Isolates from ancient permafrost help to elucidate species boundaries in Acanthamoeba castellanii complex (Amoebozoa: Discosea)

Acanthamoeba castellanii species complex (genotype T4) comprises of more than ten species with unclear synonymy. Its molecular phylogeny has several conflicts with published morphological data. In this paper, we analyze morphometric traits and temperature preferences in six new strains belonging to A. castellanii complex isolated from Arctic permafrost in the framework of molecular phylogeny. This integrative approach allows us to cross-link genotypic and phenotypic variability and identify species-level boundaries inside the complex. We also analyze previously known and newly found discrepancies between the nuclear and mitochondrial gene-based phylogenies. We hypothesize that one reason for these discrepancies may be the intragenomic polymorphism of ribosomal RNA genes.