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It's been discovered that female guppies - which practice polyandry (taking multiple mates) - have a mechanism by which they can slow down the sperm of closely-related mates. Amazing!
"It's new and interesting," said Bob Montgomerie, an evolutionary biologist at Queen's University in Ontario, Canada, who was not involved in the research. "If females can prevent fertilization by a close relative, they aren't wasting energy forming a zygote that will likely die due to the accumulation of harmful mutations."
Researchers have long suspected that polyandry evolved in some species as a strategy to reduce breeding with relatives, but lack of evidence for how the females bias paternity after mating has caused the hypothesis to remain simply that.
It's a wierd concept to some dog breeders who have grown up to believe that inbreeding is a good thing but there is a wealth of evidence that the females of many species avoid mating with close relatives. Dog breeders also often try to justify inbreeding by swearing blind that male wolves inevitably mate with their daughters - but this simply isn't true. There's evidence that all wild canids avoid inbreeding. And although they will mate with relatives if there's no option, it appears some at least have the ability to limit the damage. A study of an isolated population of wolves on the Swedish peninsula found that females were somehow able to choose mates that were, genetically, the least related even if, on paper, they were similarly related (Report on Science Daily).
Wild African dogs also practice inbreeding avoidance. A study of a single population in Kruger National Park showed that male and female wild dogs that formed new packs did so only with unrelated members of the opposite sex (Girman et al). This was true even though most males and females dispersed to territories very near their close relatives. Indeed, the researchers found no evidence for inbreeding in the Kruger population.
The domestic dog, however, appears to have, largely, lost this ability - bred out of them by artificial selection imposed on them by us. For every story of a bitch turning her nose up at a brother or father's amorous advances, there is another of one absolutely determined to keep it in the family.
Of course, that doesn't make it right...
Jemima, this is your best post yet!
ReplyDeleteI still say, we could learn a lot from the cat fancy. The major purebred cat registries (at leas in the U.S.) allow outcrossing of various kinds (for health reasons, etc) and it's not considered a big deal. As long as a cat looks and acts like it's breed and has a few generations pure pedigree behind it, it can be added to the main studbook as pure.
ReplyDeleteOne only has to look at examples like the Boxer Outcross and Dalmatian Outcross projects to see how it does not mean the end of purebred dogs or correct type to allow intelligent outcrossing once in a while.
In this modern age, where we rarely have the huge mega-kennels of 50-100 years ago where breeders had their pick of genetic material to use, the modern small scale 'hobby breeder' situation has really reduced the genepool in many breeds. A closed studbook is not viable for many breeds nowadays, if they wish to survive into the next 100 years; inbreeding depression will eventually lead to their extinction.
Don't forget the intelligence of petunias!
ReplyDeletehttp://www.eurekalert.org/pub_releases/2010-11/ps-tpi110110.php
There is an interesting account of a husky bitch that refused to mate with two of her male offspring that grew up in the same house with her, but when one who had grown up in a different house showed up while she was in season, she assumed the position and would have mated had the owners not intervened.
ReplyDeleteIt is in Elizabeth Marshall Thomas's The Hidden Life of Dogs-- a book that I've always found interesting. However, it must be taken with a grain of salt because she applied ethnography methodology to the behavior of her pack of huskies, a dingo, and a pug. She talks about how her husky bitch became so strongly pair-bonded to a male husky that she refused all suitors until he came around. Of course, all suitors meant a male pug that lived in the house with her, and some large bitches won't mate with small dogs or even show any interest.
(She also let her male husky wander the streets of Cambridge, Massachusetts, which is a hard enough place for pedestrians to navigate, much less a dog. She got some deserved criticism for that.)
The reason why domestic bitches may be less inbreeding adverse may have to do with the simple fact that female dogs are much more likely than wolves to respond to courtship signals that any given male dog will give off. Stanley Coren writes about this in How to Speak Dog in which he quotes the wolf literature on how often wolf bitches respond to the courtship signals of their pair-bonded mate and compares that to the way domestic bitches mate with whatever shows up and gives off the signal.
ReplyDeleteDogs do not--in general-- pair bond, and although wolves and other wild dogs are not strictly monogamous, their whole pup raising system is based upon a dog and bitch that are pair-bonded. (In red foxes, this isn't always the case. Dog foxes often mate with several vixens that are forced to raise their kits on their own.) In wolves, the pair-bonded pup raising system includes adults (usually relatives) that then are useful in pursuit of large species. Because dogs do not typically have pair-bonding as the basis of their social structure, it is more efficient from a gene-centered perspective to mate with the first dog coming along.
And just to have a glance at a completely different scenario.....here's a link to what is considered the oldest and most intensely inbred family of animals in the UK, the famous white Chillingham cattle herd. Interestingly it is agreed that the herd is greater in number and hardier than ever before.
