Sequence analysis of the cytb gene of Mesocestoides Vaillant, 1863 tetrathyridia from small mammals of the Russian Far East

This paper continues a series of articles concerning the molecular genetic analysis of widespread helminths – cestodes of the genus Mesocestoides Vaillant, 1863, parasitising (at the metacestode stage) small mammals. In this study, we examine the genetic diversity of Mesocestoides spp. from micromammals of the Russian Far East using the cytb gene as an example. Polymorphism of the nucleotide sequence of the cytochrome b gene and the amino acid sequence of the encoded polypeptide was detected for the first time in Mesocestoides spp. parasitising hosts of different genera and species inhabiting this region. Two species of Mesocestoides spp. were identified that were not related to the genetically confirmed species of the genus. One of them was found only in Micromys minutus (Pallas, 1771), obtained near Georgievka village in Khabarovsk Territory. The second species is represented by nine individuals from geographically distant locations, in which two genetic sublines and 11 nucleotide differences in the cytb gene sequence were found. Molecular diversity indices show a high level of polymorphism in the nucleotide sequence of this gene in the gene pool of the studied species of Mesocestoides. In addition, the presence of three isoforms of the cytochrome b polypeptide was established. Analysis of amino acid substitutions in these polypeptide isoforms and the polypeptide from the M. minutus sample also indicates that the latter belongs to a separate species.