Sibling Species within Paramecium jenningsi Revealed by PCR-RFLP

Paramecium jenningsi Diller et Earl, 1958 is classified in the so-called “aurelia” subgroup. The original assumption of the monomorphic status of P. jenningsi (Sonneborn 1970) has been repeatedly challenged over the years with the application of increasingly sophisticated methods and knowledge of the geographic distribution of particular strains of this species. Investigations concerning genetic polymorphism suggested the existence of two sibling species in P. jenningsi, comprised of strains inhabiting India, Saudi Arabia, China and Japan. In order to confirm the existence of these sibling species, here we apply the PCR-RFLP method for analysis of a fragment of the hsp70 gene coding for the Hsp70 cytosol heat shock protein. PCR-RFLP with enzymes Alu1I and EcoRI did not reveal size polymorphism of restriction fragments. Band patterns obtained with enzyme Tru1I showed variation corresponding to genetic polymorphism and were subject to comparative analysis using the BIO1D program which applies Nei and Li’s and Jaccard’s similarity coefficients. The results of these analyses are homology trees showing the genetic similarity between West-Central Asian and Japanese groups, the intra-group similarity coefficients had a value of 1, i.e. the strains were 100% homologous. The similarity between both of these groups was calculated as 32% and 20% depending on which coefficient was used. West-Central Asian and Japanese groups detected in this study on the basis of PCRRFLP result can be considered separate species after interpretation of inter-strain crosses, which have shown the existence of reproductive isolation barriers between West-Central Asian and Japanese strains on the basis of the percentage of surviving clones.