Feeds:
Posts
Comments

Archive for January, 2012

This image comes from Toy Dogs and Their Ancestors  (1911 edition) by Lady Wentworth.

The expressions on the faces of the two chin is priceless!

Japanese chin, which were then called “Japanese spaniels,” really haven’t changed much in the past century.

About these ads

Read Full Post »

African village dogs are just as genetically diverse as those in East Asia, and they have been found to be closely related to Middle Eastern wolves.

From National Geographic:

Labradors may be the most popular breed of dog, but the most populous kind is no breed at all. That distinction goes to the humble village dog scratching out a semiwild living in and around human settlements.

While a postdoc at Cornell University a few years ago, Adam Boyko became curious about the little-studied village vagrants. Though dogs were first domesticated 20,000 to 15,000 years ago, most breeds go back only a few hundred years. Perhaps village dog DNA might shed light on the long, early history of domestication, when canines were hanging around humans yet not under our domain. But how to get samples?

As it happened, around the same time Boyko’s brother Ryan had married, and he and wife Corin were looking for a cheap honeymoon off the beaten track. The three Boykos decided to merge their two quests. Adam—now at Cornell’s College of Veterinary Medicine—­obtained a grant, then enlisted Ryan and Corin to spend their honeymoon traveling around Egypt, Uganda, and Namibia, befriending villagers and local vets. They collected DNA from more than 300 village dogs.

When the samples were analyzed, most of the village dogs turned out to be as closely related to wolves as they were to fully domesticated dogs. Rather than being mixed-breed mutts that had gone feral in historical times, the village dogs had been eking out an existence on the human fringe for millennia. Their genomes thus reflected a state of early domestication, before artificial selection and inbreeding directed by humans had taken over. “When you are looking at village dogs,” Adam Boyko says, “you have something more akin to natural selection, albeit in an environment that’s managed by humans.”

Unexpectedly, the study also helped to challenge the reigning view on the place where dogs first appeared. Fossil evidence had already pinned the transition from wolf to dog somewhere in Europe or Asia, and a 2002 study had shown that East Asian village dogs were more genetically diverse—an indication that wolves had first been domesticated in East Asia. But the Boykos’ 2009 work found that the African village dogs were just as diverse as the East Asian ones. Some also carried a genetic signature shared with Middle Eastern gray wolves, supporting research by Robert Wayne and Bridgett vonHoldt of UCLA that points to the Middle East as the likely cradle of dogs.

The Boykos continue to expand their sample collection, with another expedition planned for Africa. And they’ve also begun using the same techniques to solve a related mystery: the strange disappearance of native dogs in South America. We know from the historical record that Native Americans had dogs. But previous population surveys in the Americas turned up only dogs with European heritage. “How do you ship so many dogs across the world that they completely replace the native dogs?” Boyko wonders, suspecting that in fact there may still be village dogs with native DNA in the remotest areas of the continent. So in August the three Boykos packed their bags and headed into the jungles of Peru, searching for the lost American dog.

I have written about the discovery that African village dogs were just as genetically diverse as East Asian dogs– which in part falsifies the hypothesis that dogs originated in East Asia. People like that hypothesis for some odd reason.

I did not know that the Boykos had discovered that some these African village dogs showed an affinity with Middle Eastern wolves,  which I think is very supportive of the hypothesis that Middle Eastern wolves– or very close relatives of the– are the most important population that contributed to the domestic dog.

Now, it doesn’t mean that phenotypically distinct domestic dogs first appeared in the Middle East. It just means that this population contributed to the majority of dogs we have today. The small dog gene that is found in purebred dogs is also found in some Middle Eastern wolves–likely coming from Canis lupus arabs. The smallest members of that subspecies weigh only 25 pounds.

I’m very excited that the Boykos are now looking at Latin American dogs to see if any possess indigenous ancestry. We know that virtually all Native American dogs in the US and Canada have largely been swamped with Western dog blood. Testing village dogs in remote areas of Peru might yield some interesting results, but keep in mind that “double-nosed” village dogs were found in Bolivia a few years ago. They likely derive “double-nosed” pointers that the Spanish brought over. Native peoples liked to use European dogs for the hunt, and in the colonies that later became the United States, laws were passed to prevent European colonists from selling their dogs to the Indians.

Native Americans’ preference for Western dogs would have been an important factor in the extinction of Native American dog strains.

Another important factor is that these dogs may not have had much resistance to European dog diseases. Just as their human owners were no match for small pox, it is possible that common diseases in European dogs were quite devastating to Native dog populations.

And then there is also the simple fact that Native peoples were conquered– and in some cases, exterminated.  Massive social disruption leads to people not being able to care for their dogs– much less selectively breeding them. These dogs wound up wandering the countryside, where they either melded into the wolf or coyote population in North America or were shot on sight.

Any dogs that proved useful to the new order in the Americas were quickly absorbed into the growing Western-derived dog population.

To answer the Boykos’ question from an historical perspective, the Spanish were bringing over scores of dogs. Dogs were a major tool of conquest and colonization. The Navajo and Apache herders use their dogs as livestock guardians– a technique they got from the Spanish. The sheep they keep are derived from an old Spanish strain, and it is possible that their dogs trace to Spanish and maybe some  remnant Native American dogs.

