Diversity and geographic distribution of riboprints from three cosmopolitan species of Colpoda Muller (Ciliophora: Colpodea)

Ribosomal RNA gene restriction site polymorphisms were determined for 114 isolates of three cosmopolitanly distributed species of Colpoda, a common soil ciliate genus. Isolates were obtained from soil samples and identifications confirmed using silver staining techniques. Based on restriction site analysis of a 1095 bp region of the large subunit (LSU) rRNA gene, thirty-one distinct riboprints were observed; 11 unique to Colpoda steinii, 8 unique to Colpoda inflata, 10 unique to Colpoda cucullus, and two riboprints shared by several isolates of C. inflata and C. cucullus. The average intraspecific genetic distance estimated from riboprint data was greatest among C. steinii isolates (0.0790, n = 37), intermediate among C. cucullus isolates (0.0519, n = 37), and the least among C. inflata isolates (0.0383, n = 40). Phylogenetic analysis of riboprint data using distance methods revealed no geographic pattern in the distribution of riboprints in any of the species examined. Furthermore, many of the riboprints were globally distributed, suggesting no equatorial barrier to species dispersal in the species examined. Several riboprints, however, appeared to be restricted on the basis of temperature, suggesting the possibility of fitness differences among riboprints with respect to environmental variables. Shared riboprints between two species of Colpoda indicates the limitations of riboprints in species discrimination within in this group, possibly due to the retention of ancestral polymorphisms or the inadequate resolution of the region of LSU rRNA gene that we examined. Additional molecular markers will be needed in order to resolve this issue.