Worldwide sampling reveals low genetic variability in populations of the freshwater ciliate Paramecium biaurelia (P. aurelia species complex, Ciliophora, Protozoa)

Abstract

Species (or cryptic species) identification in microbial eukaryotes often requires a combined morphological and molecular approach, and if possible, mating reaction tests that confirm, for example, that distant populations are in fact one species. We used P. biaurelia (one of the 15 cryptic species of the P. aurelia complex) collected worldwide from 92 sampling points over 62 years and analyzed with the three above mentioned approaches as a model for testing protistan biogeography hypotheses. Our results indicated that despite the large distance between them, most of the studied populations of P. biaurelia do not differ from each other (rDNA fragment), or differ only slightly (COI mtDNA fragment). These results could suggest that in the past, the predecessors of the present P. biaurelia population experienced a bottleneck event, and that its current distribution is the result of recent dispersal by natural or anthropogenic factors. Another possible explanation for the low level of genetic diversity despite the huge distances between the collecting sites could be a slow rate of mutation of the studied DNA fragments, as has been found in some other species of the P. aurelia complex. COI haplotypes determined from samples obtained during field research conducted in 2015-2016 in 28 locations/374 sampling points in southern Poland were shared with other, often distant P. biaurelia populations. In the Kraków area, we found 5 of the 11 currently known COI P. biaurelia haplotypes. In 5 of 7 reservoirs from which P. biaurelia was obtained, two different COI haplotypes were identified.

Paramecium bursaria—A Complex of Five Cryptic Species: Mitochondrial DNA COI Haplotype Variation and Biogeographic Distribution

“…The remaining haplotypes mainly have a narrow distribution restricted to one locality. The existence of similar haplotype network patterns (one to four dominant haplotypes and most haplotypes from a single locality) have been observed in P. biaurelia [86] or in P. trijenningsi [38]. This may indicate the absence of geographic barriers and the relatively rapid spread of closely related P. bursaria populations, with temperature being a key factor.…”

Cryptic Diversity in Paramecium multimicronucleatum Revealed with a Polyphasic Approach

“…Instead, all sibling species of the P. aurelia complex are either very rare or, if widespread, are represented all over the world, though with certain climatic preferences. For example, P. biaurelia occurs frequently only in moderate climate zones [ 63 , 64 ], while P. sexaurelia tends to occur in low latitudes [ 65 ]. Thus, the known principle “everything is everywhere” cannot be directly applied to Paramecium , though the geographic zones inhabited by many Paramecium species continue to expand with extensive sampling in previously unexplored regions [ 19 , 54 , 66 ].…”

Paramecium Diversity and a New Member of the Paramecium aurelia Species Complex Described from Mexico

“…is a separate species and not just a divergent group in P. biaurelia. Interestingly, P. biaurelia, the most common species of the P. aurelia complex in cold and moderate climate zones, at least in Europe [57], is not known from tropical environments [4,58], which may shelter its twin species, P. quindecaurelia n. sp. Sequence availability.…”