Slipper animacule

Image taken from micro*scope

Paramecia were among the first ciliates to be seen through early microscopes in the late 17th century. The first description occurs in a letter by his contemporary Christiaan Huygens in 1678. Huygens was a prominent Dutch mathematician and scientist. Interestingly is not known for this particular discovery but more for his telescopic studies of the rings of Saturn and the discovery of its moon Titan which was honored by   the European Space Agency (ESA) by naming an atmospheric entry probe after him. The probe landed successfully on Titan in 2005. Huygens was clearly one of those all-round talents that were typical for scientists at that time, e.g. he also invented the pendulum clock. 

But back to the paramecia - in 1718, the French mathematics teacher Louis Joblot published a description and illustration of what he called "slipper animacule". In some countries this phrase still remains the common name for members of the genus Paramecium. The widely used German term "Pantoffeltierchen" literally means slipper animal. The name relates to the typically ovoid, elongate, foot- or cigar-shaped cell usually ranging from 50 to 300 micrometres in length. 

Paramecia are widespread in freshwater, brackish and marine environments, and are often very abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, Paramecium has been widely used in classrooms and laboratories to study biological processes. I am fairly confident that many of my readers had an encounter with Paramecium at school or university. Consequently, some Paramecium species such as Paramecium aurelia or Paramecium caudatumare are among the best known protozoans. Other groups are almost unexplored and in most cases we know little about their DNA sequence variation which seems to be fundamental for the determination of boundaries between those species. Some studies have revealed the existence of reproductively isolated groups within Paramecium as well as other ciliates. Those were initially called syngens which stands for “generating together”. In some cases syngens were recognized as sibling cryptic species but in other cases the isolation between syngens is imperfect, thus not each syngen is equivalent to a true cryptic species. 

One of those less widely know species is Paramecium putrinum. It is one of the smallest members of the genus, a cosmopolitan, freshwater species, that prefers cold and moderate-climate regions. A neat little new study provides a closer look at this species and potential existence of cryptic variation within it:

Herein we present an assessment of molecular variation in 27 strains collected from widely separated populations by using two selected DNA fragments (ITS1-5.8S-ITS2-5′LSU rDNA and COI mtDNA). Both the trees and haplotype networks reconstructed for both genome fragments show that the studied strains of P. putrinum form five main haplogroups. The mean distance between the studied strains is p-distance = 0.007/0.068 (rDNA/COI) and exhibits similar variability as that between P. bursaria syngens. Based on these data, one could hypothesize that the clusters revealed in the present study may correspond to previously reported syngens and that there are at least five cryptic species within P. putrinum.