Inbreeding (would really like an informed debate)

[MadHatter]

Tintola: With the "Island Syndrome" it is important to keep in mind that the evolution of a genetically diverse population occurs over a span of thousands, if not millions of years.
In each case the population will go though what is known as a "Genetic Bottleneck" in which the population suffers inbreeding depression while the deleterious allelles (genes) are bred out of the population. On an island, where there are few or no natural predators and novel diseases, a population will have a higher chance of surviving this period of low recruitment. If the population survives this (and it's fair to assume that the vast majority do not) the genetic diversity of the population will slowly be re-built through natural mutation.
The time scales involved are many, many times the span of a human lifetime, so it can hardly be expected to occur over a few generations of captivity.

[Diane]

Sibling to sibling resulted in increased size in the Mendel case.
Genetic Bottleneck and inbreeding depression also results in diminished fertility and length of life.
This makes me wonder about budgie breeding.
As budgies seem to be getting larger and larger these days does this mean a lot of inbreeding on in budgie breeding? I know that artificial insemination of budgie hens is possible and is practiced. Whether this speaks to the lack of fertility or willingness of the doner birds or human intervention in wanting more young from a given sire (there is that spectre of the show cage) is debatable.

[MadHatter]

If I had to hazard a guess, I would say that the increased body size in the Mendel case was an example of genetic drift or some kind of natural selection in which larger individuals had a competitive advantage over their litter mates - perhaps in gaining access to food resources.
The increase in body size in budgies is, I am quite sure, entirely attributable to artificial selection for this 'desirable' trait.

[Tiaris]

I don't at all doubt that the island theory & intentional inbreeding of rats to minimise recessive gentic problems are very valid but only where you are starting with a genetically robust population base of source birds/animals. I have heard others argue the case for the rabbit theory, sparrow theory and others for reviving scarce captive species but I only believe that a narrow genetic base has some possibility of re-establishment where the subject species is not already subject to decline largely as a result of lack of genetic variability (which is usually already the case with rarer captive species). In a nutshell, I only think that inbreeding is acceptable and viable for species which are already genetically robust, abundant and prolific. Anything less than this is a danger to intentionally play with for more than an occasional one-off.

[Weaver]

I am sorry but most of the buying and selling involves siblings; other than the larger breeders most people only have one pair so the offspring are obviously related. Many birds such as Gouldians are breed in colonys and again the offsping will tend to come from the dominant pairs and again will be closly related.
Many of us have had the same flock of birds for more than 20 years, retaining the best of the young ones and only adding new blood every few years.
We need to be mindful of the dangers of inbreeding but we shouldn't get paranoid either.
My focus is on the rarer finches and without inbreeding we will loose them forever. It can be done successfully as long as we practise it correctly.

[arthur]

Dybowski's from what I can gather (that's if there are any still available) are showing all the signs of the problems associated with a limited gene pool

Problems with other rare species occur from time to time but are sometimes Not For Publication as the breeder fears being labelled as having a weak 'strain'

[maz]

[quote="bluebutterfly213"]
I think parent and youngster pairing is ok, if a specific trait is wanted and other sources had been considered first, as long as the young produced from that pairing will be paired with a bird from a totally different source.
I wouldn't like to do sibling pairings. Bear in mind that my previous frame of reference regarding breeding was the dog show ring and this kind of pairing would have been frowned upon.
But having said that Gregor Mendel, is supposed to have bred mice, brother to sister for 40 generations without any noticeable difference except the increase in size. But, as we all know mice are a resistant species.
[quote]

This is an aspect of inbreeding that people often misunderstand the inbreeding coefficient for a parent offspring mating is actually the same as siblings.....aunts uncles etc are lower but still quite high.

[Diane]

I knew this would come up.

I understand that, as you have said, parent to young pairing, and sibling to sibling is the same co efficient = they both have 50% identical genetics.
But, and for me this is the big but and why I prefer not to go the sibling to sibling route.
For the sibling pairing the 50% identical genetics works on sliding scale, it could be as high as 100% or as low as 0.
With parent to young its an automatic 50%.
There is also the fact to consider that we are not dealing with a highly resistant species here either.

In mice or rats I don't think this would be a problem, as you said in your first post, the are highly resistant, but with my birds I prefer to err on the side of caution. Knowledge of what has already been done to the Blue Gouldian by indiscriminate breeding should be enough for any gouldian breeder to thoroughly consider pairings.

From what I have read, it seems unless you are into genetics in a big way, i.e studying them or already a geneticist, a lot of the time the terms "in breeding" and "line breeding" are just semantics, its just where you are comfortable drawing the line as to what you would or wouldn't do when pairing up related animals.

[E Orix]

Why the topic of inbreeding is generally treated as a NO NO
This topic has generally been hushed up for the last 50 years that I can remember.
Why!!! simply to stop it being accepted as a normal practice in particularly from the novice or
general bird breeder.
In the program of an experienced breeder who know what to do properly and maintain records it is an
important method.
Hopefully,the general opinion we currently have is to frown upon the practice which is great for our hobby
and believe me assisted our birds.
There are enough people out there doing the wrong thing already without relaxing our current opinions.
Don't inbreed and on the surface keep it as a NO NO.
On a personal note,
In my collection I have a number of Jacarinis Finches, my original pair were given to me by Erny Reed in the early1960's also around that same time I got my Yellow Faced Stars.
Today both species are still doing well,no sign of size deterioration,no mutations just the same. I can't imagine how many young I have put back into other collections. What I have done is simple and works for me. I add new birds frequenty but only male birds. By doing this the new bird has to mate with one of my females and I also know how old my females are as they are not as robust as a male.

[Tiaris]

Dybowskis are totally finished due to the lack of sufficient original genetic material as are a few other species. I understand that with some rarer species the simple fact is that distantly unrelated pairing options are simply not available so some degree of inbreeding is unavoidable if we are to keep them ticking over. Equally valid is that some now very rare species are in genetic meltdown & face imminent extinction from aviculture due to this multi-generational inbreeding over the past decade or so. The Green Strawberry finch is the perfect example of this - up to about 15 years ago they were held in sufficient numbers & showed sufficient genetic strength to sustain regular multi-clutching by many pairs with excellent health, fertility, clutch sizes & juvenile survival. The fact that only 1 breeder in the country has bred them with any degree of consistency over the past decade (& hence been the sole source of young breeding age birds) has resulted in the total collapse of the species in terms of physical vigour, fertility and juvenile survival rates. Inbreeding can only be taken to a certain point without the introduction of new blood. My over-riding point is that intentional mating of any species to closely related stock over more than one generation is very justafiably a no no when unrelated mating options exist. Sure many small scale breeders only have young birds from one pair but even when this is not the case I always find it useful to assume that birds from each breeder are all related & require alternate sourced extras for sufficiently unrelated pairs to be made up.