Evidence for limited intercontinental gene flow in the cosmopolitan mushroom, Schizophyllum commune

The genetic structure of populations of Schizophyllum commune was inferred from electrophoretic variation among 136 individuals at 11 polymorphic allo zyme loci to determine the extent of geographic differentiation in this wid espread mushroom species. The majority of the genetic variation was contain ed within populations; however, considerable genetic differentiation was ob served among populations (global G(ST) = 0.214). Clustering analysis demons trated that genetic distance was correlated with geographic distance and th at a large component of the genetic variation was due to allele frequency d ifferences among populations from the eastern and western hemispheres. Our results also suggest that populations are large and geographically widespre ad. The lack of fixed genetic differences among intercontinental population s at any of the allozyme loci suggests that long-distance spore dispersal m ay counter the effects of genetic drift in this cosmopolitan species. These results are contrasted with a previous description of the same collection, in which the mating allele distribution of the species displayed no popula tion substructure at any geographic scale (Raper et al. 1958). Broader impl ications of this study are that both species and mating allele distribution s may not be correlated with long-distance gene flow in basidiomycete fungi .