Barcoding Heliozoa: Perspectives of 18S rDNA for Distinguishing Between Acanthocystis Species

The first application of DNA-barcoding for the centrohelids is reported. The character-rich genus Acanthocystis was chosen to compare sequence divergence and morphological similarity. Acanthocystis nichollsi, an easily identifiable and well outlined species, was isolated from four remote locations; A. costata; A. takahashii (2 strains) and A. turfacea were studied as well. Detailed light- and electron-microscopic data were obtained and a fragment of 18S rDNA (mostly V5 to V8 regions) was cloned and multiple clones were sequenced. Obtained data allowed a comparison of the level of genetic divergence between several strains of one and the same morphospecies from remote locations and several strains of different morphospecies. This analysis showed no overlap between intraspecific and interspecific divergence. Phylogenetic analysis also recovered the clades for all species correctly. The genetic divergence between individual molecular clones obtained from the same clonal culture allowed accessing the genetic structure of the local populations of heliozoans. The level of divergence inside of the morphological species suggests a possible cryptic speciation. In some subclades of A. nichollsi the sequence polymorphism caused mingling of strains on the tree. 18S rDNA was shown to be an appropriate barcode at the specific level, but the intra-strain polymorphism needs further attention.