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Spread of Adaptation and Migration Load in a Spatially Structured Population
Nordstrom, Scott W.
Nordstrom, Scott W.
Abstract
Mercury contamination reduces fledging probability in birds. Mercury has been introduced to the South River in the Shenandoah, creating differences in habitat quality on a landscape of fragmented forest patches. To study the possible outcomes of the spread of this adaptation through populations in the Shenandoah, we construct and implement a mathematical model that features common life history traits, including dispersal and nest competition, of a generic bird species. To see which processes or parameters have the largest effect on allele frequencies, population sizes and reproductive output (a proxy for fitness), we use partial rank correlation. We conclude that in a simple two-patch instance of the model, local selection pressures and asymmetry of migration have the largest effects on allele frequencies and fitnesses. In half of cases observed, the mercury tolerance allele did not establish in either patch, but it did reach fixation in both patches in 20% of trials run. We also find that in a two-patch instance, allele frequencies in the contaminated and uncontaminated patches tend to correlate with each other very well, suggesting that there is a homogenizing process which couples allele frequencies.
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2015-04-01
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Biology