Advertisements
Feeds:
Posts
Comments

Archive for April, 2019

hooded vs carrion crow

In Europe, there are crows. The most famous of which is the carrion crow, which looks and behaves quite like the American crow.  It is usually black, fairly omnivorous, and it often regarded as an agricultural pest.

At one point, it was believed that carrion crows existed in two distinct phases, the common all black form, which is common in Western Europe, and the phase that is marked with gray on the neck and body.  This form exists in the northern parts of the British Isles, where it has been called the grey grow, the hoodie crow, or the hooded crow. This form is found in Northern Europe, Central Europe, and the Middle East.

However, ornithologists began to notice that where their ranges overlapped, it was quite unusual to see hooded crows paired off with black carrion crows, but the traditional taxonomy still thought of the hooded and black forms as being distinct phases of the same species.

Because the two forms were rarely seen mating or paired off, it was decided to call the carrion crow and hooded crow distinct species, and this is the current understanding. The hooded crow is Corvus cornix and the carrion crow is Corvus corone. But the two birds are otherwise quite similar in terms of ecology, vocalizations, and general phenotype. All that really separates them is the coloration.

Scientists that surely there was a rather deep genetic divergence between the two species, which is why there is a species barrier between the two forms of similar crow.

However, when the genomes of carrion and hooded crows were sequenced, it was revealed that they were almost identical.

Less than .28 percent of the genome varied.  That variance was related to the fact that carrion crows have gray plumage on their neck and torso.

But that little variance is enough to create a species barrier between the carrion and hooded crows. Birds are highly visual, and when young crows imprint upon their parents, they imprint heavily upon what they see. If a young crow is raised by parents that are gray hooded, they will look for mates that are gray hooded. IF their parents are all black, they will look for mates that are all black.

However, it has also been suggested that these crows look for mates that appear not to have aberrant mutations, and this keeps the crows looking for mates that generally look like those belonging to their general family group and social circle.

Whatever the case, we have two very closely related species that do not hybridize. They probably became distinct during the heavily glaciation cycles of the late Pleistocene. One form evolved a gray hood and one evolved an all-black form. Maybe founder effect is the only real reason for this difference in plumage, for this difference in plumage is awfully random.

But that difference in plumage color is enough to create a species barrier, which, if it holds, will lead to greater and greater speciation between hooded and carrion crows.

This discovery about crows is quite interesting for what it tells us about dog taxonomy. Domestic dogs and wolves live together over a broad swathe of Eurasia, and for many centuries, dogs and wolves were regarded as distinct species. However, we have recently found that there is an extensive gene flow between Eurasian gray wolves and domestic dogs across Eurasia, and this gene flow is so significant that the majority of Eurasian gray wolves are estimated to have some relatively close dog ancestry.

Carrion and hooded crows have a clear species barrier that is likely only going to intensify as the two lineages continue to diverge with very limited gene flow. Dogs and gray wolves are not experiencing such a species barrier. Indeed, it looks like the gene flow between dogs and wolves is only going to increase as wolves move into human-dominated lands in Western Europe, and the Eurasian dog population continues to increase along with the human population.

So here we have two crows that are diverging, and the wild and domestic forms of Canis lupus that are continuing their gene flow.  Closing down gene flow is a major part of speciation, and the crows are clearly on their way.

Advertisements

Read Full Post »

feral horses

I make no bones about my view that the horses that roam the American West are feral and should not be regarded as native wildlife. This view shouldn’t controversial, but it is.

Lots of romanticism exist about horses and the West, including that brief time when Native cultures used horses as their greatest asset in hunting bison.

But the truth is that the horses one might see roaming the ranges of the American West are all derived from domestic horses that went wild on the range. The initial ones were all derived from Iberian/North African horses that Spanish colonizers brought into the New World, but these were later augmented with horses brought over from the rest of Europe.

If one were to say that the various forms of freely breeding swine in North America were feral, it would be easy to get agreement. Suids are not native to the Americas, though a sister lineage, the Tayassuidae, are native to North America. The tayassuids, better known as peccaries or javelinas, once ranged as far north as the Yukon, but since the Pleistocene, they have not ranged north of Texas, New Mexico, and Arizona.  Feral swine, though, exist over large sections of the country, and wildlife and agricultural departments spend lots of time, money, and manpower on controlling their numbers.