ReplyDeletehttp://northeast.greatbritishlife.co.uk/article/north-east-life-wildlife-wild-cattle-chillingham-alnwick-belford-thomas-bewick-18778/
Yep, the Chillingham herd is an exception - and of course there are others examples of inbred populations that appear to have purged their deleterious genes. But they are an exception rather than the rule and that's why they are so fascinating to geneticists. And you can't compare them to dogs for one very important reason: natural selection is operating in this wild herd. The males spar and have to earn the right to reproduce and this helps a lot in terms of perpetuating fitness. The Chillingham herd is still very vulnerable though. If WE were all as genetically similar as they are, the Black Death could have wiped out every human on the planet, not just million, because there would have been no variety of response to the virus, as there is in a genetically diverse population.
ReplyDeleteIt should also be noted that the selection process that most domestic dogs go through is not equivalent to anything like natural selection. Some dog breeding theorists-- like Lloyd Brackett-- thought that humans could select healthier and healthier dogs. Unfortunately, we humans are not as good as nature is at selecting against disease and defect, and that is one reason why we have to be careful in inbreeding.
ReplyDeleteSome working dog breeders in the US do breed very tightly, but they make their bitches whelp outside in steel barrels. A pup whelped out in a steel barrel in winters is born under harsher conditions than any wolf or coyote. If any defects exist, the pup is culled.
Of course, not many breeders would be willing to do this, and if one is breeding for conformation, it would be a mistake-- some of "the best" puppies could be culled.
All of these populations of inbred animals that are doing well need to be taken with a grain of salt. Yes, they may be doing well. Maybe natural selection has culled out the deleterious recessives. Maybe the animals are able to cope with pathogens with just a little MHC diversity.
However, as we have seen with Tasmanisn devils, things can be going well, and then they sudden come down with that bizarre transmissible cancer, which could easily make them go extinct.
I also remember that it wasn't long ago that people were bragging about how healthy and long-lived golden retrievers were. I have several breed books from the 1970's that make this claim, and now the average lifespan of the breed in the US is about 10 years. This breed has real issues with most-used sires.
So animals can appear to do well with reduced genetic diversity-- and that's all nice and well, until the animals don't. And then it's often too late to solve the problem.
Because of these risks, inbreeding is not an ideal practice.
Whelping puppies in steel barrels? Is this a respectable practise or grounds for RSPCA intervention? I sort of get the theory, but don't see how future anomalies such as cataract or HD would manifest themselves in puppies too weak to pass that grueling test.
ReplyDeleteMy comments re: the Chillingham herd was not an endorsement of inbreeding, just another piece of interesting info.
I also agree that this sort of intense inbreeding is not an ideal practise longterm....however in 30 years of dog breeding, during which I have seen the results of linebreeding and total outcrossing (in both dogs and cattle), I have yet to see any method that yields the 100% success rate you guys seem to be making the public believe is possible.
I don't think anyone here has suggested that a change in practice will yield a 100 per cent success rate. Of course it won't. We are dealing with living things here, every individual carries dodgy genes and getting rid of them all would very likely be a mistake. Genes are not discrete entities; not either pantomime goodies or baddies.The reality is much messier than that. They often code for many traits, good and bad. Eg the gene for sickle cell anaemia in humans confers some protection against malaria.
ReplyDeleteI should make it clear that I am an American, so the RSPCA has not authority over me in any fashion.
ReplyDeleteThat said, it is standard practice for foxhounds and coonhounds in this country to be bred in this fashion. The dogs are usually pretty tightly bred, and in coohounds, because they have definite trial culture, there are popular sire issues. The breeding outside in barrels is standard procedure. The weather conditions do select away from weakness, though not from those particular disorders. They do hold off issues like an inbreeding depression. Someone pointed me to an American breeder of working Airedales, who breeds very closely (half brother to sister matings) and the pups are whelped outside. The dogs are generally healthy, but only because any weak puppies die. It is very similar to the process that made it possible for cheetahs to survive their severe genetic bottleneck.
(BTW, coonhound is the politically correct name for those dogs. They are all registered as coonhounds.)
It is unfair to make comparisons with dogs and those cattle for very simple reasons 1. Natural selection has taken out most of the deleterious recessives and the cattle have managed not to experience an inbreeding depression. 2. Cattle are harem breeders and have a natural history in which they have evolved from ancestors that typically are produced from just a few breeding males.
Dogs don't have any of those characteristics. If you inbreed dogs, you are very likely to experience an inbreeding depression before the deleterious recessive can be bred out-- if they can at all, because humans are terrible at selecting out these genes without exposing others. Secondly, dogs are derived from ancestors that pair bond, which means more males produce the offspring. And in wolf packs that have multiple breeding females, the extra females normally mate with outsiders (Casanova wolves). All of these ensure that wolves have great genetic diversity-- and historically have had remarkable genetic diversity. However, the wolf and dog species, Canis lupus, has not evolved any kind of inbreeding tolerance. Cattle have a lot more inbreeding tolerance, simply because they are harem breeders. The same goes with rodents and lagomorphs.
