These values theoretically bound the region between samples in which gene flow is less important than random genetic drift and those in which gene flow should be dominant, producing panmixis
. On the basis of the general relationship, these levels of gene flow were calculated to occur at dispersal times of 9 and 29 d, respectively.
[F.sub.ST], however, is based upon an infinite island model that assumes there are an infinite number of subpopulations (Wright 1931); [Theta] was derived to accommodate a finite number of populations and ranges from zero (complete panmixis
) to one (complete isolation, see Weir and Cockerham 1984).
For example, selection among divergent gene combinations fixed in different demes may allow the species to either adapt faster or reach a higher fitness peak than would be possible with panmixis
, regardless of whether divergence was due to drift (as postulated by the SBT) or to selection.
The net effect is to increase the effective population size of the mt-genome, when the species population as a whole is considered, because alternate haplotypes become locally fixed, resulting in the species population being more polymorphic than expected if there were specieswide panmixis
. Hoelzer argues, given that the effective population size of the mt-genome for the species is increased relative to that of a nuclear autosome, the probability of congruence of the mt-haplotype tree with the species tree should diminish relative to that of a nuclear autosome.
The rapid divergence permissable under the diffusion-modified Fisher process effectively acts as a temporal barrier to gene flow, with divergence at particular points in space occuring over a time scale well below that of panmixis
. This is because an increase in the preference for a given male corresponds to a reduction in the rate of diffusion of that male.
Third, in populations close to panmixis
, alleles at different loci are likely to show similar patterns of variation only if they are subject to similar selection pressures.
The intercept of the regression serves as an estimator of Wright's (1946) neighborhood size, or the number of individuals in an area of panmixis
(Slatkin and Maddison 1990; Slatkin 1993).
In most cases, a nonsignificant excess of heterozygotes was found (negative [F.sub.IS] values), indicating that populations simulate panmixis
. In TA as well as WMA the primary component of FIT was [F.sub.ST], whereas the [F.sub.IS] component was rather large in EMA.