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In humans, there are various cultural rules to avoid inbreeding (to the level of paternal cousins, nieces/nephews and uncles/aunts etc)

How do animals such as dogs avoid the problem of inbreeding? They do not have a record of their relatives and there seem to be many siblings in each batch for some animals. How does it work in the wild or among stray animals? Is their DNA somewhat resilient to these genetic disorders?

Likewise, how do birds handle this issue?

EDIT: I am not trying to breed animals, want to understand how it works in the uncontrolled wild when the young leave home early and are scattered.

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  • $\begingroup$ Is it even a problem? Especially when you consider the Darwinian effects. That is, most animals produce far more offspring than needed to keep a stable population, so only the fittest survive to reproduce. ("Fittest" here being a rather circular definition, as an individual that survives is fit.) So if an instance of inbreeding produces unfit individuals, they don't survive. And at the extreme, with a limited population some inbreeding might be necessary for species survival. $\endgroup$
    – jamesqf
    Commented Jun 30, 2017 at 19:12
  • $\begingroup$ @jamesqf yes, I want to know if there is such a case observed in practice. It is known that cheetahs suffer from an inbreeding problem and the genetic makeup of any pair of cheetahs is currently too similar. How about other creatures? $\endgroup$
    – user1952500
    Commented Jun 30, 2017 at 19:15
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    $\begingroup$ @jamesqf Of course it's a problem. The very definition of "fitness" is based on progeny survival. Progeny represent a large energy investment, so there's should be (and is) strong selection to prevent individuals from generating large numbers of unfit offspring. As the answer shows, there are in fact multiple mechanisms to prevent inbreeding, so observation supports theory. $\endgroup$
    – iayork
    Commented Jun 30, 2017 at 19:16
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    $\begingroup$ @user1952500 There are widespread claims that cheetahs suffer from inbreeding problems but they're not well supported. It's clear that cheetahs are inbred, but very little evidence that it affects their reproductive efficiency. There are well-understood mechanisms by which inbreeding effects can be minimized (flushing of deleterious alleles) and it's likely that cheetahs went through those. $\endgroup$
    – iayork
    Commented Jun 30, 2017 at 19:19
  • $\begingroup$ @iayork: That was my point, that there does not seem to be any significant adverse effects from occasional inbreeding. Based on my (admittedly limited & unscientific) observation of animals & humans, I'm not entirely convinced that there really are effective prevention mechanisms other than dispersal, which of course has more obvious benefits. Certainly among humans, avoidance of inbreeding seems to be more cultural than biological. There are examples of cultures, like ancient Egypt, where it seems to have been common, at least among royalty. $\endgroup$
    – jamesqf
    Commented Jul 2, 2017 at 18:34

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The question is interesting. However, it will be impossible to answer accurately for all birds as the mechanisms actually used vary from species to species. So I will give you some information in the general sense.

Recurrent inbreeding reduces inbreeding depression

Inbreeding depression is caused by both

  1. Recessive deleterious alleles that are brought to homozygosity
  2. Some epistatic interaction

In any case, in a population where inbreeding is common, those recessive deleterious alleles and alleles involves in these deleterious epistatic combinations will be washed out (or at least brought to lower frequency) of the population via selection and the population will end up suffering less from inbreeding than a typical outbreeding population. In the extreme, a population of exclusively selfer individuals, such deleterious recessive alleles are brought to extremely low frequency within lineages.

How to avoid inbreeding?

Now, sure animals and plants typically don't have a big book that allow them to tell how related they are to another individual. However, there are other mechanisms of kin detection

Self-incompatibility

For example, in plants self-incompatibility is thought to be relatively uncommon. There exist many mechanism, so I-ll just consider a simple example. Consider a self-incompatibility locus as a specific loci for which if the same allele is shared by both the pollen and the ovule, then no fertilization occurs. This prevents selfing and prevents mating with many of the closely related mechanisms.

Body odour and sexual attraction

Also, there are mechanism that can mediate sexual attraction toward individuals that differ. The classical example is Major histocompatibility complex (MHC) and sexual attraction (vertebrates), where individuals tend to be attracted to individuals that have a different MHC.

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  • $\begingroup$ I was just curious about dogs because I have seen stray dogs in large numbers in some countries and wondered how they would handle it. I have not seen that many stray cats or other animals. There have been many wild birds as well, hence asked about them. They could apply to any animal in general. $\endgroup$
    – user1952500
    Commented Jun 30, 2017 at 17:22
  • $\begingroup$ I didn't downvote, but would encourage you not to use the terrible, terrible "research" that claims to show MHC compatibility effects in humans -- the so-called experiments are an embarrassment that showcase virtually every bad research practice there is. $\endgroup$
    – iayork
    Commented Jun 30, 2017 at 17:25
  • $\begingroup$ @iayork I did not read that paper. I only went to the conclusion. I did not know, their experimental design was considered so bad. I removed the reference (and the associated claim) and will read the paper to make my own opinion on it. Thanks $\endgroup$
    – Remi.b
    Commented Jun 30, 2017 at 17:29
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The term you are looking for is Kin Detection. which is the methods of recognizing related organisms, important both for avoiding inbreeding and aiding relatives.

There are several known mechanisms.

First they can avoid it the same way humans, they don't want to mate with anyone they were raised with. Humans don't need an understanding of genealogical to avoid mating with kin. Humans have an aversion to to romance with anyone they shared meals with frequently as a child. It is called the Westermarck effect or sometimes reverse imprinting and is part of humans in built kin detection system. It can work with many method just by building a brain that sees those who were around when you were a child as likely kin and thus unattractive to downright sexually repulsive. It is not perfect, it can be confused by adoption or separation, but works fairly well in the natural human setting. in effect their "record" is simply their memory.

Smell is another known method, in animals with better senses of smell than humans can detect certain factors that would indicate relatedness, like genetically controlled urinary proteins or simply smells of familiar and thus likely related individuals. This can work hand in hand with the Westermarck effect. There is even some very preliminary evidence humans may use this method to some extent.

Basic dispersal patterns can also do this by behaviorally programming one sex to travel far from where they are born and the other to not do this, it decreases the chance they will end up mating with a relative.

Now the formalized study of inbreeding avoidance is relatively new, mostly due to the technology making detecting kin for the scientists easier being new, so more and more research will almost certainly find other methods as well.

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