Feral horses, though, get special privileges, as do feral donkeys.  They receive a certain amount of protection not afforded to other feral livestock in the Wild and Free-Roaming Horses and Burros Act of 1971. The horses and donkeys are not controlled in the same way feral pigs are. There is no continuous open season on them in the way that most states manage feral pigs.  Indeed, it is actually a crime to kill or harass feral horses or burros on federal land.  Excess horses and burros are managed through roundups, where some of them are deemed adoptable and sold to the general public.

For those of us with a modern ecological mindset, which has a deep disdain for making allowances for feral livestock, this law makes little sense.

But there is a sort of argument for this act. It goes something like this:

The modern horse species evolved in its current form in North America. Some taxonomists contend that there was once a Holarctic distribution of this species during the Pleistocene, and with the latest ancient DNA studies, I tend to agree with this assertion.

The North American population of horses became extirpated at the end of the Pleistocene, and when European horses went feral on the Western ranges, this constitutes a rewilding event.

Now, I don’t buy this argument very much, but I can say that there are some things we might consider. North America’s original population of cougars became extinct at the same time. The cougars that live in North America are derived from South American cougars that recolonized the continent about 2,000 years later.

Further, conservationists and sporting groups spend lots of resources on restoring and protecting elk populations. Elk have a much shorter history on this continent than horses ever did. Different experts have estimated when elk have first arrived. 40,000 years ago has been suggested, but more recent data points to them colonizing North America only 15, 200 years ago.

If elk arrived in North America only that recently, their status as native wildlife exists only as a weird  accident of geography. Elk are the on Cervinae or “plesiometacarpal deer” in the Americas. All the other deer in the Americas are Capreolinae or “telemetacarpal deer.”  Sika, axis, red deer, and fallow deer are also Cervinae, but they were introduced after colonization.

Elk don’t live in far northeast of Russia anymore. The elk of North America are the genetic legacy of this ghost population.

So the feral horse advocates could at least through the recent arrival of elk in North America as something to consider when we say their favorite animal is not native. Horses have a long evolutionary history in North America, and we just happen to be at an odd point of the history of horses that no native horses exist here. The earliest horse, Eohippus, first appeared in North America 52 million years ago.

So the feral horse advocates could say that we have a species that derived from a lineage that was here for over 50 million years that has now been restored through feral livestock and thus deserves these protections.  And this animal has at least as much rights to be free and roaming in North America as a large deer that had no connection to this continent until the latest Pleistocene.

However, the extinction of the horse in North America likely stemmed from natural climate change at the end of the Pleistocene.  Horses became extinct because they were poorly adapted to the new ecosystems, and as we have seen, horses really don’t do that well out in the deserts and semi-arid ranges of the West. They require water tanks to get them through long droughts, and they eat lots of forage. Not as much as domestic cattle, of course, but on ranges that are heavily catered toward livestock grazing, the horses are just an extra set of grazers that are taking away forage from native wildlife.

And even if we were to accept that horses were restored native wildlife, why on earth would we ever extend these protections to donkeys? Donkeys, though of ancient North American origin, evolved in their current form in Africa.

So although I do think of horses as no longer being native to North America, I do think questions of them being native or introduced are complicated, much more so than the question of feral pigs or cats. And yes, there is something like an argument that can be made for the native status of horses, even though I think it’s mostly in error.

Read Full Post »

box turtle

Possibly the greatest debate in all vertebrate taxonomy is classifying the turtle. If you were to ask an expert about where turtles belong, well, it will depend upon the expert and which papers this expert has recently read.

That’s because the literature on turtles is definitely divided. Morphological comparison studies, some of which have used rather complex statistical analysis of characters, have generally placed them closer to Lepidosaurs.  The most common Lepidosaurs are squamates, which are better known as snakes and lizards, and there is another Lepidosaur order with exactly one species left in it. Rhynchocephalia is this order, and it includes exactly one extant species, the tuatara of New Zealand.

Molecular studies have generally placed the turtles either into or close to Archosaurs.  Extant Archosaurs are the crocodilians and birds. All dinosaurs and pterosaurs were also Archosaurs, and birds, which are the only living dinosaurs, are certainly Archosaurs.

One would think that molecular studies would solve this problem, but it really doesn’t.  The problem is that turtles evolve quite slowly, and trying to figure out divergence times based upon mutation rates could result in inaccurate conclusions.

So no one really has a way to resolve this conflict.

And if you were to ask me, I would say, well, I don’t know. We have some ideas, but they are in conflict. And we have no way to resolve them at this time.

But that’s science for ya.

