My research work takes advantage of the large body of molecular and ecological information available for the ciliate Paramecium, to address a number of evolutionary as well as population genetics issues (see below).

What is Paramecium?

Paramecium is a genus of protozoa (unicellular eukaryotes), that includes species which are one or a few hundreds micrometers in size and widespread in freshwater environments. Among these species, P. aurelia is the most studied since the first decades of 1900. While Christian G. Ehrenberg originally identified P. aurelia as a single species (1838), the developer of the genetics of Paramecium - T. Sonneborn - later (1975) showed that P. aurelia is in fact a species complex. Today the P. aurelia complex includes 15 species.

A large number of biological processes have been closely examined in Paramecium, some being the role played by the cytoplasm in symbiont and cortical inheritance (see for example the work of J.R. Preer and J. Beisson) and the homology-dependent maternal inheritance (see for example the work of J. Forney and E. Meyer). The macronuclear genome of one of these sibling species, namely P. tetraurelia, has been sequenced and is now available.

Research Projects

• The genetic effective population size (Ne) of a species mediates the relative effects of selection. Observations suggest that Ne is negatively correlated with organism size over a wide phylogenetic range of species (Lynch and Conery 2003; Lynch 2006). For unicellular organisms, however, most Ne estimates are derived either from taxa with poorly understood species boundaries or from host-restricted pathogens, which complicate the estimate of Ne. Moreover, that Ne is elevated in free-living single-celled organisms still remains a controversial issue.

  Aiming to solve this controversy, we will estimate the amount of variability at silent sites for a relatively large number of genes in each or most of the species belonging to the Paramecium aurelia complex. This analysis will also be instrumental to characterize intron variability and turnover rate across P. aurelia species.

• Paramecium has two nuclei. The DNA that resides in the macronucleus (somatic) is a rearranged version of the DNA located in the micronucleus (germline). Upon the formation of the macronuclear genome, micronuclear-specific DNA sequences called IESs (Internal Eliminated Sequences) are precisely excised. Only ~ 80 IESs have been detected in Paramecium so far, while more than 50,000 IESs are estimated to be present in Paramecium tetraurelia micronuclear genome. The detected IESs tend to be generally short (26 to 883 bp) and AT reach, do not contain ORFs or strictly conserved flanking motifs. IESs identification is mainly aggravated by the virtual lack of micronucleuar genome sequence information.

  Our goals are i) to increase the number of known germline specific genomic regions in P. tetraurelia as well as in other aurelia species, ii) to characterize the intra and interspecific variability of these germline specific sequences and iii) to analyse the IESs turnover rate across P. aurelia species.