Waiting time to parapatric speciation

Using a weak migration and weak mutation approximation, I studied the avera ge waiting time to parapatric speciation. The description of reproductive i solation used is based on the classical Dobzhansky model and its recently p roposed multilocus generalizations. The dynamics of parapatric speciation a re modelled as a biased random walk performed by the average genetic distan ce between the residents and immigrants. If a small number of genetic chang es is sufficient for complete reproductive isolation, mutation and random g enetic drift alone can cause speciation on the time-scale of ten to 1000 ti mes the inverse of the mutation rate over a set of loci underlying reproduc tive isolation. Even relatively weak selection for local adaptation carl dr amatically decrease the waiting time to speciation. The actual duration of the parapatric speciation process (that is the duration of intermediate for ms in the actual transition to a stale of complete reproductive isolation) is shorter by orders of magnitude than the overall waiting lime to speciati on. For a wide range of parameter values, the actual duration of parapatric speciation is of the order of one over the mutation rate. In general, para patric speciation is expected to be triggered by changes in the environment .