The Canaan Dog Gene Pool
[This article originally appeared in the Spring 2002 edition of Desert Tracks, the award-winning newsletter of the ICDCA and is reprinted with permission.)
Founders of the North American Canaan Dog Population
One day I decided to trace back the pedigrees of Canaan Dogs in North America as far as I could, back to their wild-born or Bedouin-owned ancestors. The result surprised me greatly. All living Canaan Dogs in North America trace back to just 23 founders (for our purposes a founder is an ancestor whose pedigree is unknown). The following 10 dogs and 13 bitches appear to be the founders of the North American population:
|Male Founders||Reg Number|
|Ron Mifratz Haifa||IKC 379|
|Paz (=Blacky)||CD 48|
|Toro of Isfijah||IKC 366|
|Zakief me Yerushalayim||CD 147|
|Guri me Beit HaKerem||ISBR 36611|
|Noded me Arad||ISBR 8092|
|Patpatan me Plugot||ISBR 5549|
|Ben bar me Jericho||ISBR 7748|
|Tani me Hashfelah||ISBR 7370|
|Female Founders||Reg Numbers|
|Lady me Kurdani||CD 93|
|Dina me Darom||IKC 421|
|Sufa me Petra||ISBR 5329|
|Mookie of Talpiot||IKC 159|
|Bat bar me Jericho||ISBR 7749|
|Yekutiella me Yerushalayim||ISBR 5651|
|Aliza me Ofra||ISBR 7168|
|Noga me Tuba||ISBR 8093|
|Levana me Abu Aguiela||ISBR 8093|
|Minto's Libyan Jewel||U0096341V01|
This is a complete listing as of 1998, the last year for which I have
pedigrees on all registered dogs. Until that year there had been about 60 registered imports to North America, but not all of them were used for breeding, a few bloodlines died out, and many had similar ancestry and so added no new
founders. At least 20 dogs have been imported since 1998 and I have pedigrees for only a few of these but it is doubtful that they added many founders as most are related to other dogs already in this country.
It is entirely possible that I've overlooked a few founders. If you perform this exercise on your dog's pedigree and come up with some names not on the list above, please let me know.
The more founders the better, because the number of founders limits the breed's genetic diversity. Once the studbook is closed you can conserve the diversity that the founders possessed, or lose it, but the only way to increase genetic diversity is by adding new founders.
How does this compare with other breeds? Basenjis descended from about 15 founders until increasing health problems necessitated the opening of the AKC studbook to accept a few additional founders brought in from African villages. Many of the more derived breeds such as Dobermans were created by crossing several different breeds. Because these founders were of different breeds genetic diversity may initially have been high, but the small founder number and consequent inbreeding led to the health problems plaguing many of these breeds today.
Dog breeding typically reduces genetic diversity over time. Breeders attempt to produce dogs that fit the breed standard. Breeding to a standard increases predictability but reduces genetic diversity, because the standard emphasizes a narrower range of variation than is present throughout the breed. Achieving a balance between uniformity of type and genetic conservation is difficult. All too often the "hype" about "breed type" causes breeders to emphasize a desired appearance over preservation of the gene pool with the result that genetic diversity is lost. And once variation is lost it can never be regained unless new genes are introduced from another source.
If human preferences change, selection for characteristics which deviate from historical breed traits may also deplete the genetic heritage, as genes which were once desirable are discarded, with resultant narrowing of the gene pool. Any of these changes which cause unnecessary genetic loss is dangerous.
Why care about genetic diversity?
Why is loss of diversity dangerous and what are the benefits of diversity? Diversity is essential for selection. Selection occurs any time animals in a population do not contribute their genes equally to the next generation. Genetic diversity is essential for natural selection, which shaped the Canaan Dog breed, and also for subsequent human selection of the best breeding stock. There can be no selection, natural or otherwise, without choices from which to pick. The intensity of selection then affects subsequent diversity: intense selection for particular traits reduces variation more quickly than relaxed selection.
With an endangered species we hope to preserve the full range of variation still present in the population in order to change the species as little as possible until it is self-sustaining again. This is not entirely applicable to dog breeding. For example we don't particularly want to preserve the gene that causes rough coats in Canaan Dogs. But within the range of acceptability we do need diversity. Studies of many species have shown that reduction of genetic diversity through inbreeding is associated with reduced fertility and increasing expression of genetic diseases. The immune system, in particular, relies on genetic variability to cope with new strains of microbes encountered. If a virus mutates and no members of the population possess a genetic variant conveying resistance, the whole population may go extinct. If a breeder has a Canaan Dog with a physical flaw and all other Canaan Dogs have the same problem, to whom can the dog be bred to improve the trait in its progeny? We need variation in order to give us somewhere to go when undesirable traits inevitably appear and so that we can plan matings to correct the problem. It is for this reason that agriculturalists are realizing the importance of preserving ancient livestock breeds, and plants such as maize, the ancestor of modern corn.