 

 

Read Full Post »

felis lybica

As I have noted many times on this blog, I think that the only way to correctly classify the domestic dog is as form of gray wolf. I am okay with regarding them as a divergent subspecies, but Pierotti and Fogg make a pretty good case that we really cannot define a domestic dog subspecies, because that subspecies would have to include everything from truly feral dogs to pekingese. I think that the wolf genome comparisons also show that creating a special dog or dingo species distorts the monophyly of Canis lupus.

Some will argue with me on this one, but you will have to use a species concept that is totally not based in cladistics or one that allows for a huge amount of gene flow between the two species.  An ecological species concept can work, but then you’re going to be forced to split up Canis lupus into many different species. Arabian wolves are simply aren’t ecologically equivalent to arctic wolves. So I think creating a special dog species is problematic from a systematics perspective.

However, I’ve been asked several times what I think about how to classify the domestic cat. Almost every authority in cats uses the name Felis catus to describe the domestic cat, while Canis familiaris is slowly being replaced by Canis lupus familiaris.

The revised taxonomy of Felidae  that was released in 2017 does change how we classify wildcats. Classically, we recognized a single species of wildcat, Felis silvestris. The domestic cat is derived from a Near Eastern population, which was classified as Felis silvestris lybica.  There was another wildcat that lives Western China that was sometimes recognized as Felis sivestris bieti or Felis bieti. The big taxonomy debate in this genus was where to include this Chinese mountain cat into the greater wildcat species or have it be a species of its own.

The new taxonomy changes quite a bit of this. Felis bieti is now recognized as species, but Felis silvestris now refers to only European and Caucasian wildcats.  Felis lybica is the new scientific name for the wildcats living Africa, the Middle East, South Asia, and some parts of Central Asia, where it is sympatric with the Chinese mountain cat.  The fact that lybica and bieti exist in the same area without much gene flow is apparently the reason for elevating bieti to a species.  The reason for splitting up silvestris, though, had do with a deep mitochondrial DNA divergence between European and Caucasian wildcats and the rest of the wildcat species. Apparently, these two forms split from each other 173,000 years ago.

This revised taxonomy is really, well-supported with data, and I generally think it is right in its conclusions. However, I do think it made an error with this genus.

It retained Felis catus as a full species.  The same logic that says dogs are Canis lupus familiaris says that you cannot have a special domestic cat species either.

So the best way to classify domestic cats is as Felis lybica cata. You will probably only see this name written on this space, because unlike the literature on dogs, there is a noted deep adherence to Felis catus in the literature on domestic cats.

I honestly don’t know why there is such an adherence, because domestic cats are not that different from Felis lybica.  They come in more colors and coat types, but most domestic cats can live just as wildcats do. That’s why feral cats are an ecological hazard in so many places. They are quite effective predators, the ultimate mesopredator that found a niche living under the nose of man.

We don’t have as many good nuclear DNA studies on the various small cats as we do on various forms of the gray wolf complex, and this may be why there is a tendency to avoid a cladistic classification for the domestic form.

But if we’re doing this for dogs– and for good reason– we should be doing the same for cats. And the same for pigs and domestic mallards and domestic jungle fowl.

 

 

Read Full Post »

feral dog

Most feral domestic animals revert to a form that is roughly similar to their wild ancestor. You can see this quite dramatically in feral pigs. They generally evolve into a form that is about the same size and even coat type of the Eurasian wild boar. City pigeons look very much like the rock dove or “rock pigeon” that is their wild ancestor after just a few generations of breeding without human care.

Because village and pariah dogs tend to be mid-sized, it has been assumed that the wild ancestor of these dogs surely would have been on the smaller side as well. Therefore, the gray wolf simply could not have been an ancestor.

What actually drives the size of freely breeding and feral domestic dogs isn’t that they have some ancient alleles that force them into returning to an ancestral form.  The truth of the matter is that ecological niche and caloric restraints have a lot more to do with this phenomenon.

Dogs are unique among domestic animals in that they are the only domesticated form of large carnivoran. We have never domesticated any other species of large predatory mammal except for those Pleistocene Eurasian wolves that are at the base of domestic dogs.

Most domestic dogs are poorly adapted to living as predators, and they really don’t have to be. When dogs go feral in societies with extensive agriculture, they readily scavenge and hunt small prey. They dabble in various levels of omnivory.  Some dogs might be good at hunting deer, but deer are a lot harder to catch than garbage and groundhogs.