It will be interesting to see if the Boykos’ work reveals any clues to the extinction of Native American dog strains in South America.  It will also be interesting to see if they find any dogs with clear indigenous ancestry. As far as I know, only the dominant hairless mutation that is found in xoloitzcuintli, Peruvian Inca orchids, and “Chinese crested dogs” has been traced to the Americas before the arrival of Columbus.

It will also be interesting to see if any of these dogs, if they prove to have ancestry from indigenous dogs, share signatures with North America wolves or coyotes or with wolves from East Asia. The VonHolt and Wayne study mentioned in this article found that certain East Asian breeds have an affinity with Chinese wolves. Because Native Americans came to the New World via Asia, it would make sense that some of these dogs would show some affinity with Chinese wolves– just as these East Asian breeds do.

Interesting questions.

I don’t know if they can be answered!

See related post:

Read Full Post »

You know those game ranches that produce trophy animals for people to hunt?

You know– the ones that both the animal rights activists and the self-styled defenders of the “true hunt” defame?

Well, they are actually saving endangered species! And the US Fish and Wildlife Service used to agree!

Check out this 60 Minutes piece on the role that these ranches are playing in saving certain endangered species.

I have a very different view of these ranches than I once did. I’m opposed to canned hunting in which people shoot animals in cages, but I have nothing against these well-run game ranches.

Altruism alone won’t save many endangered species. Economic value is a very is very important conservation tool, whether people want to admit it or not.

Read Full Post »

Talk about being in the right place at the right time! I’m hoping they are in a vehicle, because I would hate to be near a cow moose that is that irate.

This is amazing footage!

Source.

 

 

Read Full Post »

San Nicolas island foxes (Urocyon littoralis) are thought to be least genetically diverse of all vertebrates. However, they have been able to maintain diversity and heterozygosity of their MHC haplotypes.

On my previous post entitled “Why is inbreeding bad?” I noted that one of the real issues with inbreeding is an impaired immune system as the result of losing diversity and heterozygosity in MHC/DLA haplotypes.

The MHC stands for the Major Histocompatibility Complex.  The MHC is cell surface molecule that is encoded by a relatively large gene family.  The MHC  molecule controls some of the actions of the leukocytes, “the white blood cells.”  As you might remember from your high school health class, leukocytes are the blood cells that act as police, taking out infectious diseases and foreign materials, including cancerous cells.

Possessing a greater diversity in MHC haplotypes allows the organism a heightened ability to control what leukocytes do when exposed to a variety of challenges to the immune system. Reduced diversity winds up restricting the immune system’s ability to fight disease.  Possessing a heterozygous MHC haplotypes also provides greater immune resistance than possessing homozygous MHC haplotypes.

In humans, the MHC is called the human leukocyte antigen system, usually abbreviated as HLA. In dogs, it is called the dog leukocyte antigen system, which is abbreviated at DLA.

One cannot look at an organism and tell what its MHC haplotypes are. It’s not like looking at fur or hair color.

And as a result, these haplotypes are very easily lost within a closed registry system.  Often, the haplotypes not lost entirely within a breed or strain, but because of the popular sire effect and continuous linebreeding  from “the best,” a huge percentage of the population in any one breed can be quite homozyous in its MHC haplotypes.

This has real health and welfare effects.  Autoimmune diseases are becoming more and more common in purebred dogs. Some breeds are highly susceptible to cancer, which might be partially the result of the decrease in MHC diversity of dogs within the closed registry system.  Allergies are also likely implicated to this reduction in MHC diversity and heterozygosity. The MHC also has some effect upon reproductive cells, which is one reason why certain breeds and strains have issues with fertility.

So what can be done?

Well, the easy answer is to do away with rigid closed registry systems and allow the different dog breeds to exist as very genetically diverse populations.

However, it is possible to breed for great MHC diversity in domestic dogs, even within the closed registry system.

To understand how this is possible, we will have to change species again.

Take the San Nicolas population of the island fox (Urocyon littoralis). This population is considered the least genetically variable of all sexually reproducing animals.

However, despite its lack of genetic diversity, this population of island fox has relatively diverse MHC haplotypes.

How does it do this?

Well, a study led by Andres Aguilar (2004)  found that the San Nicolas foxes likely were able to maintain their diverse MHC haplotypes through what is known as balancing selection. Balancing selection occurs when population keep multiple alleles actively maintained at frequencies that are higher than the mutation rate. It almost always happens within populations in better for an organism to be heterzygous for certain alleles than homozygous for them.

As we have seen with MHC haplotypes, it is better to be a heterzygote, so there is a strong selection pressure for the foxes to keep their MHC haplotypes diverse.

One way in which they likely do this is that they choose mates that have MHC haplotypes that are different from their own.

This might sound a little crazy, but even humans have innate mechanisms that are designed to keep our MHC haplotypes diverse.

