Inbreeding Depression?

With only three founders, there is some question as to whether the McBride lineage is suffering inbreeding depression. Inbreeding depression results from the expression of deleterious recessive alleles which are normally present only in the heterozygous condition. Because these alleles are harmful and lower the fitness of any individual who expresses them, they are vary rarely seen in the homozygous state (or at all) in the genepool of normal populations. However if a genepool is severely inbred and the members of that pool carry a lethal recessive allele, the chances of that allele being present in the homozygous condition in any individual are much greater. Phil Hedrick and Phil Miller have run a genetic analysis to confirm the fact that there are in fact three founders and to test whether or not inbreeding depression has become a problem.

There has been some argument in the past over weather wolf #2 is a fourth founder or the son of founder wolf #5 (a female). Hedrick and Miller found that #2 shares an allele with #5 in each of sixteen unlinked polymorphic microsattelite loci and that #2 shares two alleles with three putative siblings (which are the progeny of #5) in fifteen of the sixteen loci. While this is very compelling evidence that #2 is the son of #5, it is still possible that #2 could have received a unique set of alleles from his father. However, Hedrick and Miller have found similar alleles in #2 and #7, 8 and 9, all of which are the progeny of founder wolf P5. If #2 were not the son of #5 and P5, all of these results would be extremely unlikely.

Given that there are only three founders, the inbreeding coefficients of most individuals will be fairly high and there is some cause for concern over inbreeding depression. Hedrick and Miller tested for inbreeding depression by comparing juvenile survivability across a gradient of inbreeding coefficients. Here are their findings:

The results do not indicate any significant inbreeding depression. However it is important to note that because of the small sample size and relatively short amount of time spent inbreeding, there could be important inbreeding depression in this population. This particular test just may not be sensitive enough to detect it yet.

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