Here's a really good analysis of why we have to be careful when making comparisons about inbreeding across species:
ReplyDeletehttp://desertwindhounds.blogspot.com/2010/12/closed-registries-dogs-in-handbasket-to.html
Wow... that is a fantastic link and I hadn't seen it before. Thank you so much for posting. Thank you too for the info re harem breeders - I didn't know they had more inbreeding tolerance.
ReplyDeleteJemima, if you think Chillingham herd is not a good example, how about Thai Ridgeback? Thai Ridgebacks are purebred dogs and they did have natural and selective breeding in the past. it's shown that inbreeding does not digress these species at all. I always believe that inbreeding is just one of breeding tools. If used properly, it can improve things, if used improperly, it can make things worse.
ReplyDeleteInbreeding is never adaptive in species that reproduce sexually. The entire point of sexual reproduction is to find mates that are genetically diverse, to produce heterogeneous offspring that can adapt to the environment. ALL species that reproduce sexually have a deep biological aversion to inbreeding, just the way humans do. In a small, restricted population, animals will inbreed as a last resort, because offspring with vulnerable immune systems are at least better than no offspring at all. In that sense, if a single breeder and her dogs were the sole survivors of some apocalyptic disaster, and there were no other dogs available for her dogs to mate with, then inbreeding would be the tool to use as a last resort to preserve the species.
ReplyDeleteBut even in a restricted population, animals -- humans included -- deliberately choose mates whose MHC profile differs from their own. We do this by scent. Body odor is the phenotype, the outward physical manifestation, of the genetic code that determines MHC. This is why people we are attracted to smell so heavenly: it's nature's way of saying 'go ahead! make a baby!' because that baby will have a strong immune system and therefore a good chance of surviving. This is how the isolated population of foxes mentioned in the linked article was able to maintain diversity in their MHC profiles, even in such a small, homogeneous population: they can sniff out the ideal mate whose immunities are different from their own.
No wonder dogs spend so much time sniffing each other!
The narrower the gene pool the better. Doris Lan is correct. It depends how its managed. Fact is there's a lot of rot talked about inbreeding (which highlights pre-existing conditions rather than creating new ones; anyway my alarm always goes off when I see the word 'diversity'). Take a butcher's at this if you haven't all ready.
ReplyDeletehttp://www.theokaa.org/articles/inbreeding.pdf
I had to read with my fingers to follow it all but I dare say you're all much brighter than me and likely to get the gist of it pretty quickly. A contribution to the debate of nothing else.
Clearly Thea is a product of the university brainwashing machine - full of certainty, perhaps some of it related to the way things actually work. It's possible the history and the anthroplogy they fed me was a pack of lies. On the other hand a little cross-cultural work plus a considered glance at, say, pharonic Egypt (where they produced leaders of genius and strikingly few babbling idiots) and 'All species that reproduce sexually have a biological aversion to inbreeding' begins to look a bit strong.
That's great, Anon 10:31. Let's take King Tutankhamun as an example of that theory. He was the product of a full brother and sister couple, as proved by DNA analysis. CT scans on his mummy have shown that he suffered from scoliosis, a cleft palate, a crippling bone disease which researchers believe may have necessitated the use of a cane to walk with (in fact a supply of canes were found in his tomb to supply him for the afterlife), and the research points to various other illnesses as well including sickle cell disease. There is evidence too that Marfan's syndrome ran in the family. Tut's eventual death at about 18 years old was due to a severe fracture of his leg which failed to heal and caused fatal complications; this coupled with severe recurrent malaria. This points immediately to lack of vitality, commonly seen when inbreeding is practiced to an extreme extent.
ReplyDeleteIn keeping with this tradition, he married his half-sister. They conceived 2 daughters together which were found mummified as foetuses in Tut's tomb. That is to say they did not survive to term and were miscarried. Tut and his wife did not manage to produce any live offspring. We cannot know how many other miscarriages she may have had. We do however know that loss of fertility is a well-documented direct consequence of inbreeding. Also, it is known that foetuses with genetic defects are far more likely to be rejected by the body and miscarried. Genetic defects and deleterious mutations do occur more frequently when inbreeding is severe.
The comment that this system "produced strikingly few babbling idiots" is also a red herring. The intelligence or otherwise of any given Pharaoh can hardly be judged objectively. The evidence we have is limited to what they left in their tombs, and whatever monuments were built in their name. Bear in mind that these Pharaohs did not personally build and design these monuments. They merely commissioned skilled architects and engineers to design them, then put their names to them when they were built. They had advisors and politicians to guide their decisions. Bear in mind as well that whatever written evidence we have of these Pharaohs will have been in the form of propaganda, will have been subject to editing and obliteration by later kings who disagreed with them, and will be clouded by the fact that their religious belief system actually had them as gods on earth. There was no way anyone was going to point out that the current incarnation of the great god Amun was mentally deficient. This would be tantamount to blasphemy.
I was going to comment on the article you have linked to but I fear my remarks may make this post unsuitable for publication because of the absurdity of the whole thing.