There is a famous study in Switzerland that asked women which men were most attractive by smelling the shirts the men had slept in for two nights. Almost without exception, the women selected the men who had different MHC haplotypes from their own. The pheromones that are connected with sexual attraction in humans are also giving out genetic information such as what MHC haplotypes a potential mate might have.  And it’s so innate that women are able to obtain this information without understanding exactly what they are responding to.

It’s likely the same way in island foxes, which, like humans, typically reproduce within a bonded pair system. Foxes, like all wild dogs, are pretty particular about their mates. After all, the survival of their offspring is dependent upon having a partner that can provide for them.

Domestic dogs, for whatever reason, don’t seem to be as particular about their mates, and thus, it has been easier to selectively breed them.  Wolves and other wild dogs very rarely inbreed, but it is relatively easy to get dogs to inbreed and to do so for multiple generations.

And as a result, it has been easier for different breeds to lose their MHC haplotypes.

Further, it is not just the mere number of haplotypes a breed possesses. Heterozygosity has proven to be more important in determining immune health than just possessing a certain number of haplotypes.

That means that within an inbred population, there has to be some conscious effort to maintain both diversity and heterozygosity.

That is pretty hard to do when one is breeding for physical or behavioral traits– and the immune system genes cannot be readily ascertained.

Well, we do have a solution. Genoscoper currently offers an MHC II test, which would allow breeders to see what haplotypes their dogs posess and what to do with them. Mars Veterinary also offers a test that examines the MHC (among other things). It is called Optimal Selection from Wisdom Panel, and it was initially tested with breeders affiliated with the Dandie Dinmont Terrier Club of America (A NEW GENETIC BREEDING TOOL ON THE HORIZON (1)). Over a two year period, this selection tool has allowed Dandie Dinmont breeders to increase their litter sized from 2.75 to 4.0 puppies per litter. Dandie Dinmonts are a rare terrier breed that has issues with genetic diversity, and these tests could be a boon for breeds that have very small founding and effective populations.

So science now allows for us to do with domestic dogs what the San Nicolas island foxes were able to do on their own.  We can maintain relatively inbred populations and still keep the MHC haplotypes diverse and heterozygous.

However, here are some caveats:

First of all, virtually no dogs are bred without some eye to competition. Competition, whether in show or working trials, has a selection pressure of its own, and a breeder has to considered a wide variety of issues before choosing which dog to breed with which other dog. As I’ve noted before, MHC haplotypes are hard to see, so how many breeders would choose diversity and hetrozygosity of MHC haplotypes over the ability of the dog to win in the show ring or in the trial?  I would like to think that very few breeders would choose immune health over ribbons and titles, but that’s probably not the case.  Keeping the MHC diverse and heterozygous is a long-term project, and it requires a bit more dedication and discipline to breed for than physical or behavioral traits.

Further, breeders have to balance a wide variety of issues when selecting which dogs to breed, and MHC haplotype diversity alone should not be the sole criteria.  Other issues with temperament and hereditary diseases have to be considered in light of the MHC.

Finally, many of these breeds have either entirely lost MHC haplotypes or certain haplotypes are very rare within the breed.

You cannot do DIY balancing selection when you don’t have the haplotypes in the first place.

Even if we might have these tools, one should keep in mind that it is much more cost effective and easier to try to maintain genetic diversity within breeds and strains in the first place. It makes much more sense to keep breed registries more open and then operate selective breeding principles within much more diverse populations.  Breeding within much more diverse populations requires some understanding of how different traits are inherited, but one can readily learn these skills. It is not rocket science, but one can figure it out. If people living thousands of years ago0–before there was even a Mendelian theory of inheritance– were able to produce so many different types of dogs, then we surely can.

DIY balancing selection can be a tool within conservation genetics, but I think it has to be paired with a fundamental understanding of how population genetics works.

Otherwise, you’re going to get into silly arguments with people who think that you can just inbreed and inbreed without consequence. No rare dog breed can be saved in the long term if its immune system doesn’t work properly.

It’s really that simple.

In the end, selecting for diverse and heterozygous MHC haplotypes within a limited gene pool is less preferable than trying to maintain genetically diverse strain.  We have intentionally reduced genetic diversity within dog breeds and strains, yet as a population, dogs remain one of the most genetically diverse of all domestic animals. We have the ability to correct some of the errors without resorting to sophisticated genomic technology, but because the dog culture at large values purity and homozygosity at all costs, we are left looking at the only other option available.

Inbreeding requires so much scientific knowledge and acumen to pull off correctly that it really shouldn’t be done. And the validity registry systems that ultimately reduce dog breeds to inbred populations needs to be questioned.

Read Full Post »

Reggie

This is Reggie. He (we’re assuming it’s a he) is a green spotted pufferfish (Tetraodon nigroviridis).

He’s two inches long and sleeps on the bottom of the tank.

His species has the smallest genome of any known vertebrate.

Read Full Post »

Source.

It is amazing how similar their behavior and mannerisms are to domestic dogs, even though they are more distantly related to domestic dogs than we are to chimpanzees

Read Full Post »

Older Posts »

Follow

Get every new post delivered to your Inbox.

Join 989 other followers

%d bloggers like this: