1 Tahrcountry Musings: The reversal of genetic decline

Friday, March 04, 2011

The reversal of genetic decline

We constantly talk about isolated populations and genetic erosion.  Very little is known about the time-scale over which adverse genetic effects develop in natural populations. The other day I was discussing the subject with my friend Ramesh. Ramesh wanted to know whether genetic rescue of isolated populations is possible or not.

Yes, it is possible. We have a good example from National Bison Range of northwest Montana where Bighorn sheep from Alberta's Banff National Park started a new herd with the release of 12 animals. The herd grew rapidly, but soon peaked at 90 animals and ultimately stabilized at around 40. Genetic diversity of the insular group was very low, restricted to the limited gene pool of the dozen founding animals. For 11 generations the bottleneck continued, overwhelmed by deleterious genes.  Then wild sheep, totalling 15 animals, captured mainly from other Montana herds, were transplanted to National Bison Range over a period from 1985 to 1994. The migrants brought about dramatic changes to the herd's reproductive fitness. The herd's population growth rate reversed and was on the upswing again. The newly-contributed genes overshadowed the negative effects.

Yes, genetic principles deserve wider recognition as practical management tools.

Have a wonderful weekend. The next update will be on Tuesday

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