Abstract
For a beneficial allele which enters a large unstructured population and
eventually goes to fixation, it is known that the time to fixation is
approximately $2łog(\alpha)/\alpha$ for a large selection coefficent $\alpha$.
In the presence of spatial structure with migration between colonies we detect
various regimes of the migration rate $\mu$ for which the fixation times have
different asymptotics as $ınfty$. If $\mu$ is of order $\alpha$,
the allele fixes (as in the spatially unstructured case) in time $\sim
2łog(\alpha)/\alpha$. If $\mu$ is of order $\alpha^p, 0p 1$, the
fixation time is $(2 + (1-p)d) łog(\alpha)/\alpha$, where $d$ is the
maximum of the migration steps that are required from the colony where the
beneficial allele entered to any other colony. If $= 1/łog(\alpha)$, the
fixation time is $(2+S)łog(\alpha)/\alpha$, where $S$ is a random time in
a simple epidemic model. The main idea for our analysis is to combine a new
moment dual for the process conditioned to fixation with the time reversal in
equilibrium of a spatial version of Neuhauser and Krone's ancestral selection
graph.
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