Monday, December 17, 2012

Who were the first dogs? Explaining genetic diversity

Scientists still don't know. But whoever the first dogs turn out to be, if they're not extinct, they'll be the dogs with the most genetic diversity - almost as much diversity as the wolf.
The First Dog by Benjamin Cheever
The gray wolf, the canid with the most genetic diversity (let's say100% ), is the progenitor of all domestic dogs.

The Empty Nest

Dogs move in packs.  Each time dogs broke away from the original family and moved on to better opportunities, they would mate with close cousins who'd migrated with them.  Their offspring would have had less genetic diversity than their ancestors' because the parents were more closely related.  As this process continued over thousands of years, diversity was reduced.

Humans, by applying artificial selection, have created smaller and smaller populations. If it's a very small population, it's called a bottle neck. In the case of dog breeds, the least amount of diversity will be a breed that's gone through the narrowest bottle neck.

The Norwegian Lundehund is a good (but unfortunate) example.

The ancestors of the Lundehund were not a breed per se, but rather a landrace, a local variety of domesticated animal that developed largely by natural processes.  Their natural environment included rocky surfaces, craggy cliffs and steep fjords.  For thousands of years the Lundehund was a genetically diverse balanced population.

The dog in its natural environment.


About a hundred years ago, the landrace was artificially "perfected" to negotiate rocky cliffs to hunt Puffin birds, now an endangered species. Some breed diversity was lost.
Puffin Bird
Two distemper epidemics, the first in the mid 1940s, wiped out all but a handful of dogs. The breed (current population about 1500-2000) was rescued with just six dogs. Unfortunately, five of those were descended from one mother.  Small groups of individuals who are this closely related, whether they be human like the Hapsburgs, or canine like the Lundehund,  have a high incidence of genetic disorders.
The Hapsburgs had many genetic problems.
Hemophilia was probably the worst.

The Lundehund suffers from a life threatening digestive disorder (Lundehund gastroenteropathy) that causes the dog to be unable to absorb protein and nutrients from food.  Not all dogs are afflicted, but all Lundehunds are carriers.  Although the disease can be managed, there is no cure.  The average age of death is 7-8 years.

The unique feature of the Lundehund is it's polydactyle foot with fully formed, jointed and muscled toes.  Note the six toes instead of the normal four. I wonder if she can open the refrigerator door.



In addition, the dog has extreme range of motion in its shoulders, neck and ears. (The ear canal opening can be controlled by ear movement). These distinctive traits, found only in the Lundehund, likely developed from natural pressures the dogs experienced thousands of years ago.  If breeders were to cross the Lundehund with another breed to increase diversity and reduce the incidence of disease, these extraordinary features would be lost forever.   Breeders face difficult decisions.

To read more about the unusual Norwegian Lundehund, click here


6 comments:

  1. Love those feet, have never seen a dog with the extra toes.

    Debbie

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  2. "If breeders were to cross the Lundehund with another breed to increase diversity and reduce the incidence of disease, these extraordinary features would be lost forever."

    Thank you for a statement that is not only absolute nonsense, but will feed into the belief that many purebred breeders have about dog breeds being different species. Depending on the inheritance of the 'special' traits of the Lundehund, you may be able to return to those traits within only two generations (one outcross, one backcross.) Dominant traits, of course, will occur in some of the pups in the first cross. Please see the Boxer/Corgi cross to see how offspring from a cross between two very different breeds are chosen to perpetuate the desired traits:

    http://www.steynmere.com/GENETICS.html

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  3. Responding to Jess' comment regarding maintaining the Lundehund's unique traits through backcrossing and outcrossing: In most cases this is true, but not so for the Lundehund. Dr. Mark Neff, U.C. Davis geneticist explained, "Most breed-defining traits are shared by multiple related breeds. For example, I would predict that the genes for pointing behavior are common to perhaps a dozen or more pointing breeds. So one could resurrect a breed by bringing together the right combination of genes from related breeds. This won't always work because there are some characteristics that truly are unique, such as polydactyly in the Lundehund."

    Read the entire interview here http://www.thebark.com/content/deconstructing-gene-pool?page=4

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  4. This comment has been removed by the author.

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  5. Whenever a particular dog breed becomes popular, you can bet within the next ten years we'll have done irreparable damage to that breed, for the sake of a flatter nose, a fluffier coat, or a certain way of posing that for some reason wins the blue ribbon at the dog show. Our intervention from a breeding perspective should only be to promote the health and long happy life of the dog.

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  6. We all wonder, "Why would anyone create a dog that can't breath, or one so deformed it can't run." But another question to ask (and one I don't have an answer to) is "Why do humans see these exaggerated traits as endearing rather than cruel and inhumane?"

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