to track down the time frame of the evolutionary splitting of wolves and coyotes and am hoping you might be able to point me to some good references. This notion of separate evolutionary trajectories is intriguing, as it should have something important to say about the generalization < -> specialization continuum and extinction.

I also would appreciate any refs you have regarding the Algonquin example you cited.
#18 Jim Thomerson
October 11, 2010

We taxonomists try to understand what is going on in nature, and recognize, identify, describe taxa in such a way as to express what we know and improve our understanding. I don’t think there is a Procrustean species definition which is universally the most informative. Nor is there a single universal speciation process. All kinds of things can happen with species capable of interbreeding come into contact. They may continue their solitary evolutionary pathways, separated by strong prezygotic isolating mechanisms. Maybe there is intensive hybridization, hybrid swamping, which drives one of the two to extinction. Hybrid swarms may persist for periods of time without introgression into either species, etc, etc. Hybridization is fascinating.