Breeding strategies defined
Dog breeders usually define inbreeding as mating two immediate relatives, for example father to daughter. A parent passes half of their genes to each of their offspring. This fraction of genes identical by common descent is referred to as the inbreeding coefficient and is a measure of the degree of genetic uniformity. A father and a daughter share 50% of their genes. Inbred offspring produced by mating a father and daughter will, on average, possess 75% of the same genes as the "father/grandfather" instead of the usual 50%. Such matings produce consistency by reducing genetic variability. This process is blind as to whether the traits being consolidated are good or bad. Many genetic diseases are coded for by recessive genes and the danger is that these hidden genes will be inherited in double dose and therefore expressed in inbred offspring. Inbreeding coefficients of 30% or more may be associated with reduced fertility and viability. It is not coincidence that most human cultures have taboos against marrying a close relative, with the cut-off point of what constitutes "close" typically being first cousins (who share only 12.5 % of their genes). Population geneticists recommend keeping the increase in the average inbreeding coefficient below 5% per generation (not per individual) to minimize gene loss.
Linebreeding is often described as mating more distantly related individuals (ie. first cousins or beyond) who share some ancestors in their three-generation pedigree. Linebreeding is a less intense form of inbreeding with similar risks and benefits.
Outcrossing is the mating of two unrelated individuals. In domestic animal breeding it is often called linecrossing because individuals from two different bloodlines are being mated. The outcome of such crosses is less predictable, but hybrid vigor resulting from new genetic combinations is often observed.
Recommendations for the Canaan Dog breed:
I would like to begin with a quote:
"Breeders who work with captive populations of feral breeds find themselves conserving a gene pool selected by the harsh hand of natural selection. It is practically impossible to replicate such selection pressures under human management. The best course is to maintain the existing genetic variation within a population, particularly all of the founder bloodlines... Even with a careful conservation program, a feral breed will gradually be transformed under human management, and at some point is no longer truly feral. Conservation breeding can, however, ensure that a good portion of the genetic diversity represented by feral breeds is not lost."
This quote comes from a book I highly recommend: Sponenberg, D.P. & C. J. Christman. 1995. A Conservation Breeding Handbook. The American Livestock Breeds Conservancy, P.O. Box 477, Pittsboro, NC 27312. email@example.com A great buy at $12.95! Although the authors are addressing the conservation of rare livestock breeds, much of what they have to say can be applied to dog breeding as well.
1. Don't define the breed standard too narrowly
A standard that specifies a narrow range of acceptability reduces genetic variation as breeders strive to produce dogs that fall within the parameters outlined. The narrower the range, the more dogs that won't meet the criteria and will likely be dropped from the gene pool.
2. Don't put all your 'eggs' in one basket
One important aspect of conservation is the maintenance of multiple populations around the world. This makes the breed less vulnerable to extinction. In the event that some adversity such as distemper, parvo, rabies eradication programs, or war causes the loss of one population, others remain intact. As an example, there were some Canaan Dogs in South Africa but nothing has been heard of them in some time. Populations can be lost through disinterest too!
Populations that are isolated from one another over a long period of time typically begin to diverge from one another. Remember the ICDCA's concern that an Americanized version of Canaan Dog was being created, as has happened with so many other breeds? I have been pleased to see the recent exchanges of Canaan Dogs between breeders of different countries. Unless the dog contains genes that will bring a new founder into the population, an exchange doesn't add diversity, but it does keep the genetic material shuffled to minimize inbreeding and divergence.
3. Maintain an adequate world population size
Geneticists give a ballpark figure of 500 breeding animals as a minimum population size needed to conserve genetic diversity. This number is admittedly crude and will vary depending on the number of founders and the amount of diversity they contained, lifespan, mating system, etc. The rationale is that a smaller population is more prone to genetic drift, in which some subset of genetic variation is present but not the full gamut that a larger group would contain. In North America there are over 500 living Canaan Dogs, but my guess is that less than 200 are being used for breeding; most are spayed or neutered. Even if we consider the world population of domesticated Canaan Dogs the total number of breeding animals is probably less than 300. Numbers are already increasing due to rising interest in the breed. We need to slowly increase the number of breeding animals so as to have more individuals to chose among and before we can afford to be very choosey. Obviously there are attendant problems which we are already seeing: those who have no business owning a Canaan Dog getting into the breed, breeders accumulating too many dogs, all creating the need for breed rescue. I am strongly against pressuring people to breed. But perhaps there are some compromises we can effect, such as better support for new or small-scale breeders to help them place dogs so that they don't burn out after the first litter. Perhaps contracting with puppy buyers who "only want a pet" to leave the dog intact until its quality can be assessed and then through co-ownership or other contract (such as leasing back the dog) producing one litter from it before neutering. If the owners of a bitch wish, they could whelp the litter while the breeder takes responsibility for placing the puppies, which is the most daunting aspect of breeding. Or the bitch could go back to the breeder for the duration of the whole process. I know that these things are already occurring to some degree, but I am also aware that many first time breeders have difficulty placing puppies. Perhaps there is more that could be done.