There is an extensive literature on mammal predator size and prey choice. The best known researcher looking at these issues is Chris Carbone, and in a 2007 paper called “The Costs of Carnivory,” which was published in POLS Biology, Carbone and colleagues looked at body mass of mammalian predators and their prey choices. If a predator weighed more than 20 kg, it hunted large vertebrates. If it weighed less than that weight, it hunted invertebrates or small vertebrates.

Larger predators get a much higher net energy gain by targeting large prey, and this large prey allows them to maintain their larger body size.

Feral and freely-breeding domestic dogs are not hunting large vertebrates. It is much easier for them to scavenge as mid-sized creatures. Natural selection would favor a moderate size, because any dogs that retained the large dog or large wolf alleles in the population would have a harder time feeding itself efficiently on these resources alone.

There are, of course, exceptions to this rule. In Uruguay, there was a population of feral mastiff-type dogs, which are called Cimarrón Uruguayo. These dogs were introduced by Europeans as working dogs, but some of them went feral. They were able to maintain their large size because they hunted livestock and game, and they were such a problem that the government placed bounties on them.  These dogs were living in a feral existence for at least 250 years, but they were able to retain a large mastiff phenotype. The feral mastiff is now being transformed into a standard breed.

However, the general rule is that village and pariah dogs tend to be significantly smaller than wolves, but this smaller size cannot be used to deny that dogs are derived from gray wolves. This smaller size is just more efficient for the ecological niche of feral and village dogs.

And it is poor reasoning to assume that dogs cannot be wolf derivatives simply because they do not evolve back into a wolfish form once they go feral.  Dogs have been domesticated for a long time, and their domestication is quite unique.  As the only large predator we have domesticated, ecological pressures create a different sort of animal than the original wild ancestor.

Read Full Post »

How did Komodo dragons survive?

dragon eats goat

Komodo dragons are the world’s largest lizard.  They are supersized monitor lizards that first evolved in Australia four million years ago.  One million years ago they arrived on the Wallacea Islands, where they fed upon a dwarf species of elephant. That elephant went extinct 50,000 years ago. The mainland Australian population of these lizards went extinct around the same time as those dwarf elephants.  The main prey of Komodo dragons now consists of introduced ungulates that arrived on those islands between 7,000 and 10,000 years ago.

That means Komodo dragons spent 40,000-43,000 years without large terrestrial prey sources, and if that is the case, how did they survive?

Well, a new paper in the journal Global Ecology and Conservation attempts to answer that question.

Apparently, Komodo dragons are an odd mix of the best ectotherms and the best of endotherms.  As ecotherms, they have the ability to rely upon limited food resources, and it just so happens that the oceans around their last island redoubts are quite diverse marine ecosystems. So the dragons would have plenty of marine food that they could scavenge. They also have the ability to reduce their growth rates to compensate for the lack of large prey species on the island, a trait that has been shown in the subfossil record. Remains of dragons that date to these lean millennia show that dragons were significantly smaller then than they are now.

Also, unlike most ectotherms, Komodo dragons, like virtually all monitor lizards, have the ability to adjust their behavior and try new food sources. When tourists scared off the ungulate prey of Rinca Island, the dragons simply started hunting macaques and raiding scrubfowl nests.

Further, the dragons could also live nicely as cannibals. Smaller dragons get eaten by the larger ones, and because the dragons produce far more offspring than could ever reproduce, the excess dragon young could have fed the adults quite well.

Humans also never really thought of these arid and semi-arid islands as good places to set up large scale agriculture, and because these islands were also devoid of native prey species, humans were not widely using them as places to hunt until deer, buffalo, and pigs were introduced.  When humans did settle the islands, there were enough dragons in the population that had “shy personalities” that kept them from causing conflicts with humans. These “shy” dragons are disproportionately female, and they could have passed these more retiring traits onto their offspring, which is why Komodo dragons are not killing people left and right. People likely killed off the bolder males when they first began to settle these islands, and in a species were the sex ratio tends to be biased in favor of males, any trait that would have increased a female’s survival would have definite consequences in the population genetics of the species. That means that the “shy” trait could have easily become expressed in the population, simply because humans would have low tolerance for aggressive behavior.  Dragons today generally avoid people.

Finally, females of this species are capable of reproducing via parthenogenesis. Males in this species are larger, and if conditions became so bad that all the large males died off, some of the females would still be able to reproduce anyway.  Because of how the lizards’ sex chromosomes work, they can only produce male offspring when they reproduce this way, which could be a way to restore males to a population that lost them through a lack of food resources.

