The Multiple Mating Type System of the Marine Ciliate Euplotes crassus (Dujardin)

Sex in the wild: repeated observations of planktonic ciliate conjugation from field samples

Ciliate conjugation is considered a rare event to encounter in the field and it is mostly reported from cultures. In this work, we describe a synchronized conjugation event of planktonic ciliates that was discovered twice; in September 2019, at two different locations in the Cretan Sea, Eastern Mediterranean, and in October 2020. In 2019, first, at 2 m depth of the coastal station POSEIDON-HCB, in samples fixed with acid Lugol and formaldehyde, we found 340 and 200 mating pairs L^-1of different ciliate species, respectively; and second, at the Heraklion port, we found 220 mating pairs L^-1 of Strombidinopsis sp. and 1960 mating pairs L^-1 of Strombidium sp. At the Heraklion port visited again in 2020, we found 800 mating pairs L^-1 of Strombidinopsis sp. and 200 mating pairs L^-1 of Strombidium sp. Since detailed descriptions of conjugation in pelagic oligotrich ciliates are missing, our observations indicate that ciliate conjugation could be a frequent and periodic phenomenon, under specific conditions.

Characterization of Euplotes lynni nov. spec., E. indica nov. spec. and description of E. aediculatus and E. woodruffi (Ciliophora, Euplotidae) using an integrative approach

Four species belonging to the genus Euplotes have been investigated, namely: E. lynni nov. spec., E. indica nov. spec., E. aediculatus, and E. woodruffi. All populations are from India and were investigated using morphological and molecular markers. The phylogenetic relationships were inferred from small subunit ribosomal rRNA gene (SSU rRNA), internal transcribed spacer (ITS) region, and mitochondrial cytochrome c oxidase subunit I (COI) gene. Predicted secondary structure models for two new species using the hypervariable region of the SSU rRNA gene and ITS2 region support the distinctness of both species. Morphological characters were subjected to principal component analysis (PCA) and genetic variations were studied in-depth to analyze the relatedness of the two new species with their congeners. An integrative approach combining morphological features, molecular analysis, and ecological characteristics was carried out to understand the phylogenetic position of the reported species within the different clades of the genus Euplotes.

Genic determination of the autogamy trait in the hypotrich ciliate,Euplotes crassus

Cross-fertilizing stocks ofEuplotes crassus, differing as to the ability to undergo autogamy, were subjected to breeding analysis. The resulting data are consistent with the interpretation that a single locus (a) with a pair of alleles (a+;a−) controls the ability to undergo autogamy. The two alleles express a simple dominance relationship in which the dominant allele (a+) permits expression of the autogamy trait. Cross-breeding experiments also suggest that thealocus is not linked to themtlocus which determines the mating-type trait.

Purification and characterization of new mating pheromones of the ciliate Euplotes raikovi

Cell union in mating pairs in the ciliate Euplotes raikovi is controlled by a system of multiple mating types which are inherited with alleles codominant at the genetic locus mat and expressed via diffusible mating pheromones. The mating pheromones Er-2, Er-3, and Er-11 were purified from cells homozygous for the mat-2, mat-3, and mat-11 alleles, respectively. These pheromones are proteins of similar Mr (11,000-12,000) and acidity (pI 3.7-4.0) and are active at a concentration that varies from 2.9 X 10(-12) to 1.2 X 10(-11) M. Data on amino acid composition revealed that an unusually high amount of cysteine (12-15.7%) and poor contents of basic amino acids are common to every pheromone. On the basis of this uniformity in the main biochemical traits, which also holds for the previously purified pheromone Er-1, it was concluded that E. raikovi mating pheromones are members of a family of proteins structurally diversified from each other to varying extents.