4. Use a larger number of individuals for breeding
To conserve genetic variation while we grow the population, we need to use a greater percentage of the population for breeding, especially males, rather than over-relying on a few superlative studs who create genetic bottlenecks. If only a few males are used to produce a generation the genetic diversity will be greatly reduced regardless of the number of females to which they are bred. The genetic bottleneck becomes even more serious if these few males are related to one another. A sound dog who is somewhat lacking in appearance but represents a rare bloodline might be more desirable than a superior dog whose genes are already well-represented in the population. Increasing the number of the less numerous sex (usually stud dogs) has more impact than similar increases in the number of the more numerous sex (usually bitches). Until we build up a large population, all healthy show quality dogs ought to leave behind at least two breeding offspring, thereby on average passing along the full complement of their genes.
As an example of genetic bottlenecks within our breed, consider that the large breeding kennels of Father Robnett, Lorraine Stephens, and Terry Bagley are now represented in the present day by very few individuals, such as Briel's Hatikvah bat Ariel. Who would have thought that so few genes from the dogs of these important kennels would remain? As delightful as Hatikvah was, it is impossible that she contained the full range of genes found in the dogs of these kennels; a large subset of the genes have been irretrievably lost and the remainder under-represented in the North American population.
5. Maintain Distinct Bloodlines
Total miscegenation isn't the answer either, as where then can a breeder turn to find unrelated animals for outcrossing? Ideally there should be a minimum of 3 to 6 distinct bloodlines within the breed. This allows breeders to alternate between line breeding and line crossing.
A possible scenario is as follows: Perhaps there are 6 separate bloodlines. Each breeder linebreeds within their bloodline to produce consistency and keeps the best linebred male offspring as replacement males and a few of the best linebred females. Occasionally (perhaps every third litter?) a linebred male from another bloodline is used as an outcross. The breeder keeps the best female resulting from this outcross but all outcross male puppies are sold. Keeping only linebred males rather than linecross males maintains distinct bloodlines for outcrossing, rather than miscegenation. Bringing in linebred sires from different bloodlines controls inbreeding while keeping bloodlines distanced. After several generations, if there is a trait that needs improving, an unrelated male should be sought that is superior for it. This male will replace one of the breeder's linebred males (bringing in 100% new genes). If improvement isn't needed at this time, a new bitch could be added instead, bred to the current linebred sire to conserve his genes, and her son used as a replacement for that sire (50% new genes from the dam, 50% linebred genes from the sire).
6. Identify individuals descended from rare founders and use them for breeding:
Most of our dogs carry the "blood" (genes) of founders Birion and Toro, who were bred extensively. But the genes of other founders are not well-represented. As an example, Shoham me Shaar Hagai, imported in 1991, added a new founder, Tani me Hashfelah, to the population. To the best of my knowledge Tani is represented in no other bloodlines in the USA and there are very few intact descendants of Shoham. If these descendants are never used for breeding the number of Canaan Dog founders may be reduced to 22. It is important that dogs descended from new founders or rare founders be used for breeding so that their genes are not lost from the gene pool. Again, once they are gone they can not be retrieved unless other intact descendants survive elsewhere in the world and are imported to this country. Much less risk and expense to conserve what we already have. We should make the identification of dogs who carry a rare bloodline a priority.
Breeders: if you own a male dog from a rare bloodline, or one that is superlative and has not been over-utilized, by all means have semen collected and stored. This might be another strategy to use when a puppy buyers' pet quality male turns out to be nicer than you thought; get some semen before neutering. This is also a hedge against accidents that might otherwise have removed a good dog from the gene pool. The Canaan Dog is a natural breed so I normally advocate against artificial insemination (AI). Preservation of rare bloodlines is the one of a few contexts in which AI makes sense for Canaan Dogs.
8. Obtain new founders
We are very lucky there are still nice feral and Bedouin-owned dogs in Israel. We can not predict how long it will be possible to obtain good quality dogs from the desert so we ought to take advantage while we still can. This is easy to say from this country, but the burden falls on Israelis because the three generation pedigree required by US registries severely curtails the rate at which we can add new genes to the gene pool. Consider again that a parent passes half their genes to each offspring so when the requirements for registration are met only 1/8 of the founder's genes remain in each of their third generation descendants ( Founder 1st generation 2nd generation third generation). To conserve approximately 100 % of founder's genes we need at least 2 breeding descendants in the first generation, 4 in the second generation, and 8 in the 3rd (registerable) generation. There is probably not much we can do except encourage and support Israeli breeders willing to do a miun in Israel. We can help place dogs from early unregisterable generations with owners in this country who just want a neutered pet and don't care that it lacks an official pedigree. We can assure Israeli breeders that the third and subsequent generations will be eagerly sought by breeders to broaden the gene pool in this country and others.
You may have noticed that some of these recommendations appear contradictory. This results from the tightrope we walk between consolidation of type and maintenance of diversity, trying to maintain discrete bloodlines while preventing too much divergence, and so forth. Each breeder will have to find a balance with which they are comfortable. Because there are no easy answers, breeding will always remain an art. But raising our awareness of these issues will help us preserve the Canaan Dog's genetic heritage.
© 2002-2003 Israel Canaan Dog Club of America