Komodo dragons were once quite widespread across Australia and several nearby islands, but now they exist only on the islands of Wallacea. These islands are named for Alfred Russel Wallace, a co-discoverer of evolution by natural selection. Wallace noticed that the native animals of Sunda, which is the Malayan Peninsula and the Malayan Archipelago, are fundamentally different from the native animals of the islands just to their east.  The animals of Sunda generally have an Asian origin, while those of the islands to the east are more of Australian origin. The line between these islands is called the Wallace Line.

The dragons of Wallacea are of Australian origin. Their current main prey sources are all most of Asia origin. So in the Holocene, humans broke down Mr. Wallace’s Line, and the dragons grew back into their larger form. This larger dragon was the same one that hunted the megafauna of the Australian mainland, playing second fiddle to only the larger monitor called megalania (Varanus priscus).

I have often wondered what it would have been like to have seen the mammoths that lived on Wrangel and St. Paul Islands. These mammoths were the last survivors of a species that range over much of Eurasia and North America until 10,000 years ago, but they continued to survive on St. Paul Island for 5,600 years. They died off on Wrangel Island only 4,000 years ago, and they only died out because of a weird genetic mutation similar to the rex mutation in rabbits that made it harder for them to insulate their bodies on that cold island.

But by several accidents of their biology, the Komodo dragons have not undergone the same fate. They still exist as a relict population.

We have a hard time living with large predatory animals. They tend to inconvenience our way of life pretty badly. However, the people of these islands do benefit from the dragons. They attract a lot of tourists and their dollars. There is real economic benefit to having such creatures roaming about.

But I don’t know how long this can last.  Because the dragons have these shy behaviors where they avoid humans, increased tourism on these islands could greatly stress them, making it harder for them to thrive and breed. These concerns came at about the same time of a mass arrest of an animals smuggling ring that had 40 dragons in its possession, which has led the Indonesian government to ban tourists from coming to Komodo Island in 2020.

If the islanders cannot make money from tourists, though, it is very likely they will try to make some money selling the dragons to smugglers, and if authorities are not on top of things, the Komodo dragon might not survive the Anthropocene.

Read Full Post »

Mule deer dreams

mule deer stott

One of my dreams is hunt mule deer in the West. I don’t care where in the West. I just want to go out on into that big country, wander around the rocks and cliffs and sage brush, climb out onto a high vista, and glass the scenery for antlers.

I am from the land of white-tails. White-tails are the ultimate habitat generalists, and in “settling” and “civilizing” these Eastern lands, we have create a paradise for them. They can wander the forest devouring acorn after acorn, and they can grow fat and glossy in the fields of soybeans and corn.

The mule deer is a different animal. It migrates from higher elevations to lower ones. It likes much more open forests and grasslands and sagebrush steppes.

Current taxonomy says that the various forms of mule deer and the two subspecies of black-tailed deer represent a single species, but the black-tails are creatures of the Pacific Coast forests. They are different entity in my mind, though I’m sure the deer exchange genes where one form’s range runs into another without any consideration of human classification.

These arid and semi-arid land mule deer, though, are what has me fascinated. The mature bucks are rather large and impressive, more so than the equivalent white-tails. But I do not think of them so highly because they are larger. I think of them so highly because they have a Western mystique. They are not such habitat generalists in the way white-tails are.

They are beings of a more specific landscape, a landscape that is under threat in part because oil and gas development, housing speculation, and overgrazing by livestock are taking their toll. The spread of cheatgrass, which grows into lovely fire tinder, is also to blame. The fires that spread from its stalks wipe out the sagebrush, which the mule deer rely upon to feed them through the winter.

So the white-tail basks in the glory that is our civilization, as the mule deer continues to retreat and withdraw from it. And in this, I find their true appeal.

I hope that when I will get a chance go West on a mule deer hunt before it is too late. I can see a time when the deer will become so hard-pressed that hunting opportunities will be curtailed, even abolished. I hope that we will be wise in our understanding what is happening to these deer before they lose the range and forage on which they so clearly depend.

To hunt mule deer is to go nearer to the wilderness, perhaps even into it.  It is an odd little romantic dream of mine at which I’m sure some Westerners will laugh.

But these deer still exist in the sage and rocks and grasses. They are the setting sun, casting away beyond the Western horizon, beckoning me across the continent to cross the prairies and the mountains.

And someday, I hope to. Before it’s too late.

Read Full Post »

Older Posts »

%d bloggers like this: