inbreeding

[Liz P]

http://www.sciencedaily.com/releases/2009/...90402171440.htm

 

Many people who practice tight inbreeding in purebred dogs use this population of wolves as proof that inbreeding isn't always bad.

[diane allen]

Wow - that is really interesting.

It says, "The four packs there comprise 24 wolves, all descended from one female and one or two males who crossed an ice bridge from Canada during an unusually cold winter in the 1940s." and the steady population seems to be around 24 now.

 

How many domestic bred dogs are descended from such a similar low number? Anybody know?

 

Nonetheless, Liz, a point well taken!

 

diane

[Alchemist]

I think Havanese dogs are descended from a very small number of individuals.

 

From http://www.dogbreedinfo.com/havanese.htm:

 

"A US breeder, Mrs. Goodale saved the breed from extinction. She advertised in the Florida paper, and found two or three immigrant families who had brought their Havanese from Cuba with papers. From them Mrs. Goodale got 6 Bichon Havanese with pedigrees; a bitch with 4 female pups, and a young unrelated male. Later she was able to get 5 more males from Costa Rica. As an experienced breeder, Mrs. Goodale began working with the 11 dogs."

 

I don't know enough about them to know whether they suffer from health issues.

 

Not canids, but aren't cheetahs all remarkably similar (genetically speaking)? I seem to recall that genetically they're all virtually identical - much more so than, say, the average housecat. And doesn't this contribute to the low fertility of cheetahs?

[Liz P]

I don't know, but the number of past ancestors doesn't matter so much as the coefficient of inbreeding (COI). The COI tells you how related two dogs are, or about how many genes they have in common.

 

The average COI for most ISDS registered BCs is about 6% to 7%. I know that many farmers try to keep the COI of their animals (cattle, sheep, pigs) below 3%.

 

I've heard there are purebred dogs with COIs equivalent to all the dogs within the breed being as closely related as littermate siblings. You must be able to get COI information for various breeds somewhere.

[Liz P]

Not canids, but aren't cheetahs all remarkably similar (genetically speaking)? I seem to recall that genetically they're all virtually identical - much more so than, say, the average housecat. And doesn't this contribute to the low fertility of cheetahs?

 

And a VERY low resistance to any infectious diseases.

[Pipedream Farm]

One of the studies cited as part of the BBC report on pure bred dogs in the UK examines the effective population of several breeds. I will find a link for this study later (or you can search the threads pedigree dogs exposed). Essentially, it determined from the UK's studbook the genetic diversity of several popular breeds and listed it as an effective population. These numbers of some breeds are on the order of 10's of dogs for all of the dogs in the UK studbook. IOW too little genetic diversity is BAD.

 

Mark

[Journey]

The average COI for most ISDS registered BCs is about 6% to 7%. I know that many farmers try to keep the COI of their animals (cattle, sheep, pigs) below 3%.

 

How did you find this number to be the average? Based on their comments in ISDN, they say that "average/normal" on peds below 3% and ones that have been published with a COI of 5 or higher they comment on as being "high". Many of their comments on COI's on the pedigree's say that "average/normal 1.4". In looking at the Irish/Scottish/Welsh/English team ped's and brace peds they are all below 2%.

[Liz P]

How did you find this number to be the average? Based on their comments in ISDN, they say that "average/normal" on peds below 3% and ones that have been published with a COI of 5 or higher they comment on as being "high". Many of their comments on COI's on the pedigree's say that "average/normal 1.4". In looking at the Irish/Scottish/Welsh/English team ped's and brace peds they are all below 2%.

 

I got that number from an article some years ago. Are you talking about the CI6 (coefficient of inbreeding for the most recent 6 generations) or the COI (coefficient of inbreeding for all ancestors)? It is very common for the CI6 to be below 2%.

 

ETA: Here is where I got my information.

[SoloRiver]

The number of ancestors is important because it affects how inbred the population is. However, in domestic animals the number of founders may actually overestimate present genetic diversity since certain animals (popular stud dogs) may be bred very often and other animals infrequently or not at all.

 

One modern breed that is probably comparable to the Isle Royale wolves is the Basenji. In the 1980s or 1990s some breeders went back to central Africa to get a handful more dogs (more info on the African Stock Project, which is fascinating, here) and actually succeeded in getting the AKC to register them despite the fact that they had no pedigree information in an effort to diversity the gene pool, but from what I was told (by a Basenji fancier who strongly supports the importation of more African dogs) only a few of them were used and many breeders avoid the "Avongara" lines (as the Africans were called) altogether because they have "poor breed type." The importation of the new African dogs introduced the brindle color to Basenjis, which some breeders consider to be proof of mongrelization. Most Basenjis suffer from Fanconi Syndrome.

 

I traveled to the Portuguese Water Dog national specialty in 2007 to sample dogs for the Canine Behavioral Genetics Project and was surprised to learn during a lecture there that the modern PWD in America is descended from something like only 10 dogs, maybe less. The breed was first imported to the U.S. in 1968 and has increased enormously in popularity since that time. Another very inbred breed, according to someone who has been in that breed long enough to be called a "dinosaur," is the modern (show) Bearded Collie, which in the United States descends from less than a dozen individuals imported as late as the 1960s. The effective population sizes of these and many other breeds are probably shockingly low.

 

Cheetahs are so genetically similar to each other that skin grafts between "unrelated" individuals are not rejected. They are thought to have undergone a relatively recent population bottleneck that was not human-caused (i.e., it happened in antiquity, before there were enough humans to have done it to them) and they're probably undergoing another one now that humans have more to do with. I expect that cheetahs will be extinct in the wild before the end of this century, not only because they are so susceptible to disease and have such low fertility, but because they are outcompeted by pretty much everything else in their environment, including other big cats like leopards (which are much more behaviorally adaptable), lions, and humans.

 

ETA: Here's a blog post tut-tutting the finds of the Isle Royale studies and the interpretations of, among others, our friend Terrierman.

[Liz P]

The number of ancestors is important because it affects how inbred the population is. However, in domestic animals the number of founders may actually overestimate present genetic diversity since certain animals (popular stud dogs) may be bred very often and other animals infrequently or not at all.

 

You summed it up better than I did when I said that the COI was more important info than the number of ancestors. You can have a lot of ancestors but a high COI thanks to popular sires.

[Mark Billadeau]

Here is the article I elluded to in previous posts.

 

Population Structure and Inbreeding From Pedigree Analysis of Purebred Dogs

 

Abstract

Dogs are of increasing interest as models for human diseases, and many canine population-association studies are beginning to emerge. The choice of breeds for such studies should be informed by a knowledge of factors such as inbreeding, genetic diversity, and population structure, which are likely to depend on breed-specific selective breeding patterns. To address the lack of such studies we have exploited one of the world's most extensive resources for canine population-genetics studies: the United Kingdom (UK) Kennel Club registration database. We chose 10 representative breeds and analyzed their pedigrees since electronic records were established around 1970, corresponding to about eight generations before present. We find extremely inbred dogs in each breed except the greyhound and estimate an inbreeding effective population size between 40 and 80 for all but 2 breeds. For all but 3 breeds, >90% of unique genetic variants are lost over six generations, indicating a dramatic effect of breeding patterns on genetic diversity. We introduce a novel index Ψ for measuring population structure directly from the pedigree and use it to identify subpopulations in several breeds. As well as informing the design of canine population genetics studies, our results have implications for breeding practices to enhance canine welfare.

 

Table 3 summarizes their results of the 10 breeds studied. For example, there were 31,259 Golden Retrievers in their data wih an effective population size of 67.

 

Mark

[Journey]

I got that number from an article some years ago. Are you talking about the CI6 (coefficient of inbreeding for the most recent 6 generations) or the COI (coefficient of inbreeding for all ancestors)? It is very common for the CI6 to be below 2%.

 

No your right Liz, it was the C16 listed in the ISDN not the COI, I quickly glanced and simply assumed....

[Ooky]

Thanks for posting, interesting stuff. It does not surprise me that the dog fancy would leap to the conclusion that inbreeding can be ok based on this study (since a lot of people seem to believe "well, what's good for wolves..." without further evidence or thought), but it has so little to do with their situation that it's actually pretty laughable.

 

1 - This is an inbred population also under a HEAVY (you might say ruthless) culling - and the culling is based on, among many things, ability to do very demanding work (on a very specific and demanding prey base) and ability to withstand disease. Neither of which conditions humans could create well or imo humanely (at least the way they are enacted on this population), but which are CERTAINLY not recreated in show bred dogs.

 

2 - this population has only been around for 70 years or so - basically no time at all in the longer term evolutionary history of the wolf species. This island may even be a population sink, when viewed in a longer term. But in any case, metapopulation theory would predict that many smaller populations, some which become isolated, wink into and out of existence over time. This process has nothing to do with artificial selection.