Abstract
We study the stepping stone model on the two-dimensional torus. We
prove several new hitting time results for random walks from which we derive
some simple approximation formulas for the homozygosity in the stepping
stone model as a function of the separation of the colonies and for Wright’s
genetic distance F ST . These results confirm a result of Crow and Aoki (1984)
found by simulation: in the usual biological range of parameters F ST grows
like the log of the number of colonies. In the other direction, our formulas
show that there is significant spatial structure in parts of parameter space
where Maruyama and Nei (1971) and Slatkin and Barton (1989) have called
the stepping model “effectively panmictic.”
Errata: off by a factor of 2 in def'n of $\alpha$ in Thm 5
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