Inbreeding Depression in Metapopulations: Epistasis and Purging

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This research investigates the contribution of gene interactions to inbreeding depression, the decline in viability and reproduction that affects the offspring of close genetic relatives. Over many generations, inbreeding depression can be mitigated or "purged" as natural selection removes deleterious genes and gene combinations from inbreeding populations. Using a combination of theory and experiment, with flour beetles as the model system, this research investigates the rate of inbreeding depression and the rate of purging for single genes and gene combinations. Conservation strategies for managing the genetics of endangered species use elaborate pedigrees designed to minimize inbreeding depression. Because they mitigate inbreeding, they necessarily mitigate purging. These management strategies are based upon single-gene theory. When inbreeding depression is caused by gene interactions, it can accumulate faster or slower than expected from single-gene theory. Thus, current conservation practice might be either overly elaborate or hopelessly inadequate for its goal of minimizing inbreeding depression. In addition, a balance between inbreeding and purging might represent the best strategy in the long run. With gene interactions, purging by selection removes groups of deleterious interacting genes and be much faster than the rate predicted by single-gene theory, where genes are removed independently, one at a time.