Ty. James et al., Polymorphism at the ribosomal DNA spacers and its relation to breeding structure of the widespread mushroom Schizophyllum commune, GENETICS, 157(1), 2001, pp. 149-161
The common split-gilled mushroom Schizophyllum commune is found throughout
the world on woody substrates. This study. addresses the dispersal and popu
lation structure of this fungal species by, studying the phylogeny and evol
utionary dynamics of ribosomal DNA (rDNA) spacer regions. Extensive samplin
g (N = 195) of sequences of the intergenic spacer region (IGS1) revealed a
large number of unique haplotypes (n = 143). The phylogeny of these IGS1 se
quences revealed strong geographic patter ns and supported three evolutiona
rily distinct lineages within the global population. The same three geograp
hic lineages were found in phylogenetic analysis of both other I DNA spacer
regions (IGS2 and ITS). However, nested clade analysis of the IGS1 phyloge
ny suggested the population structure of S. commune has undergone recent ch
anges, such as a long distance colonization of western North America fr-om
Europe as well as a recent range expansion in the Caribbean. Among all spac
er regions, variation in length and nucleotide sequence was observed betwee
n but not within the tandem rDNA repeats (arrays). This pattern is consiste
nt with strong within-array and weak among-array homogenizing forces. We pr
esent evidence for the suppression of recombination between rDNA arrays on
homologous chromosomes that may account for this pattern of concerted evolu
tion.