Three-locus analysis in conjunction with strain crosses confirms the existence of reproductively isolated populations in Paramecium jenningsi

Abstract

Paramecium jenningsi (Diller & Earl, 1958) was formerly considered to be a species with only one syngen (genetic species) based on an inter-strain cross of two strains, cytological analysis, and an investigation of esterases and acid phosphatases. However, the existence of syngens within the species was later suggested by genetic studies, i.e. classical strain crosses of new strains and molecular PCR-based analyses (RAPD, RFLP), as well as by sequencing the H4 gene fragment. This issue still needs to be clarified by the application of molecular markers, genetic tests and cytological preparations. In the present study, we tested 12 strains of P. jenningsi originating from Asia, North America and Africa. Trees reconstructed on the basis of three genome fragments (ITS1-5.8S-ITS2-5’LSU, COI and CytB) show that P. jenningsi is divided into two distinct clusters (PJ1, PJ3) and one branch (PJ2) which correspond to reproductively isolated groups revealed by strain crosses. A study based both on strain crosses and a three-locus comparison gives the opportunity for a more complete identification of the reproductively isolated populations of P. jenningsi and other ciliate species.

Key words:

• Ciliophora
• intraspecific polymorphism
• Paramecium jenningsi
• strain crosses
• syngens
• three-locus analysis

Acknowledgements

This study was supported by a grant from the National Centre of Science, Cracow, Poland, No. 2012/05/B/NZ8/00387, and was also carried out in the context of the CNRS-supported European Research Group ‘Paramecium Genome Dynamics and Evolution’ (GDRE) and the European Cooperation in Science and Technology (COST BM 1102). We thank Dr Alexey Potekhin (Department of Microbiology, Faculty of Biology and Soil Science, St. Petersburg State University, Russia) for strain P. putrinum from the Core Facilities Centre “Culture Collection of Microorganisms” of St. Petersburg State University used in the studies. Finally, we would like to thank the Associate Editor and two anonymous reviewers for their constructive comments.

Associate Editor: Elliot Shubert