VARIATION IN THE RIBOSOMAL INTERNAL TRANSCRIBED SPACERS (ITS1 AND ITS2) AMONG 8 TAXA OF THE MIMULUS-GUTTATUS SPECIES COMPLEX

The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA sequence and the intervening 5.8S region were se quenced from three individuals in each of eight taxa of the Mimulus gu ttatus species complex. Three discrete variants, or ''types,'' of ITS sequences were found, among which 30%-40% of sites differed, compared with 1%-2% within types. Dot plots indicate that these types were not related by conspicuous rearrangements or inversions. More than one ITS type was often found in the same taxon, and two of three ITS types sp an species boundaries, indicating their presence prior to speciation. These ITS sequences showed essentially no positional homology with the nearest sequenced relative, tomato. In contrast, the 5.8S region was relatively unvaried, with 8 of 162 sites varied in the sample among al l eight taxa. The phylogeny inferred by the most common ITS sequence t ype, rooted by the two other ITS types, agreed with isozymes in showin g the distinctness of M. nudatus, M. laciniatus, and M. tilingii from the other five taxa.